Nature’s Chemistry

Organic Chemistry

In this unit traditional organic chemistry is studied in the context of a wide range of everyday consumer goods. The chemistry of the important functional groups within these substances is emphasised, as are the characteristic chemical reactions.

Nature’s Chemistry

Organic ChemistryFrom previous work you should know and understand the following:

•That molecular structure and physical properties of hydrocarbons are related.•The names, molecular and structural formula of alkanes (C1-C8), alkenes (C2-C8) and cycloalkanes (C3-C8) straight and branched.•How to identify isomers and draw their structural formulae.•What is meant by saturated and unsaturated carbon compounds and how they can be distinguished.•Addition reactions

Nature’s Chemistry

Organic ChemistryFrom previous work you should know and understand the following:

•Alcohols functional group –OH and properties of alcohols•The names, molecular and structural formula of alcohols (C1-C8), straight and branched.•Carboxylic acids functional group COOH and properties of carboxylic acids•The names, molecular and structural formula of carboxylic acids (C1-C8), straight and branched.

Originally, chemical compounds were divided into 2 classes:Inorganic or Organic

Organic compounds were derived from living things. It was believed that they contained a ‘vital force’ and couldnot be made from inorganic compounds (non-living sources).

Organic chemistry is the study of carbon compounds

Organic Chemistry

Organic ChemistryOrganic chemistry is basically the study of compounds containing carbon (with the exclusion of oxides and carbonates).

There are so many compounds containing carbon that a whole branch of chemistry is devoted to their study.Organic molecules may be as simple as methane, CH4

or as complicated as cholesterol

HO

Fruity Flavours

Overview

In this section, learn about the characteristic chemistry and uses of esters, and find out how they are made by condensation reactions and broken down by hydrolysis.

a) Esters

Learning intention

Learn how esters are named and identified and how to draw the structural formula of an ester.

Esters

Alcohol + Carboxylic Acid Ester + Water

Esterification, Alkanoic acids reacting with Alkanols.

H+

Esters have sweet smells and are more volatile than carboxylic acids.They are responsible for sweet fruit smells. 280 aromas make up a strawberry smell!!

•3-methylbutyl ethanoate in bananas. •2-aminobenzoate is found in grapes. We imitate these smells by manufacturing flavourings. •Esters are also used in perfumes. •Esters can also be used as solvents in glues.•Polyesters are used to make plasticisers.•Methyl ester is a biodiesel.

Naming Esters

Second, find the C=O in the carboxylate group, this gives the 2nd word with the ending –oate. This comes from the acid.

First, the 1st word comes from the alcohol. The name ends in –yl.

ethyl propanoate

CH3 CH2 COO CH2 CH3

C2H5 C

O

O C2H5

R-OH + R’-COOH R’-COOR + Water

R-yl

R’-oate

FirstSecond

Naming carboxylic acids and estersAdvice from the BBC on naming organic compounds.

b) Making Esters

Learning intention

Learn about how esters are formed by condensation reactions of carboxylic acids and alcohols.

Making Esters

One way of preparing esters is to condense an alcohol with a carboxylic acid:

R O H H OC R'

O

+ R OC R'

O+ H2O

alcohol carboxylic acid ester

The reaction is slow at room temperature and the yield of ester is low. The rate can be increased by heating the reaction mixture and by using concentrated sulphuric acid as a catalyst. The presence of the concentrated sulphuric acid also increases the yield of ester.

The aim of this experiment is to prepare an ester and to identify some of the characteristic properties of esters.

Ester formation

+

Condensation Reaction

The reaction is brought about by heating a mixture of a carboxylic acid and an alcohol with a little concentrated sulphuric acid. (which acts as aCatalyst and absorbs the water produced).

methyl ethanoate

CH3COOCH3 + H20

R C

O

O R

Ester link

R

O

O R

C

R C

O

HO

R

H

OH

O

H+

CH3OHCH3COOH +

ethanoic acid methanol

Animation esterification

Making estersProcedureDecide which alcohol and carboxylic acid you need to make each ester in the table.

1. Before collecting the alcohol and carboxylic acid set up a water bath using the larger beaker and heat the water until it boils. Turn off the Bunsen.

2. Add the alcohol to a test tube to a depth of about 1 cm. To this add about the same volume of carboxylic acid. If the acid is a solid then use a spatulaful.

3.In the interests of safety your teacher/lecturer may carry out the next step.

Add about 5 drops of concentrated sulphuric acid to the reaction mixture.

Making esters

4. Soak the paper towel in cold water, fold it up and wrap it round the neck of the test tube. Secure it with a rubber band. This arrangement acts as a condenser when the reaction mixture is being heated.

5. Place a loose plug of cotton wool in the mouth of the test tube. This will contain any chemicals which may spurt out of the reaction mixture when it is heated.

6.Place the test tube in the hot water bath

Making esters

7. While the reaction mixture is being heated add about 20 cm3 of sodium hydrogencarbonate solution to the small beaker.

8. After about 10 minutes, take the test tube from the water bath and remove the plug of cotton wool. Slowly pour the reaction mixture into the sodium hydrogencarbonate solution. This neutralises the sulphuric acid and any remaining carboxylic acid and so removes the smell of the carboxylic acid.

9. Gently swirl the contents of the beaker and look to see if there is any sign of the ester separating from the aqueous mixture.

10. To smell the ester with your nose at least 30 cm from the mouth of the beaker gently waft the vapour towards your nose and take just a sniff.

c) Uses of Esters

Learning intention

Learn about the many everyday uses of esters.

Uses of esters

Esters are also used as non-polar industrial solvents.

Name Shortened Structural Formula Odour/FlavourCH3(CH2)4CH3 BananaCH3(CH)7CH3

Methyl Butanoate Pineapple3-Methylbutyl Butanoate CH3(CH2)2(CH2)2CH(CH3)2 Apple

CH3COOC3H7 PearMethyl-1-butyl ethanoate CH3COOCH(CH3)C4H9 Banana2-Methylpropyl methanoate Raspberry

C3H7COOC5H11 Apricot, StrawberryBenzyl ethanoate CH3COOCH2C6H5 Peach, flowersEthyl methanoateMethyl 2-aminobenzoate C6H4(NH2)COOCH3 GrapesBenzyl butanoate C3H7COOCH2C6H5 Cherry

Esters are oily liquids with generally very pleasant fruity smells and have a range of uses.Many esters are used as flavourings and in perfumes. Natural fruit flavours contain subtle blends of some of the esters in the table below:

Uses of esters

Factors affecting perfume design e.g. using esters:

Designing a perfume - several issues to address by way of design factors.

The perfume needs to be a mixture of compounds to give a prolonged perfumery effect.

The perfumer chemist has to design the mixture to give a particular fragrance which includes ...

 the top note - the first fragrant molecule to be released, and the low note, the last molecule to be vapourised.

Uses of esters

Esters are also used as non-polar industrial solvents.

Some of the smaller esters are quite volatile and are used as solvents in adhesives, inks and paints – pentyl ethanoate is used in nail varnish for example.

Uses of estersEthyl ethanoate is one of a number of solvents used to extract caffeine from coffee and tea.

De-caffeinated products produced with ethyl ethanoate are often described on the packaging as "naturally decaffeinated" because ethyl ethanoate is a chemical found naturally in many fruits.

Uses of esters

Caffeine (C8H10N4O2) is an example of a class of compounds called alkaloids which are produced by plants.

The name alkaloid means “alkali-like”, where alkali is a base and hence refers tothese basic properties.

Carryout the experiment to extract caffeine from tea.

Uses of esters

.

Caffeine is more soluble in the organic solvent ethyl ethanoate than in water, so we will extract caffeine into the organic solvent to separate it from glucose, tannins, and other water soluble compounds using a separating funnel.

