Organic Chemistry

Organic Chemistry: Carbon Compound Chemistry

• Organic chemistry is the chemistry of carbon compounds. Originally these were compounds that were studied from organisms.

An Early Perspective on Organic Chemicals• In Organic chemistry’s early stages, chemists wondered if

chemicals from living things had some special properties or life force associated with them.

• The compound, urea , was isolated from human urine. To show it was just a regular chemical without special life properties, Wohler (a German chemist) made urea from scratch in a chemical laboratory.

Hydrocarbons• Hydrocarbons are compounds of just carbon and

hydrogen.

Hydrocarbons

• Many hydrocarbons are produced by fractional distillation of crude oil.

Alkanes: Single Bonds• Hydrocarbons with only single bonds between all carbon

atoms are called alkanes.

Alkanes: General Formula

• The general formula for alkanes is CnH2n+2 .

Bond Number in Hydrocarbons• In any organic compound, every C atoms always has 4

bonds, every H atom always has 1 bond, every O atom always has 2 bonds, every halogen atom (F, Cl, Br, I) always has 1 bond and every N atom always has 3 bonds.

Alkane Nomenclature

Alkane Boiling Points• As the hydrocarbon chains gets longer, the boiling points

increase due to increasing London forces between the increasingly longer molecules.

Branched Alkanes• Alkanes can have many branches coming off a main chain.

Side Chain Groups• If a hydrogen atom is detached from an alkane chain, it

becomes a group that can be attached to another alkane chain.

• A methyl group is a methane minus a hydrogen atom.• An ethyl group is an ethane minus a hydrogen atom.

Alkane Nomenclature1. Number the longest carbon chain so that side groups get

the lowest numbers.

2. Use numbers followed by commas and dashes to indicate group locations and names. Below is 3,3,6-trimethylheptane :

Alkane Nomenclature1. Number the longest carbon chain so that side groups get

the lowest numbers.

2. Use numbers followed by commas and dashes to indicate group locations and names.The left structure is 1,3-dichlorohexaneThe right structure is 2,3-dichloropentane

Alkane Nomenclature1. Number the longest carbon chain so that side groups get

the lowest numbers.

2. Use numbers followed by commas and dashes to indicate group locations and names. The side groups are listed alphabetically: ethyl before propyl.

Below is 3-ethyl-4,5-dipropyloctane.

Alkane Nomenclature1. Number the longest carbon chain so that side groups get

the lowest numbers.

2. Use numbers followed by commas and dashes to indicate group locations and names (alphabetic order).Below is 4,6-diethyl-4,6,7-trimethyl-5,5-dipropyldecaneNot 5,7-diethyl-4,5,7-trimethyl-6,6-dipropyldecane

Isomers• Isomers are organic compounds which have the same

chemical formula but have different structures and properties.

• The isomers of C5H12 are shown

Isomers• Isomers are organic compounds which have the same

chemical formula but have different structures and properties.

• The isomers of C6H14 are shown

Cycloalkanes• Alkane rings are called cycloalkanes. Their general

formula is CnH2n .

Cycloalkanes• Cycloalkanes can have groups and are numbered so that

the groups get the lowest numbers as with alkane chains.

Alkenes• Alkenes are hydrocarbons

with one or more double bonds.

• Alkenes are named by the numbers of carbon atoms like alkanes but with an “ene” ending.

• The last three structures to the right shown require an extra H at the rt. End of the molecule.

• Alkenes have a general formula, CnH2n .

Alkene NomenclatureSome alkenes can have their double bonds in numerous

positions so their naming system accounts for the double bond placement.

The Geometry of Alkenes

• Unlike alkanes in which atoms can freely rotate, in alkenes the double bond rigidly fixes atoms on either side of the double bond.

Cis-Trans Isomers

• In alkenes with groups other than hydrogen, two different molecules are possible with the same formulas. Trans isomers have the groups diagonally opposite while cis isomers have the groups on the same side of a molecular axis.

Cis and Trans 2-Pentene• The groups on opposite sides of the double bond in 2-

pentene are in different positions so these molecules are isomers

Alkene NomenclatureSome alkenes can have their double bonds in numerous

positions so their naming system accounts for the double bond placement. But-1-ene can be called n-butene or 1-butene.

Alkynes• Alkynes have one or more triple bonds. They are named

by using the standard alkane root and applying a “yne” ending rather than the “ane” ending.

