chapter 18 : organic chemistry

Chapter 18 : Organic Chemistry

Organic chemistry:The study of the compounds of carbon.

• 85% of all known compounds are organic.

• Carbohydrates, lipids, proteins, enzymes, nucleic acids, hormones, vitamins, and almost all other chemicals in living systems are organic compounds.

C

< Abundance of the elements in the Earth’s crust.

Why is organic chemistry a separate discipline within chemistry?Vitalism: a “vital force” present in living organisms was believed to be necessary to produce an organic compound.

The experiment of Wöhler in 1828 was the first in a series of experiments that led to the demise of the vital force theory. See reaction below:

NH4Cl AgNCO H2N-C-NH2

OAgCl+ heat +

Ammoniumchloride

Silvercyanate

Urea Silverchloride

Why are Organic Compounds and Inorganic Compounds Different?

• carbon atoms can do some unique things that other atoms cannot

• their bonds are very strong and unreactive• they can attach together in very long chains• they can attach together to form rings• they can form single, double or triple bonds

Hydrocarbons• hydrocarbons contain only C & H• two types - aliphatic or aromatic• insoluble in water

– no polar bonds to attract water molecules• aliphatic hydrocarbons

– may be chains or rings• ring molecules have two less H than chain so that ends

can join• straight chain called the “normal” isomer

Saturated Hydrocarbons

• a saturated hydrocarbon has all C-C single bonds– it is saturated with hydrogens

• saturated aliphatic hydrocarbons are called alkanes

• chain alkanes have the general formula CnH2n+2

Unsaturated Hydrocarbons• unsaturated hydrocarbons have one of more C=C

double bonds or CC triple bonds• unsaturated aliphatic hydrocarbons that contain C=C

are called alkenes– the general formula of a monounsaturated chain alkene is

CnH2n

– remove 2 more H for each additional unsaturation• unsaturated aliphatic hydrocarbons that contain CC

are called alkynes– the general formula of a monounsaturated chain alkyne is

CnH2n-2

– remove 4 more H for each additional unsaturation

Hydrocarbons

8

Uses of HydrocarbonsNumber of

C atoms State Major Uses

1-4 gas heating and cooking fuel

5-7 liquids, (low boiling)

solvents, gasoline

6-18 liquids gasoline

12-24 liquids jet fuel; camp stove fuel

18-50 liquids, (high boiling)

diesel fuel, lubricants, heating oil

50+ solids petroleum jelly, paraffin wax

1-4 gas heating and cooking fuel

5-7 liquids, (low boiling)

solvents, gasoline

6-18 liquids gasoline

12-24 liquids jet fuel; camp stove fuel

18-50 liquids, (high boiling)

diesel fuel, lubricants, heating oil

50+ solids petroleum jelly, paraffin wax

Name LewisStructure

Formula BoilingPoint

MethaneC H

H

H

HCH4 -162°C

EthaneC

H

H

H C H

H

H

CH3CH3 -89°C

PropaneCH

H

H

C

H

H

C

H

H

HCH3CH2CH3 -42°C

ButaneCH

H

H

C

H

H

C

H

H

C

H

H

HCH3CH2CH2CH3 0°C

PentaneCH

H

H

C

H

H

C

H

H

C

H

H

C

H

H

HCH3CH2CH2CH2CH3 36°C

HexaneCH

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

HCH3CH2CH2CH2CH2CH3 69°C

Alkanes• also know as paraffins• aliphatic, saturated• general formula CnH2n+2 for chains • very unreactive• CH3 groups at ends of chains, CH2 groups in

the middle• chains may be straight or branched

– n-alkane = straight chain

Alkanes - Physical Properties• nonpolar molecules, intermolecular

attractions due to induced dipoles• both boiling points and melting points

generally increase as the size of the molecule increases

• insoluble in water, commonly used as nonpolar solvents

• less dense than water, density increases with size

Structural Isomers• isomers are molecules with the same molecular

formula but different arrangements of the atoms– different chemical and physical properties

• structural isomers are isomers in which the atoms are attached differently– different bonding pattern– structural isomers have different physical properties

• structural isomers may give different products in a reaction, though they undergo same types of reactions