The ethyl ethanoate portions can be combined and the ethyl ethanoate removed by evaporation to leave the caffeine

c) Hydrolysis of Esters

Learning intention

Learn how esters can be broken down by hydrolysis into the parent carboxylic acid and alcohol.

Hydrolysing Esters

Alcohol + Carboxylic Acid Ester + Water

Alcohol + Carboxylic Acid Ester + Water

Condensation

Hydrolysis

The ester is split up by the chemical action of water, hydrolysis.The hydrolysis and formation of an ester is a reversible reaction.

R C

O

O R H

O

H+

Bonds broken

Ester + Water

+R C

O

HO

R

H

O

Bonds formed

Carboxylic Acid + Alcohol

http://www.educationscotland.gov.uk/highersciences/chemistry/consumerchemistry/fruitflavours/makingesters.asp

Percentage yieldsCH3COOH + CH3CH2CH2OH <=> CH3COOCH2CH2CH3 + H2O

4.3 g of propyl ethanoate was produced when 6 g of ethanoic acid was reacted with propan-1-ol. What is the percentage yield of the ester?

Percentage yield = actual yield/theoretical yield x 100%

Fats and oils

Overview

In this section, study the chemistry and structure of edible fats and oils, and learn how the difference in melting points of fats and oils can be explained in terms of structural differences.

a) Edible fats and oils

Learning intention

Learn about the characteristic properties of fats and oils and study how they are formed by a condensation reaction of glycerol with fatty acids.

Fats in the DietFats provide more energy per gram than carbohydrates.

Fat molecules are insoluble, and tend to group together and forma large droplet. This is how fat is stored in the adipose tissue.We store our extra energy as fat.

The type of fat we eat is important. Animal fats contain important fatsoluble vitamins. Oils, are thought to be healthier than solid fats, asthey are less likely to be deposited inside our arteries.

However, there is an ongoing debate about which fats are better for us.Polyunsaturated fats are considered to be less potentially harmful to theheart.

Fats and oils

Naturally occuring

Animal fat

Vegetable oil

Marine oil

lardsuet

sunflower oilcoconut oil

cod liver oilwhale oil

Fats and OilsFats and oils are a range of substances all based on glycerol,propane-1,2,3-triol.

Natural fats and oils are a mixture of triglyceride compounds.

50% of yourbrain is fat.

Each OH group can combine chemically with one carboxylic acidMolecule. The resulting molecules are fats and oils.They are described as triglycerides.

The hydrocarbon chain in each can be from 4 to 24 C’s long.The C’s can be single bonded (saturated) or double bonded (unsaturated).

C

C

C

O

O

O

H

H H

H H

H

H

H

Glycerolpropane-1,2,3-triol

a trihydric acid

Fats and oils

glycerol

Systematic name is propane-1,2,3-triol

Fats and oils are built from an alcohol with three -O-H groups.

Fatty AcidsCH3(CH2)16COOH

CH3(CH2)7CH=CH(CH2)7COOH

Stearic Acid (suet, animal fat) Saturated

Oleic Acid (olive oil) Unsaturated

Octadec-9-enoic acid

Oleic acid 47%

Palmitic acid

24%

Linoleic acid 10%

Stearic acid 8%

Humans fatty acids

C17H35COOH

C17H33COOH

CH2

CH2

CH2

CH2

CHCH

CH2

CH2

CH2

CH2

CH2

CH2

CH2C

O

OHCH

2

CH2

CH2

CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

CH3

Fats and oils

Stearic acid

Systematic name is octadecanoic acid

The other components of fat molecules are carboxylic acidssuch as

Fats and oils

Fats and oils are ESTERS of glycerol andlong chain carboxylic acids

Fats and oilsRemoval of water in the condensation reaction gives -

The molecular formula shown above suggests that the fat molecule is shaped like an E, but the molecule is actuallyshaped more like this:

b) The melting point of fats and oilsLearning intention

Learn how differences in structure of fats and oils lead to differences in strength of intermolecular forces, and therefore to differences in melting points.

.

Fats and oils

Fats are mainly built from carboxylic acids with C-C single bonds.

Oils have some C=C bonds in the carboxylic acids from which they are made.

Stearic acid in beef fat

Oleic acid in olive oil

Oil

Fat

Fat molecules pack together more tightly,making fats solid at room temperature.

Double bonds in oil make the molecule less compact.Less tightly packed molecules make oils liquid.

Fats and oils

Oil

Fat

Double bonds in oil make the molecule less compact.

Fat molecules pack together tightly, making fats solid at room temperature.

Less tightly packed molecules make oils liquid because the bonds between molecules are weaker.

Hydrogenation

The addition of hydrogen to an unsaturated oil will ‘harden’ the oil. Increase it’s m.p.The hydrogen is added across the double bond.Used with margarine, otherwise margarine would be a liquid when taken out of the fridge.

http://www.educationscotland.gov.uk/highersciences/chemistry/animations/oilsfats.asp

Unsaturation in fats and oils1. Using a plastic pipette, add five drops of olive oil to 5

cm3 of hexane in a conical flask.

2. Use a burette filled with a dilute solution of bromine water (0.02 mol dm–3) (Harmful and irritant). Read the burette.

3. Run the bromine water slowly into the oil solution. Shake vigorously after each addition. The yellow colour of bromine disappears as bromine reacts with the oil. Continue adding bromine water to produce a permanent yellow colour.

4. Read the burette. Subtract to find the volume of bromine water needed in the titration.

5. Repeat the experiment with: five drops of cooking oil (vegetable) and five drops of cooking oil (animal).

Unsaturation in fats and oils

Fats and OilsThe degree of saturation in a fat or oil can be determined by theIodine Number. (bromine can also be used).The iodine reacts with the C=C bonds, so the greater the iodine number, the greater the number of double bonds.

Omega 3 fatty acids make up a large % of your brain’s fat.

Solid fats – butter, beef fat & lard have low iodine numbers because they are more saturated than the unsaturated oils.

Fat Av Iodine No

Butter 40

Beef Fat 45

Lard 50

Olive Oil 80

Peanut Oil 100

Soya Bean Oil

180

Margarine is made from vegetable oils, butterfrom animal fats. One reason why margarine spreads better!

In practice both fats and oils are mixtures of esters containing both saturated and unsaturated compounds.Beef Fat

Olive oil

In general oils have a higher proportion of unsaturated molecules.

Structures of Fats and OilsHydrolysis of a fat or oil produces a molecule of glycerol (alcohol) for every 3 carboxylic acid molecules. The carboxylic acids are usually called long chain fatty acids. Most fats and oils are, in fact, esters of propane-1,2,3-triol, sometimes called, triesters.

R 1,R 2,R 3 are long carbon chains,

which can be the same or different

Glycerol part

Fatty acid part

C

C

C

O

O

O

H

H C

H C

C

H

H

O

R1

O

R2

O

R3

Hydrolysis

Glycerol + Fatty Acids

Triesters.

Proteins

Overview

In this section, study the structure and function of proteins. Learn about how they are formed from amino acids in condensation reactions, and how they are broken down by hydrolysis.

a) Function of proteins

Learning intention

Learn about the function of proteins in living things.

Proteins

• Introduction to proteins

An animation of three proteins which demonstrate common structural elements despite their very different functions.

Globular proteinsProteins which operate within cells need to be soluble. The polypeptide chainsare coiled together in spherical shapes. E.g. Haemoglobin and many hormones.e.g. Insulin, was the first protein structure to be worked out. Enzymes are globular proteins.

Protein StructuresSome proteins are composed of a single polypeptide chain, but many consistof two or more polypeptide chains.

Proteins are classified according to their shape into fibrous and globularproteins.

Fibrous proteinsThese have their polypeptide chains interwoven. The polypeptide chains areheld together by hydrogen bonding, between the N-H and the C=O groups.