Triple Bond Position Alters an Alkyne’s Name

Like alkenes, alkynes need to have their triple bond position notated in their name.

General Formula for an Alkyne

The general formula for an alkyne is CnH2n-2 .

The Geometry of Alkynes• The triple bond of an alkyne is very rigid. Parts of alkynes

with repeating triple bonds form straight, needle-like molecules.

Comparison of Single, Double and Triple Bonds

• The length of a bond shortens from single to double to triple bonds.

Benzene – A Ring Compound• Benzene, C6H6 , is a common organic molecule.

Benzene’s Bond Lengths• Although benzene can be constructed with alternating double

and single bonds, every bond between the carbons is midway between a single and a double bond.

Explaining Benzene’s Intermediate Bond Length

• A concept called resonance is used to explain the intermediate bond length of benzene’s bonds.

• Resonance is the idea that the double bonds alternate between the atoms which evens out the sharing of electrons, bonds of intermediate length.

Resonance in Benzene

• Different resonance structures show alternating double bonds.

Ways of Representing Benzene

Aromatic Compounds• Any compound incorporating the benzene ring is

called an aromatic compound.

Many Aromatic Compounds have Aromas

• Spearmint smell

Steroid Molecules are Aromatics

Functional Groups• A functional group is a specific group of atoms on a

molecule that gives it specific properties.

Alcohols• All alcohols have one or more hydroxyl groups (-OH)• The General Form of an alcohol is R-OH, where R stands for any

organic chain or ring.

Naming Alcohols

• The molecule above is 3-methyl-2-pentanol• Alcohols take the longest chain name, replacing the

regular ending with an –ol ending.

Properties of Alcohols• Alcohols have an –OH group (polar character) that makes them

more soluble in water but they may also have longer hydrocarbon chains (nonpolar character) which make them less soluble in water.

Review of Polar Molecules• Water is a polar molecule (develops + and – poles) because

the oxygen atom attracts shared electrons more than hydrogen does.

Polar Water Molecules Attract Polar Substances

• Water, a polar substance will dissolve other polar substances or substances with charged particles.

The “Like Dissolves Like” Rule• Nonpolar substances (like gasoline) dissolve and mix with

(are soluble in) nonpolar substances while polar substances are soluble with polar substances.

Polar and Nonpolar Substances are Immiscible (Do Not Mix)

Properties of Alcohols

• If the –OH group is more prominent than the carbon chain, the alcohol is soluble (methanol, ethanol and propanol). If the chain is more prominent, the alcohol resists dissolving in water (butanol, pentanol etc.)

Other Alcohol Properties• All alcohols are poisonous

• Ethanol (in beer, wine and spirits) is less poisonous but slows down the nervous system and shut down the brain and breathing. When drunk persons pass out, they may stop breathing. The liver detoxifies ethanol.

The Aldehyde and Ketone Functional Group

• The carbonyl group converts an organic compound into either an aldehyde or a ketone, depending on whether the group is on an end carbon or a carbon within a chain.

A Carbonyl Group on an End Carbon, makes an Aldehyde

• An aldehyde changes the root name to –al.• Methanal (commonly called formaldehyde), ethanal, and

propanal are three aldehydes.

An Aromatic Aldehyde

• Benzylaldehyde is formed from benzene and an attached carbon with carbonyl group.

Ketones Made by Internal Carbonyl

• Ketones have a carbonyl group on a carbon not on the end of a molecule.

• Ketones change the regular chain ending to -one

Naming Ketones• Besides changing the

ending to –one, the position of the carbonyl group must be indicated.

• 3-pentanone

The Organic Acid Group

• Carboxyl groups (-COOH) attached to an organic molecule give the molecule an acidic character.

Naming Organic Acids

• Organic Acids change the root name ending to –oic acid. (methanoic, ethanoic, propanoic acids)

Methanoic Acid (Formic Acid)

• Ants use formic acid as a defense or stunning chemical against predators or prey.

Ethanoic Acid (Acetic Acid)

• The active ingredient of vinegar is acetic acid, usually present in about 5% by volume.

• Vinegar is often manufactured from ethyl alcohol in wines or ciders.

Other Organic Acids with COOH Group(s)

The Ether Linkage

• The oxy group makes ethers of organic compounds.