Structural Isomers of C4H10Butane, BP = 0°C Isobutane, BP = -12°C

C C C C

H

H

H H

H H

H H

H

HC

H

H

H

H H

H

C HC

CH H

H

Possible Structural IsomersCarbon Content

Molecular Formula

Possible Isomers

4 C4H10 2 5 C5H12 3 6 C6H14 5 7 C7H16 9 8 C8H18 18 9 C9H20 35

10 C10H22 75

Practice – Draw the 3 structural isomers of pentane

C C C C CH

H H H H H

H

HHHHH

C CH

H H H

HHHH

C HC

H H

H

C

C CH

H H

HH

H

H H

H

C

C

H H

H

C

Example – Draw all 9 structural isomers of heptane

• the prefix hept- means 7, so the molecular formula is C7H16

• Start by drawing the carbon skeleton of the straight chain isomer

C C C C C C C

Example – Draw all 9 structural isomers of heptane

• fill in the hydrogens so each C has 4 bonds

C C C C C C CH

H

H

H

H

H

H

H

H

H

H

H

H H

H

H

C C C C CC

C

H

H H H

HH H

H

H H H H

H

HHH

C C C C HC

C

H H H

HH H

H

H H H

HHH

H

H

C

C C CH

H

H

H

H

H

H

H

H

C

CH3

C H

CH3

C CH

H

H

H H

H

H

HCH3

C HC

H

C

CH3

C C CH

H

H

H

H

H

CH3

H

HCH3

C HC

HC C

H

H

H

H

H

H

C

CH3

CH3

C HC

H

H

H

C CH

H

H

H

CH3

H

H

C

CH3

CH3

C H C CC

CH2CH3

H H H

H H H

HH

H

H

C C H

Alkenes• also known as olefins• aliphatic, unsaturated

– C=C double bonds• formula for one double bond = CnH2n

– subtract 2 H from alkane for each double bond• trigonal shape around C

– flat• much more reactive than alkanes• polyunsaturated = many double bonds

Alkynes• also known as acetylenes• aliphatic, unsaturated• CºC triple bond• formula for one triple bond = CnH2n-2

– subtract 4 H from alkane for each triple bond• linear shape• more reactive than alkenes

Aromatics• Benzene

– resonance hybrid– does not react like alkenes

• Reactions are generally substitutions for H

CH

CHCH

CH

CH

Br

CH

CHCH

CH

CHCH

+ Br2 + HBrFeBr3

CH

CHHC

HCCH

CH

CH

CHHC

HCC

C

H

H

Functional Groups• other organic compounds are hydrocarbons in which

functional groups have been substituted for hydrogens

• a functional group is a group of atoms that show a characteristic influence on the properties of the molecule– generally, the reactions that a compound will perform are

determined by what functional groups it has– since the kind of hydrocarbon chain is irrelevant to the

reactions, it may be indicated by the general symbol RCH3—OH

R group functional group

Functional Groups

Alcohols• R-OH• ethanol = CH3CH2OH

– grain alcohol = fermentation of sugars– alcoholic beverages

• proof number = 2X percentage of alcohol– gasohol

• isopropyl alcohol = (CH3)2CHOH– 2-propanol– rubbing alcohol– poisonous

• methanol = CH3OH– wood alcohol = thermolysis of wood– paint solvent– poisonous

Ethers• R– O – R• ether = diethyl ether = CH3CH2OCH2CH3

– anesthetic• to name ethers, name each alkyl group

attached to the O, then add the word ether to the end

diethyl ether

Aldehydes and Ketones• contain the carbonyl group• aldehydes = at least 1 side H• ketones = both sides R groups• many aldehydes and ketones have

pleasant tastes and aromas• some are pheromones• formaldehyde = H2C=O

– pungent gas– formalin = a preservative– wood smoke, carcinogenic

• acetone = CH3C(=O)CH3

– nail-polish remover

O

C

formaldehyde

acetone

Aldehyde Odors and Flavors• butanal = butter

• vanillin = vanilla

• benzaldehyde = almonds

• cinnamaldehyde = cinnamon

O

HC CH2CH2CH3

O

CH

HC

O

C C

H

H

H

OO

HO

HO

Ketone Odors and Flavors• acetophenone = pistachio

• carvone = spearmint

• ionone = raspberries

• muscone = musk

O

CH3C

O CH3

O

H3C

C

CH3

CH2

CH3

CH3H3C O

C CH3CCH

H

Carboxylic Acids• RCOOH• sour tasting• weak acids• citric acid

– found in citrus fruit • ethanoic acid = acetic acid

– vinegar• methanoic acid = formic acid

– insect bites and stings O

OHCH

O

OHCCH3

OH

O

HO C C

CH2 C

C

O

O

OH

OH

CH2

Esters• R–COO–R• sweet odor• made by reacting carboxylic acid with

an alcoholRaCOOH + RbOH RaCOORb + H2O• name alkyl group from alcohol, then

acid name with ate ending– precedence over carbonyls, but not

carboxylic acid– number from end with ester group

O

COH

C CH3

O

O

aspirin

methyl butanoate

Amines• N containing organic molecules• very bad smelling• form when proteins decompose• organic bases• name alkyl groups attached to the N, then add

the word amine to the end

H3C CH2

NH2

ethylamineH3C CH2

NHH3C

ethylmethylamineH2NCH2CH2CH2CH2CH2NH2

cadaverine

putrescineH2NCH2CH2CH2CH2NH2

Amines• many amines are biologically active

– dopamine – a neurotransmitter– epinephrine – an adrenal hormone– pyridoxine – vitamin B6

• alkaloids are plant products that are alkaline and biologically active– toxic– coniine from hemlock– cocaine from coca leaves– nicotine from tobacco leaves– mescaline from peyote cactus– morphine from opium poppies

HO

HO

CH2CH2NH2

dopamine

N

N

CH3

nicotine

Macromolecules• polymers are very large molecules made by

repeated linking together small molecules – monomers

• natural• modified natural polymers• synthetic

– plastics, elastomers (rubber), fabrics, adhesives• composites

– additives such as graphite, glass, metallic flakes

Natural Polymers• polysaccharides

– cellulose (cotton) – starch

• proteins • nucleic acids (DNA)• natural latex rubber, etc• shellac• amber, lignin, pine rosin• asphalt, tar

Nylon• polyamides• good physical properties

– effected by moisture• very good heat resistance• excellent chemical resistance• excellent wear resistance• nylon 6,6 made by condensing

1,6–hexandiamine, H2N–(CH2)6–NH2, with hexandioic acid, HOOC–(CH2)4–COOH

(CH2)6 NH C

O

(CH2)4 C

O

HN