This gives these proteins their properties of toughness, insolubility, and resistance to change in pH and temperature. So they are found in skin,tissue,(collagens), hair, nails (keratins).

Silk is a typical example of a fibrous protein.

This view shows the protein chains contain 2 different amino acids.

This view shows the individual atoms in the protein chains.

Silk

Protein Structures

Albumen, in egg white, is a globular protein..

backbone view atom view

Albumen

Protein Structures

Enzymes are globular proteins. The structure of amylase is shown below.

Protein Structures

Starch molecule in the enzyme’s active site.

Enzyme ActivityEnzymes catalyse chemical reactions in the body. Each enzyme has a unique shape held together by many weak bonds. Changes to pH and temperature can denature the enzyme. This changes the enzymes shape stops it working properly.

The bonds that hold most biological enzymes are broken around 60oC.

Temp or pH

Enzymeactivity

Narrow optimum range

Enzyme Activity, Lock and Key

The critical part of an enzyme molecule is called its active site.This is where binding of the substrate to enzyme occurs and where catalysis takes place. Most enzymes have one active site per molecule.

Substrate

Enzyme

Enzyme Activity, Lock and Key

Substrate

Enzyme

Active site

Enzyme Activity, Lock and Key

The substrate becomes activated

Enzyme

Enzyme Activity, Lock and Key

The substrate becomes activated

Enzyme

Enzyme Activity, Lock and Key

The complex molecule splits

Enzyme

Enzyme Activity, Lock and Key

The complex molecule splits

Enzyme

b) Amino Acids

Learning intention

Learn about the characteristic chemistry of amino acids, the building blocks of proteins.

Amino acidsAll proteins contain the elements C,O,H, N. They are condensation polymers, made by amino acids linking together.

The body cannot make every type of amino acids that it needs. So our diet must contain essential amino acids. (about 10 of them). We synthesis the others.

When R is Hydrogen, the amino acid is glycine (Gly) (aminoethanoic acid)

When R is CH3, the amino acid is alanine (Ala) (2-aminopropanoic acid)

Amino Acids

NH2CHCOOH

R Most proteins contain 20+ different amino acidsH N

H

C C O H

R O

H

Amino acids

This animation illustrates the process of protein formation by the condensation of the carboxylic acid and amine groups of amino acids. It also looks at the reverse process of protein hydrolysis

http://www.educationscotland.gov.uk/highersciences/chemistry/animations/chemicalequations.asp

c) Amide links

Learning intention

Learn how proteins are formed by condensation reactions of amino acids to produce amide (peptide) links.

Protein Polymers

Proteins are condensation polymers, made by amino acids linking together. An amine group of one molecule links to the carboxyl group of another molecule to form an amide link or peptide bond.

Protein Polymers

Tripeptide, ala-gly-ala

Polypeptide chain can have 10000 amino acids

N – C - C

CH3 H CH3

+ +

alanine glycine alanine

H

H

O

OHH

N – C - CH

H

O

OHH

N – C - CH

H

O

OHH

O

N – C – C -

CH3

N – C – C -

H

N – C - C

CH3OH H

H

H

H+ 2H2O

O

OH

H

H

amide (peptide) link

d) Hydrolysis of protein

Learning intention

Learn how proteins are broken down to amino acids by the process of hydrolysis.

Protein hydrolysisProteins are broken down during digestion. Digestion involves the hydrolysis of proteins to form amino acids

Protein

Aminoacids

+ 2H2O

Identifying amino acids by chromatography

In the lab a protein can be hydrolysed back to its constituent amino acids by refluxing with concentrated hydrochloric acid for several hours.

Amino acids can be identified by the use of paper (or thin layer) chromatography.

A piece of chromatography paper is spotted with some amino acids suspected as being present and also with the hydrolysed protein.

Identifying amino acids by chromatography

By comparing the position of the spots of the known amino acids with that of the hydrolysed protein, the amino acids in the protein can be identified.•Add your results to the diagram•The hydrolysed fruit juice contained?

Chemistry of cooking

Overview

In this section, learn how functional groups in volatile molecules influence food flavour, and find out how cooking affects the structure of protein in food.

a) Flavour in food

Learning intention

Learn how the chemistry of certain functional groups in volatile molecules in foods influence flavour.

The chemistry of flavour

The chemistry of flavourMolecules responsible for flavour in vegetables are normally trapped inside the cell walls. During cooking the cell walls are damaged for two reasons:

• Chemical damage occurs as the cell walls, which are made of cellulose, break down.• Physical damage occurs as water inside the cells boils forming steam and the cell walls break open.

The chemistry of flavour

A major issue in cooking is to retain molecules responsible for flavour in the food – overcooking can result in loss of these molecules. One destination for lost flavour molecules is in the cooking water. This will occur if the flavour molecules are water-soluble. If this is the case, many of the flavour molecules will be lost down the drain when the cooking water is poured away.

The chemistry of flavour

• What is flavour? Illustrates the idea that flavour is taste plus aroma, and shows tasting experiments in which a blindfolded taster holds his nose and becomes unable to identify flavour.

• Chocolat coulant Heston Blumenthal describes how to make a pudding containing chocolate and cheese and explains why this unlikely-sounding combination tastes good.

• Fire and spice: the molecular basis for flavor Explains the stereochemical theory of odour which suggests that a molecule that fits into an olfactory receptor can fire nerve cells, ultimately producing a particular odour perception

b) Flavour in food

Learning intention

Learn how heating protein-containing foodstuffs leads to a change in food texture as intermolecular forces are broken.

Changes in protein structure on heating

• Within proteins, the long chain molecules may be twisted to form spirals, folded into sheets, or wound around to form other complex shapes. The chains are held in these forms by intermolecular bonding between the side chains of the constituent amino acids. When proteins are heated, during cooking, these intermolecular bonds are broken allowing the proteins to change shape (denature).These changes alter the texture of foods.

• Cooking meat Experiments in which different cuts of meat are cooked under different conditions to determine the optimum cooking temperature.

Oxidation of foods

Overview

In this section, learn how oxidation reactions in foods convert alcohols to aldehydes and ketones, and study the role of antioxidants in the preservation of foods.

.

a) Oxidation of alcoholsLearning intention

In this section, learn about the products of oxidation of primary, secondary and tertiary alcohols. Find out about important mild oxidising agents and learn how to spot an oxidation reaction in a carbon compound.

Classification of alcohols

Primary alcohol, ONE C joined to theC bonded to the OH group

Secondary alcohol, TWO C’s joined to theC bonded to the OH group

Tertiary alcohol, THREE C’s joined to the C bonded to the OH group

2-methylpropan-2-olpropan-2-ol

CC H

H

H

H OH

H

C O

CH3

H

CH3

CH O

CH3

H

CH3

H3C

CH3C

CH3

H3C

OH

CC C

H

H

H OH

H

H H

H

Oxidation of Alcohols

Primary alcohols can be oxidised by a number of oxidising agents, in two stages, 1st Stage - Hydrogen is lost; 2nd Stage - oxygen is gained.

Secondary alcohols can be oxidised to form ketones, Tertiary alcohols do not undergo oxidation.

C

O H

H

H

+ OR C H

O

R

oxidation

H2O+

aldehyde

OO+C H

O

R

aldehyde

C H

O

R

Carboxylic acid

oxidation

R C R1

O

ketone

1st

2nd

When applied to carbon compounds, oxidation results in an increase in the oxygen to hydrogen ratio.

b) Aldehydes and ketones

Learning intention

Learn about the characteristic functional groups and chemical reactions of aldehydes and ketones. Study how aldehydes and ketones are named and drawn.

Aldehydes and Ketones

Methanal, 40% in water is formalin, and is used to make polymers

Propanone, nail varnish remover and is used in the making of perspex

Ethanal, It’s trimer (CH3CHO)3 is used as a sleep inducing drug. It also causes a hangover

Butanone, is a solvent used to make VHS tapes.