Naming Ethers

• The shortest hydrocarbon chain prefix is used with oxy followed by the longer chain hydrocarbon name unchanged.

• Methoxypropane

Branched Chain Ethers

• When naming branched chained ethers, the carbons on the chains are numbered from the oxy group.

• The formula for 1-methoxy-3,3-dimethylbutane

is CH3OCH2CH2C(CH3CH3)CH3

Properties of Ethers

• Ethers have low boiling points, evaporating readily.• Ethers have anaesthetic properties, rendering higher

organisms unconscious, “quieting” lower organisms.

The NH2 Group and Amines

• An amine is an organic compound containing an NH2 group.

• Amines often have “fish-like” odour.

Amino Acids

• Amino acids have an amine group and an acid group.

Amino Acids

• Living things make and use amino acids. There are 20 naturally-occuring amino acids.

• A

Amino Acids

• Amino acids link together to form long chains that become proteins, very important compounds in living things.

Bonding of Amino Acid

• When amino acids are bonded together, they lose a water molecule, so this type of reaction is called a condensation synthesis

Amino Acids

• The bond between amino acids is called a peptide bond and a chain of amino acids is called a polypeptide

Amino Acid Bonding

• The linkage between amino acids (peptide bond) is generally known as an amide linkage

• The oxygen in the above structure should have a double bond !

Amides

• Amides have the amide group, CONH2

• Amide chains are numbered from the amide group

• A

The Ester

• An ester is an organic compound in which a COO group joins two hydrocarbon chains.

The Ester

• Esters often have distinct aromas and flavours.

Alcohols and Acids React, Forming Esters

• In naming an ester, the alcohol chain is given a –yl ending followed by the acid chain name whose ending becomes –ate.

Examples of Esters

• Rum is isobutyl propionate Pear is propyl formate• Apple is methyl butyrate Orange is octyl acetate• Banana is 3-methyl butylacetate

Triglycerides (Fats) and the Ester Linkage

• Fatty acids are linked to glycerol by means of ester linkages.

Summary of Functional

Groups

• Groups not represented include esters and ethers

• A

Summary of Functional Groups

Organic Reactions: Oxidation and Reduction

• Organic molecules are oxidized if they have oxygen added to the molecule or if they have hydrogen removed from the molecule

• Alcohol in wine is oxidized to ethanal and then to acetic acid (Wine in air or acted on by aerobic bacteria turns to vinegar).

Substitution ReactionsSubstitution reactions occur with alkanes. One

atom or group on a chain is substituted with another.

+ Cl-Cl + H-Cl

Multiple SubstitutionsWhen chlorine gas is reacted with methane, Cl

atoms can substitute up to four hydrogens.

+ Cl-Cl + H-Cl

chloroform

Displacement ReactionsOne group can take the place of another and this is

called a displacement reaction.

+ NH3 + H-Cl

Addition ReactionsIn alkenes, a double bond can be opened, leaving

two sites for the parts of another substance to bond to. Alkenes are more reactive than alkanes.

+ H-O-H

Examples of Other Addition Reactions

Polymerization Reaction (Forming Plastics)A monomer is a repeating unit found within a larger

molecule. A polymer is a molecule made up of similar repeating monomers. Polymerization is the reaction in which monomer link together to form polymers.

Addition Polymerization ReactionsAddition polymerization involves the bonding of polymers

without the elimination of atoms. Molecules with double bonds open one of the bonds which allows them to link together in a long chain. The monomer ethene opens one of its double bonds to form a long polymer, polyethylene.

+

Addition Polymerization ReactionsAddition polymerization involves the bonding of polymers

without the elimination of atoms. Molecules with double bonds open one of the bonds which allows them to link together in a long chain. The monomer ethene opens one of its double bonds to form a long polymer, polyethylene.

Teflon Addition PolymerTeflon is a plastic (polymer) used for valves and

non-stick surfaces.

Saran Addition Polymer

Lucite Addition Polymer

Plexiglass Addition PolymerA

PVC Addition PolymerA

Styrofoam Addition PolymerA

Condensation Polymerization ReactionsCondensation polymerization results in the

elimination of atoms, often water molecules.

Protein

Dacron (A Polyester) :Condensation Polmerization

ElastomersA

Thermoplastic PlasticsA

Thermosetting PlasticsA

AA

AA