H

HC = O

-+

CH3

HC = O

CH3CH2

CH3

C = O

Butan-2-one C4H8O

CH3

CH3

C = O

Aldehydes and Ketones(Using mild oxidising agents.)Distinguishing tests

Aldehydes are oxidised to carboxylic acidsKetones do not react with mild oxidising agents

1. Fehlings solution contains Cu2+ ions (blue) which form Cu+ ion (orange-red) in the presence of aldehydes.

2. Tollen’s reagent contains Ag+ ions, which form Ag in the presence of aldehydes (silver mirror test)

3. Acidified Potassium Dichromate orange Cr2O72-(aq) to green

Cr3(aq)

Oxidation

C

O

H C

O

CC

aldehyde ketone

C O

This structural difference accounts for the fact that aldehydes can undergo mild oxidation to form carboxylic acids but ketones resist oxidation. Oxidising agents can therefore be used to distinguish between aldehydes and ketones.

The aim of this experiment is to use the mild oxidising agents, acidified potassium dichromate solution, Benedict's solution and Tollens' reagent, to distinguish between two given carbonyl compounds one of which is an aldehyde and the other a ketone.

INTRODUCTION Both aldehydes and ketones contain the carbonyl group.

In aldehydes a hydrogen atom is bonded to the carbonyl group but in ketones the carbonyl group is always flanked by carbon atoms:

OxidationProcedure1. Before collecting the carbonyl compounds X and Y set up a water bath and heat the water until it boils. Turn off the Bunsen.

2. Add sulphuric acid to each of two test tubes to a depth of about 2 cm. Then add potassium dichromate solution to both to give a total depth of about 3 cm in each.

3. To one of these test tubes add about 5 drops of compound X and to the other add about 5 drops of compound Y.

4.Place both test tubes in the water bath and observe and record any changes.

5.Add Benedict's solution to each of two test tubes to a depth of about 3 cm. 6. Repeat steps 3 and 4.

7. Add Tollens' reagent to each of two very clean test tubes to a depth of about 3 cm.

8. Repeat steps 3 and 4 and immediately after, wash the contents of the test tubes down the drain with large amounts of water.

Introducing alcoholThis page explains what alcohols are, and what the difference is between primary, secondary and tertiary alcohols.

Naming alcohols, aldehydes and ketonesInformation from BBC Bitesize on the rules for naming organic compounds.

c) Antioxidants

Learning intention

Learn about the chemistry of the antioxidant molecules which prevent oxidation reactions in foods from taking place.

Oxidation of food

• Oxidation reactions can occur when food is exposed to oxygen in the air.

• Foods containing fats or oils are at the greatest risk of oxidation.

Foods rich in fats and oils

Oxidation of Fats

Fats and oils, or foods containing them, are the most likely to have problems with oxidation. Fats react with oxygen and even if a food has a very low fat content it may still need the addition of an antioxidant. They are commonly used in: •vegetable oil •snacks (extruded) •animal fat •meat, fish, poultry •margarine •dairy products •mayonnaise / salad dressing •baked products •potato products (instant mashed potato)

http://www.understandingfoodadditives.org

When fats react with oxygen they are broken down, causing:

– deterioration of flavour (rancidity)

– loss of colour

– loss of nutritional value

– a health risk from toxic oxidation products.

Effects of oxidation on food

As the fat decomposes and reacts with oxygen, chemicals called peroxides are produced. These change into the substances characteristic of the smell and soapy flavour of a rancid fat.

Antioxidants prevent the formation of peroxides and so slow the process of the food 'going off'. Some antioxidants react with oxygen itself and so prevent the formation of peroxides. Air-tight packaging, using inert gases like nitrogen, vacuum packing and refrigeration can all be used to delay the oxidation process. However, these can still be inefficient and adding antioxidants can be an effective way of extending the shelf life of a product.

http://www.understandingfoodadditives.org

Fat breaking down

Oxygen

FatFat

Fat molecules

Fat

CH2

CH2

CH2

CH2

CH2

COO

CH2

CH3

CHH

H

CH2

CH2

CH2

CH2

CH

COO

CHCH3

C

C

O

H

H

CH2

CH2

CH2

CH2

CH2

CO

CH2

CH3

R CH2CH2CH2CH CH CH3

Radicals attack near the double bond(NB ‘R’ represents the remainder of the fat molecule)

Antioxidants

• Antioxidants are chemicals that are added to food to prevent the food from ‘going off’.

• An antioxidant is a substance that slows down or prevents the oxidation of another chemical.

Oxidative damage

• Oxidation reactions can produce free radicals.

• A free radical is a highly reactive species containing an unpaired electron.

• Free radicals can damage food by removal of an electron.

• Antioxidant molecules ‘mop up’ free radicals to protect the foodstuff.

Damaging free radical

Electrontransferred

Antioxidant Antioxidant converted to a stable free radical

Neutralised free radical

Radical now in a stable pair

How does an antioxidant cancel out a free radical?

The antioxidant molecule donates an electron to the potentially damaging free radical.

A stable electron pair is formed, stabilising the free radical.

The antioxidant itself becomes oxidised (loses an electron).

Antioxidant E-number Typical foods

Ascorbic acid (vitamin C)

E300 Beers, cut fruits, jams, dried potato. Helps to prevent cut and pulped foods from going brown by preventing oxidation reactions that cause the discolouration. Can be added to foods, such as potato, to replace vitamin C lost in processing.

Tocopherols E306 Oils, meat pies. Obtained from soya beans and maize. Reduces oxidation of fatty acids and some vitamins.

Butylated hydroxyanisole (BHA)

E320 Oils, margarine, cheese, crisps. Helps to prevent the reactions that break down fats and cause the food to go rancid .

Citric acid E330

Jam, tinned fruit, biscuits, alcoholic drinks, cheese, dried soup. Naturally-occuring in citrus fruits like lemons. Helps to increase the anti-oxidant effects of other substances. Helps to reduce the reactions that can discolour fruits. May also be used to regulate pH in jams and jellies.

The table shows some typical antioxidants:

http://www.understandingfoodadditives.org

Antioxidants in action

Oxidation occurs when the apple is left exposed to air

The apple is protected when dipped in orange juice containing the antioxidant vitamin C

Antioxidants

Oxidation reactions happen when chemicals in the food are exposed to oxygen in the air. In natural conditions, animal and plant tissues contain their own antioxidants but in foods, these natural systems break down and oxidation is bound to follow. Oxidation of food is a destructive process, causing loss of nutritional value and changes in chemical composition. Oxidation of fats and oils leads to rancidity and, in fruits such as apples, it can result in the formation of compounds which discolour the fruit.

Antioxidants are added to food to slow the rate of oxidation and, if used properly, they can extend the shelf life of the food in which they have been used.

http://www.understandingfoodadditives.org

Vitamin C (ascorbic acid)

• The antioxidant vitamin C can act as a reducing agent (electron donor), preventing oxidation (electron loss) from the foodstuff.

C6H8O6   C6H6O6  +  2H+  +  2e-

Ascorbic acid

Dehydroascorbic acid

Antioxidants and health benefits

There may be health benefits from the use of antioxidants. Oxidation reactions in the body could be linked to the build-up of fatty deposits that cause blockages in arteries that can cause heart attacks. Antioxidants may be important in preventing this and there could also be a link with the prevention of certain cancers, arthritis and other conditions. The picture is not yet clear and a great deal of research needs to be undertaken.

http://www.understandingfoodadditives.org

Do antioxidants help us live longer?

Studies involving 230.000 men and women across the UK have shown that there is no convincing proof that antioxidants have any effect on how long people can live. However 40% of women and 30% of men are reportedly taking these supplements and spending over £333 million on them per year.

Impact of antioxidants on health

The imbalance between free radicals and antioxidants can lead to disease and ill health. The 4 main non-enzymatic antioxidants melatonin, α-tocopherol (Vitamin E), ascorbic acid (Vitamin C) and β-carotene (precursor for Vitamin A) can be found in a range of foods in our diet. However medical opinions are divided as regards the impact these antioxidants have our on general health.

Free radicals in living cellsFree radicals are present in all living cell and are a part of the cell processes. However excessive free radicals in our cells can attack the cell membranes (the outer coat of the cell). This attack causes cell and tissue damage.Radicals can also break strands of DNA (the genetic material in the cell). Some of the chemicals known to cause cancer, do so by forming free radicals.

MelatoninThis is a hormone which helps to regulate sleep in our bodies. This compound can be termed as a terminal or suicidal antioxidant as once it has removed the free radicals it has to be replaced.

OCH3

NH NH CH3

O

α-tocopherolThis is a form of vitamin E and can be found in vegetable oil, nuts and seeds. It has been suggested that it is good for the skin.

O

OH

CH3 CH3

CH3

CH3

CH3 CH3H H

CH3

CH3

Ascorbic Acid This is also known as Vitamin C and is commonly found in fruits and vegetables. It is one of the essential vitamins and the human body is unable to synthesize it. It can be easily oxidised and acts as a hydroxyl or superoxide anion radical scavenger.

OO

OHOH

OHH

OH

CH3CH3

CH3CH3

CH3

CH3CH3

CH3CH3

CH3

β-carotene

This is a precursor to vitamin A. It is a highly red-orange pigment found in plants and fruits. In particular it gives carrots their orange colour. It helps human cells to absorb vitamin A.

Soaps and Emulsions

Overview

In this section, learn about the chemistry of soap-making, find about how soaps and detergents clean, and study the chemistry of emulsions and emulsifiers.

a) Making soap

Learning intention

Find out how soaps are formed by alkaline hydrolysis of fats and oils.

SoapsSoaps are salts of fatty acids.

Alkaline hydrolysis is used to make sodium salts of fatty acids Soaps are formed by the alkaline hydrolysis of fats and oils by sodium or potassium hydroxide by boiling under reflux conditions:.

Glyceryl tristearate

+ 3NaOH + 3 Na +

Glycerol

Sodium stearate (soap)

C

C

C

O

O

O

H

H C

H C

C

H

H

O

C17

H35

O

C17

H35

O

C17

H35

C

C

C

O

O

O

H

H H

H H

H

H

H

C17H35COO --

C17H35COO --

Soap formation

This animation describes the formation of soap by the alkaline hydrolysis of fats / oils followed by neutralisation to form sodium salts of fatty acids.

The structure of soap

The long covalent hydrocarbon chain gives rise to the hydrophobic (water hating) and oil-soluble (non-polar) properties of the soap molecule (represented in yellow). The charged carboxylate group (represented in blue) is attracted to water molecules (hydrophilic). In this way, soaps are composed of a hydrophilic head and a hydrophobic tail:

COO- Na +

Hydrophobictail

Hydrophilichead

b) Cleansing action of soap

Learning intention

Learn how the characteristic structure of soap and detergent molecules allows effective cleaning of oily stains to take place.

The following ball (blue for hydrophilic head group) and stick (yellow for hydrophobic tail group) diagram represents the initial interaction of soap on addition to water and material with a grease stain:

Cleansing action of soaps

When the solution containing soap and water is agitated (stirred vigorously) the interactions of hydrophobicity and hydrophilicity become apparent. The hydrophobic, non-polar, tails burrow into the greasy, non-polar molecule – like attracting like. In the same way the polar hydrophilic head groups are attracted to polar water molecules. The head groups all point up into the water at the top of the grease stain.

The attraction of the head group to the surrounding water, via polar-to-polar interactions, is so strong that it causes mechanical lift of the grease molecule away from the material on which it was deposited. The hydrophobic tails are anchored into the grease due to non-polar to non-polar attraction. In combination, these effects allow for the removal of the grease stain.

http://www.educationscotland.gov.uk/highersciences/chemistry/animations/cleansingsoap.asp

c) Emulsions in food

Learning intention

Learn about the characteristics of an emulsion, and study the chemistry of typical emulsifier molecules.

Emulsifier moleculesAn emulsion contains small droplets of one liquid dispersed in an another liquid. Emulsions in food are mixtures of oil and water.

To prevent oil and water components separating into layers, a soap-like molecule known as an emulsifier is added. Emulsifiers for use in food are commonly made by reacting edible oils with glycerol to form molecules in which either one or two fatty acid groups are linked to a glycerol backbone rather than the three normally found in edible oils. The one or two hydroxyl groups present in these molecules are hydrophilic whilst the fatty acid chains are hydrophobic.

The presence of this emulsifier is shown on packaging by E-numbers, E471 and is one of the most common on food packaging.

Emulsifiers

Mayonnaise contains oil and water. The emulsifier keeps these mixed and without it the oil and water separate.

Emulsifiers in food

Emulsifiers in food Emulsifiers are among the most frequently used types of food additives. They are used for many reasons.

Emulsifiers can help to make a food appealing. They are used to aid in the processing of foods and also to help maintain quality and freshness.In low fat spreads, emulsifiers can help to prevent the growth of moulds which would happen if the oil and fat separated.

Emulsifiers in food

Foods that Commonly Contain Emulsifiers

Biscuits Toffees Bread

Extruded snacks Chewing gumMargarine / low fat spreads

Breakfast cereals Frozen desserts Coffee whiteners

Cakes Ice-cream Topping powders

Desserts / mousses Dried potato Peanut butter

Soft drinks Chocolate coatings Caramels

http://www.educationscotland.gov.uk/highersciences/chemistry/animations/emulsions.asp

This animation explains the difference between a stable and an unstable emulsion, and goes on to show how addition of an emulsifier can stabilise an emulsion which is otherwise unstable. The chemical structure of a typical emulsifier is described and this is used to explain the favourable properties of emulsifiers

Fragrances

Overview

In this section, learn about the chemistry of terpenes and essential oils, key components of fragrances.

a) Essential oils

Learning intention

Learn about the constitution, properties and uses of essential oils.

Essential oils

• Essential oils are the concentrated extracts of volatile, non-water-soluble aroma compounds from plants.

• Essential oils are widely used in perfumes, cosmetic products, cleaning products and as flavourings in foods.

Essential oils

• Essential oils are mixtures of organic compounds.

• Terpenes are the key components in most essential oils.

The history of essential oils

• The benefits of essential oils have been recognised for thousands of years.

• Their use is described in the New Testament of the Bible.

• They were used in anointing rituals and in healing the sick.

The history of essential oils The ancient Egyptians used essential

oils for embalming, religious rites and medicinal purposes.

King Tut’s tomb was found to contain 50 jars of essential oil when it was opened in 1922.

Modern uses

Essential oils

Cosmetics Flavours

Perfumes Medical

Cleaning

Insect repellents

Dentistry Adhesives

What are essential oils?

• ‘Essential’ refers to the fact that the oil carries the distinctive essence (scent) of the plant.

• Concentrated, volatile, non-water soluble aroma compounds extracted from plants.

• Contain no artificial substances, unlike perfumes and fragrance oils.

Essential oils – composition

• Essential oils are mixtures of organic compounds.

• Terpenes are the key components of all essential oils.

Essential oils – chemistry

• The distinctive character of an essential oil can be attributed to the functional group present in its key molecule.

• Esters, aldehydes, ketones and alcohols are all found in essential oils.

Essential oils – perfume

• The ester linalyl acetate is found in the essential oil lavender.

• This ester is often added to perfumes.

CH3

CCH

CH2CH2

CCH

CH2

O

C

CH3

O

CH3CH3

Linalyl acetate

Essential oils – cleaning

• The essential oil known as lemon oil contains the terpene d-limonene.

• It is known for its ability to act as a natural solvent and a cleanser.

CH2

CH2C

CH

CH2

CH

CCH2CH3

CH3

Limonene

(skin of citrus fruits)

Hospital cleaners

• Certain essential oils kill bacteria and fungi (including MRSA and E. coli) within 2 minutes of contact.

• Essential oils are blended into soaps and shampoos used in hospitals to eradicate deadly ‘super bugs’.

Essential oils – cosmetics

• The essential oil geraniol is added to some cosmetics to balance and revitalise the skin.

CH3

CCH

CH2CH2

CCH

CH2OH

CH3CH3

Geraniol

Essential oil – cold sores

• Melissa oil contains the terpene citral, which is used to combat cold sores.

CH3

CCH

CH2CH2

CCH

CO

HCH3CH3

Citral

Essential oils – toothpaste• The essential oil thymol has antiseptic properties.

CH

CHC

C

CHC

CH3

OH

CHCH3 CH3

Thym ol

Steam distillation• Steam distillation is one of the methods used to

extract essential oils from plants.

• Steam passes over the plant and extracts the essential oil.

• The mixture evaporates and passes into the condenser.

• The essential oil vapour is chilled and collected.

Steam distillation

Essential oils – summary

• Concentrated extracts of volatile, non-water-soluble aroma compounds from plants.

• Widely used in perfumes, cosmetics, cleaning products and flavourings.

• Mixtures of organic compounds.

• Terpenes are the key components of most essential oils.

b) Terpenes

Learning intention

Learn about the chemistry and uses of terpenes, a key group of unsaturated molecules based upon isoprene.

Terpenes

• The name ‘terpene’ is derived from the Greek word ‘terebinth’.

• Terebinth is a type of pine tree from which terpene-containing resins are obtained.

What are terpenes?

• Natural organic compounds.

• Components of a variety of fruit and floral flavours and aromas.

• Used in perfumes, essential oils and medicines.

Essential oils contain terpenes

• Lavender – used to relieve tension.

• Ylang-ylang – used to treat anxiety.

• Lemon oil – aids good circulation.

• Essential oils often contain a mixture of terpenes.

Spices contain terpenes

• Terpenes in plants can be oxidised to produce the compounds responsible for the distinctive aroma of spices.

• Terpenes containing oxygen or other functional groups are known as ‘terpenoids’.

• Common spices containing terpenes include cloves, cinnamon and ginger.

Terpenes are unsaturated

• Terpenes are unsaturated compounds.

• All terpenes are built up from units of isoprene.

Isoprene

• Isoprene is the common name for

2-methylbuta-1,3-diene

CH2

C CH

CH2CH3

CH2 C CH CH2

CH3

Isoprene

C

CH3

CH2

CH

CH2

Head Tail

Isoprene(2-methylbuta-1,3-diene)

=

One isoprene unit contains five carbon atoms

Building terpenes from isoprene

Isoprene units can be linked:

• head to tail to form linear terpenes

• in rings to form cyclic terpenes.

Myrcene – a linear terpene

• Myrcene is a component of plants, including bay, ylang-ylang and thyme.

Head Tail

C

CH3

CH2

CH

CH2

Head Tail

C

CH3

CH3

CH

CH2

C

CH2

CH2

CH

CH2

C

CH3

CH2

CH

CH2

Limonene – a cyclic terpene

CH2

CH2C

CH

CH2

CH

CCH2CH3

CH3

Limonene

(skin of citrus fruits)

Menthol – a cyclic terpenoid

CH2

CHCH

CH2CH

CH2

CH3

OH

CHCH3CH3

Menthol

(peppermint)

This terpene has been oxidised to a terpenoid

Absinthe – a cyclic terpenoid

CH2

C

CHCH

C

CH2

O

CH3

CHCH3CH3

Thujone

(Absinthe)

This terpene has been oxidised to a terpenoid

Camphor – a cyclic terpenoid

CH2

CH2

CH

C

CC

CH2

OCH3

CH3CH3

Camphor

(Camphor tree)

-Selinene – a cyclic terpene

3 isoprene units

15 carbon atoms

CH2

CH2CH2

CHC

CH2

CH3

C

CC

CH2

CH2

CH2

CH2

CH3

H

-Selinene

β-carotene – a linear terpene

8 isoprene units

40 carbon atoms

CH2

CH2

CH2C

CC

CH3CH3

CHCH

CCH

CHCH

CCH

CHCH

CHC

CHCH

CHC

CHCH

CC

CH2

CH2CH2

CCH3

CH3 CH3CH3 CH3

CH3CH3

CH3

-carotene

Questions

• Which unit makes up every terpene?

• How many carbons are there in an isoprene unit?

• What is the systematic name for isoprene?

• What is an oxidised terpene known as?

Answers

• Which unit makes up every terpene?Isoprene unit

• How many carbons there are in an isoprene unit?Five

• What is the systematic name for isoprene?2-methylbuta-1,3-diene

• What is an oxidised terpene known as?Terpenoid

Summary

• Terpenes are unsaturated compounds formed by joining together isoprene units.

• Terpenes are components in a wide variety of fruit and floral flavours and aromas.

• Terpenes can be oxidised within plants to produce the compounds responsible for the distinctive aroma of spices.

Skin care products

Overview

In this section, learn about the effect of UV-light on the skin, including the chemistry of free-radical reactions and the role of UV-scavengers in skin-care products.

a) Effect of ultra-violet light

Learning intention

Learn how high energy UV-light causes damage to skin by breaking bonds in molecules.

Sun, sea, sand and ….

• Ultraviolet radiation is broken into three types of wavelengths:

• UV-A: This is the longest wavelength and is not absorbed by the ozone. It penetrates the skin deeper than UV-B.

• UV-B: Responsible for sunburns. It is partially blocked by the ozone layer.

• UV-C: This is totally adsorbed by the earth's atmosphere; we encounter it only from artificial radiation sources.

Image of the sun taken with ultraviolet imaging telescope

Ultraviolet radiation (UV)

Ultraviolet radiation (UV)

Ultraviolet radiation (UV) is a high-energy form of light, present in sunlight. Exposure to UV light can result in molecules gaining sufficient energy for bonds to be broken.

UV damage to DNA

Damage to DNA causes mutations which stop the DNA functioning properly

The radiation excites DNA molecules in skin cells, causing new covalent bonds to form between adjacent cytosine bases, producing a bulge. This mutation can result in cancerous growths, and is known as is commonly seen in skin cancers.

Skin cancer – malignant melanoma

In the UK, 2,000 people a year die from malignant melanoma, and the number is increasing.

Natural defence - Melanin

Melanin is a pigment that is produced when your skin is exposed to sunlight. It absorbs the UV radiation found in sunlight to help protect your skin. This results in your skin becoming darker, a tan which is a sign that it has been damaged by UV rays.

Melanin stops you burning so easily but it does not prevent the other harmful effects of UV radiation, such as cancer and premature ageing.

Photo ageing

• In the skin, UV radiation causes collagen to break down.

• The body tries to rebuild the collegen, disorganized collagen fibers known as solar scars can form.

• When the skin repeats this imperfect rebuilding process over and over wrinkles develop.

There’s no such thing as a healthy tan

Photoageing caused by UVA

Exposed to sun Not exposed to sun (through car window)

TAXI Driver

The effects of UV - ageing of skin

How to protect yourself-Sunscreen

Sunscreen works by combining organic and inorganic active ingredients.

Inorganic ingredients like zinc oxide or titanium oxide reflect or scatter ultraviolet (UV) radiation.

Organic ingredients adsorb UV radiation, dissipating it as heat.

UV photography reveals sun damageThis article illustrates how dermatologists use ultraviolet (UV) photography to show their patients how the sun has damaged the skin.

Your health, your choices: SunburnNHS information on sunburn, including symptoms, causes, treatment and prevention.

SunblockGuidance from the School of Medicine at the University of California, San Francisco, on the use of sunblock to prevent skin cancer. Lists common active ingredients of sunblock.

AcknowledgementsAcknowledgements

AcknowledgementsAcknowledgements

ReferencesReferences

ReferencesReferences

ConclusionsConclusions

ConclusionsConclusions

PurposePurpose

PurposePurpose

MethodsMethods

MethodsMethods

ResultsResults

ResultsResults

IntroductionIntroduction

IntroductionIntroduction

UV Radiation and Children: A study of sunglass use UV Radiation and Children: A study of sunglass use to prevent ocular damage from sun exposure to prevent ocular damage from sun exposure

UV Radiation and Children: A study of sunglass use UV Radiation and Children: A study of sunglass use to prevent ocular damage from sun exposure to prevent ocular damage from sun exposure

M. Bauer, W. Catanio, W. Fahrman, B. Godard, R. Irwin, A. M. Bauer, W. Catanio, W. Fahrman, B. Godard, R. Irwin, A. OpydOpyd

New England College of Optometry, Boston, MANew England College of Optometry, Boston, MA

M. Bauer, W. Catanio, W. Fahrman, B. Godard, R. Irwin, A. M. Bauer, W. Catanio, W. Fahrman, B. Godard, R. Irwin, A. OpydOpyd

New England College of Optometry, Boston, MANew England College of Optometry, Boston, MA

Up to 80% of a lifetime sun exposure is obtained before the age 18. Children require special protection as they are at the highest risk for developing ocular damage or diseases caused by overexposure to Ultraviolet radiation from sunlight.

Acute eye damage can occur from single outings on bright days. Photokeratitis, (solar corneal damage) is a temporary but painful burn on the surface of the eye (cornea). This self-healing injury typically resolves in 24 hours with no permanent damage.1

Chronic UV exposure contributes to the development of many eye disorders: Pterygium is an abnormal growth of fibro-vascular tissue from the corner of the eye. If severe, a pterygium can grow over the cornea, threatening vision loss and requires surgery to be removed; Cataract is a clouding of the normally clear, natural lens inside the eye. The clouded lens prevents light from reaching the retina therefore reducing vision; Skin Cancer can develop on the eyelids and surrounding skin. Basal cell carcinomas, squamous cell carcinomas, and malignant melanomas can all occur from chronic UV exposure2,3 (Figure 1).

It is important that parents teach their children how to enjoy fun in the sun safely. With the right precautions, the chance of developing ocular damage can be greatly reduced. It has been proven that simple measures, such as the use of brimmed hats and sunglasses, as personal protection measures can effectuate up to an 18-fold difference in ocular UV exposure.2

To determine if children are wearing sunglasses regularly.

To investigate whether or not parents are aware of the harmful effects of UV radiation on young children's eyes.

A six-item survey was composed to access parental knowledge and awareness of the adverse effects of sunlight on the eyes. The surveys were handed out, with permission, at an elementary school and a pediatrician’s office in New Jersey and Rhode Island. Different states were surveyed in order to make the results generalizable throughout the United States. Results of the survey were analyzed in order to determine if public education would be beneficial to this issue. An educational pamphlet was made in order to inform the public on the negative effects of sunlight on the eyes.

Of the 800 surveys distributed, 235 were returned and analyzed. Parental educational background of those surveyed included college 57%, high school/GED 21%, graduate/masters 18%, and some high school 4%. When asked if they always, sometimes, or never wore sunglasses it was found that the majority of parents sometimes wore sunglasses. It was also found that the majority of their children sometimes wore sunglasses (Figure 2,3).When asked if their child would wear sunglasses if given a pair, 76% said yes. The majority of parents felt that childhood was the ideal age to start wearing sunglasses, with 75% of the responses. It was found that the majority of the people surveyed knew that UV radiation was damaging to the eyes (figure 4). Of these parents 50% were unable to provide a correct possible outcome. The top three incorrect answers were blindness, glaucoma, and sensitivity/squinting/soreness. The top three obtained correct answers were cataract, damage to retina, and damage to cornea.

Despite the public consciousness of UV damage there has been little public education involved in the prevention of cataracts, pterygia, or photokerititis. The most obvious and cost effective form of prevention is the use of sunglasses. 4 Sunglasses are available in various styles and sizes, with 100% UV protection, at low cost.

The segment of the population at greatest risk to accrue damage from ultraviolet radiation is children from the ages of birth to adolescence. UV absorption by the natural lens of the eye varies throughout life. Immediately after birth, nearly all of the UV light is transmitted by the lens. During childhood, lens transmittance decreases, and by the age of 25, the lens absorbs UV light almost completely.2 Regardless of the fact that an overwhelming number of parents thought that childhood was the ideal age to start wearing sunglasses, only 11% answered that their children always wore sunglasses. Children’s lack of wearing sunglasses could be due to the fact that manufactures and advertisement companies are not

using this age group as a demographic target. The most

common answer of why children would not wear sunglasses was that they found them uncomfortable. More research on the design of children’s sunglasses could be beneficial to this issue.

In conclusion, there is a serious lack of education on the damaging ocular effects of sun exposure. Moreover, there is little preventative behavior in preventing these potentially serious diseases. Because it is known that sunglass protection is most vital in childhood, it is alarming to see that a majority of youth are not protecting their eyes.

This preliminary survey showed that there is a potential need for public health education on the adverse effect of UV radiation on the eye and the protection methods that could possible prevent these effects. A larger scale survey would be beneficial to determine nation wide parental knowledge on this subject. Future research would determine the most effective educational program. In order to aid the education process an ocular sun safety flyer will be distributed to optometric offices across the state of Massachusetts. 1. Cronly-Dillon, J, Rosen, E. S., & Marshall, J. Hazards of light : myths &

realities : eye and skin : proceedings of the First International Symposium of the Northern Eye Institute. University of Manchester, July 1985.

2. Friedlaender, Mitchell. Ultraviolet Radiation and the Eye. International Ophthalmology Clinics. 2005;45:49-52

3. Parisi, Alfio V., Green, A., & Kimlin, M. G. Diffuse Solar UV Radiation and Implications for Preventing Human Eye Damage. Photochemistry and Photobiology. 2000;73:135-139.

4. Van Kuijk J.G.M, Frederik. Effects of Ultraviolet Light on the Eye: Role of Protective Glasses. Environmental Health Perspectives. 1991;96:177-184

5. Ocular Image Database, New England College of Optometry Library [Internet]. [Cited 2006 Apr 26]. http://ncoimagesdb.ne-optometry.edu/ocular.asp.

6. Basal Cell Carcinoma (BCC), University of Utah John A. Moran Eye center [Internet]. [Cited 2006 Apr 26]. http://www.insight.med.utah.edu/opatharch/lid/basal_cell_carcinoma_bcc.htm.

A special thank you to Dr. Clifford Scott and Dr. Li Deng for their help with this public health project.

Frequency of sunglass wear in children

25.0 28.9

55.6

56.365.3

38.9

18.8

5.65.8

0.0

20.0

40.0

60.0

80.0

100.0

120.0

Parent Always ParentSometimes

Parent Never

Parental sunglass use

% o

f chi

ldre

n th

at w

ear

sung

lass

es

Child Always

Child Sometimes

Child Never

Comparative amount of sunglass use in children and parents

0

20

40

60

80

100

120

140

160

Never Sometimes Always

Amount

Num

ber

of r

espo

nses

parents

children

Results cont’dResults cont’d

Results cont’dResults cont’d

Figure 1. Ocular disease manifestations.

Figure 4. Parental awareness of ultraviolet radiation damage to the eye.

Figure 2. The comparison of children and adult sunglass wear.

UV damage awareness

Yes realistic28%

Yes false50%

No22%

Figure 3. Percent of children that wear sunglass in relation to parental use.

According to the results found in the previous section, 78% of adults surveyed were aware that ultraviolet radiation is damaging. However, half of them where unaware of the actual pathologies involved. The severity of sun exposure was also greatly underestimated. Common incorrect answers were blindness, glaucoma, watery eyes, and wrinkles. These general trends lead to several possible conclusions. One being that further education is a possible solution to the lack of adequate sunglass use.

Conclusions cont’dConclusions cont’d

Conclusions cont’dConclusions cont’d

a. UV damage to cornea5

b. Pterygium5

c. Cataract5 d. Skin cancer6

b) Free radical reactions

Learning intention

Study the chemistry of free radical chain reactions.

Hydrogen and chlorine

  

 

When UV light breaks bonds free radicals are formed.Free radicals have unpaired electrons and, as a result, are highly reactive. Free radical chain reactions include the following steps: initiation, propagation and termination.

Hydrogen and chlorine

  

 

1) Initiation

U.V. light provides the energy for the homolytic fission of halogen into reactive halogen atoms or free radicals (atoms with an unpaired electron).

Cl2(g) → Cl.(g) + .Cl(g)

Hydrogen and chlorine

  

 

2) Propagation

In this stage, free radicals collide with other species but the number of free radicals is maintained (hence the term propagation).

H2(g) + .Cl → H.(g) + HCl(g)

H.(g) + Cl2(g) → HCl(g) + Cl. (g)

These reactions continue until reactants are used up, or until free radicals are used up by collision with each other.

Hydrogen and chlorine

  

 

3) Termination In this stage, free radicals are used up by collision with each other.

H.(g) + .Cl(g) → HCl(g) H.(g) + .H(g) → H2(g)

Cl.(g) + .Cl(g) → Cl2(g)

Free radical Substitution Methane

Another free radical reaction takes place when halogen is substituted into an alkane in the presence of UV light. This reaction is not explosive and results in the decolourisation of bromine.  Alkanes react with bromine in the presence of U.V. light, though the reaction with bromine is slow. The reaction can be shown as follows:

CH4(g) + Br2(g) → CH3Br(g) + HBr(g)

The presence of acid HBr in the product can be shown with moist pH paper. However, the reaction does not end here and further substitution can occur with hydrogen atoms progressively replaced by halogen atoms.

The slow substitution reaction follows a free radical chain reaction, initiated by U.V. light (hν). For convenience, the reaction can be split into three stages.

Free radical Substitution Methane

1) Initiation U.V. light provides the energy for the homolytic fission of halogen into reactive halogen atoms or free radicals (atoms or molecular fragments with an unpaired electron).

Br2(g) → Br.(g) + .Br(g)

Free radical Substitution Methane

2) Propagation In this stage, free radicals collide with other species but the number of free radicals is maintained (hence the term propagation).

CH3-H(g) + .Br → CH3.(g) + HBr(g)

CH3.(g) + Br2(g) → CH3 - Br(g) + Br. (g)

These reactions continue until reactants are used up, or until free radicals are used up by collision with each other.

Free radical Substitution Methane

3) Termination In this stage, free radicals are used up by collision with each other.

Br.(g) + .Br(g) → Br2(g) CH3

.(g) + .Br(g) → CH3 - Br(g) CH3

.(g) + .CH3(g) → CH3 - CH3(g) The product of the last equation is ethane. However, to minimise the range of possible products, an excess of the original alkane is used and the products separated from the excess alkane by distillation.

Free radical Substitution Methane

Evidence to support this mechanismThe reaction is initiated by U.V. light and, once started, can continue in the dark. Other substitution products are made such as CH2Br2, CHBr3, CBr4 together with longer alkanes (and smaller amounts of substitution products of these alkanes.However, these other substitution products can be minimised by using an excess of the original alkane to try to ensure collision of the relatively small number of free radicals produced by sunlight quickly uses up the bromine.

c) Free-radical scavengers

Learning intention

Learn about the chemistry of the free-radical ‘scavenger’ molecules which are included in many skin-care products.

Free Radical ScavengersMany cosmetic products contain free radical scavengers.These are molecules which can react with free radicals to form stable molecules and prevent chain reactions. Melatonin and Vitamin E are examples of natural free radical scavengers.

MelatoninFree radical scavengers are also added to food products and to plastics.As UV light can cause wrinkling of skin, some skin-care products claim to contain chemicals which prevent wrinkling. These are claimed to be anti-aging creams. Free radicals remove electrons from skin cells and damage them and wrinkles start to develop.

• Here is a banned advert. This time Nivea Visage is suggesting that the cream could deliver permanent benefits

Do they work?There is a range of antioxidants used in anti-wrinkle creams, and some are better at penetrating the skin than others. The antioxidants used in skin care are derived from Vitamins A, E and C

The derivatives of Vitamins A (retinol) and E combat free radicals. Vitamin C is used in the construction of collagen. Other antioxidants work by exfoliating the dead skin on the surface to reveal newer, younger-looking skin underneath. Still others create a barrier to prevent moisture loss fromClaims for retinol derivatives say it can reduce the appearance of lines and reduce skin roughness, and blotchiness. There is some research that says retinol can increase the thickness of the epidermis. But as the molecules are large, they can't fit though the skin unless combined with substances that make the holes in the lipid matrix bigger. Vitamin E is the most widely used ingredient in skin care products, used for its moisturising and antioxidant properties.

Predicting Physical Properties of Molecules from Functional

GroupsLearning intentions

To become familiar with identifying key functional groups within molecules.

To be able to explain the influence of functional groups on intermolecular forces.

To be able to predict the physical properties of molecules from functional groups present.

Butanoic acid has a powerful, unpleasant odour. It is found in rancid butter, Parmesan cheese and vomit.

Can you identify and name the functional group present in butanoic acid?

Carboxyl group

Aqueous solutions of methanal are commonly used in embalming to preserve human or animal remains.

Can you identify and name the functional group present in methanal?

Carbonyl group

Is methanal an aldehyde or a ketone? Aldehyde

The molecule below is found in the disinfectant Dettol, which we instantly recognise by its distinctive smell. Dettol (chloroxylenol) helps us fight unwanted bacteria.

Can you identify and name the functional group present in Dettol?

Hydroxyl group

Carboxyl group

Amide group

4-formamidobenzoic acid is used in pharmaceutical compositions.

Can you identify and name two functional groups present on the 4-formamidobenzoic acid molecule?

Cinnamon is a tasty spice used to flavour biscuits, cakes and pies. Cinnamon also has medicinal properties.

Can you identify and name two functional groups in cinnamon?Is cinnamon an aldehyde or a ketone?

Carbonyl group

Carbon-to-carbon double bond

Aldehyde

What is the strongest type of intermolecular force of attraction between cinnamon molecules?

(Hint: Think about the bond polarity of the functional groups present!)

Can you identify and name the two functional groups present in methyl anthranilate?

Amino group

Methyl anthranilate occurs naturally in grapes and is used as grape flavouring in drinks and chewing gum.

Ester link

Can you identify and name three different types of functional group on the structure of vitamin C?

Ester link

Hydroxylgroup

Vitamin C is needed in your diet for the growth and repair of tissues in all parts of your body.

Carbon-to-carbon double bond

Which is the strongest type of intermolecular force of attraction between molecules of vitamin C?

Is vitamin C a polar or a non-polar molecule?

Is vitamin C soluble in water or in hexane?

(Hint: Think about which functional groups are present!)

Glucose is a simple sugar that is used as an energy source by many living organisms.

Is glucose soluble in water or in hexane? Justify your answer with reference to the functional groups present.

2-methylpropane is a branched hydrocarbon that is used as a refrigerant.

Is 2-methylpropane soluble in water or in hexane? Justify your answer with reference to the structure.