Chapter 13.0 HYDROCARBONS

are compounds which

contain only carbon and

hydrogen atoms.

13.1 : ALKANES

Hydrocarbon

ALKANES(saturated)

contain only single bond

ALKENES(unsaturated)

contain C=C

CYCLO-ALKANES (saturated)Alkanes which C atoms are

join in rings

ALKYNES(unsaturated)

containC≡C

CYCLO-ALKENES(unsaturated)

HIDROCARBONS

AROMATIC(contain one or more benzene ring)

ALIPHATIC

• Saturated hydrocarbons

- compound with C-C - Example : alkanes and cycloalkanes

– Contain the maximum number of hydrogen atoms that the carbon compound can possess.

• Unsaturated hydrocarbons

-compounds with multiple bonds -Example : alkenes, cycloalkenes, alkynes and aromatic hydrocarbons

– They posses fewer than the maximum number of hydrogen atoms.

ALKANES

Alkanes are known as saturated hydrocarbon which contain only single covalent bonds.

General formula for straight chain of alkanes is CnH2n+2

where n ≥ 1

General formula for cycloalkanes is CnH2n

where n ≥ 3

Each carbon atom in alkanes is

- sp3 hybridised

- tetrahedral with four sigma bond (formed by the four sp3 hybrid orbitals.)

- all bond angles are close to 109.5o

Alkanes IUPAC names have the –ane suffix.

The First Ten Unbranched Alkanes Molecular formula

Structural formula No .of C atoms

Name

CH4 CH4 1 Methane

C2H6 CH3—CH3 2 Ethane

C3H8 CH3—CH2—CH3 3 Propane

C4H10 CH3—(CH2)2—CH3 4 Butane

C5H12 CH3—(CH2)3—CH3 5 Pentane

C6H14 CH3—(CH2)4—CH3 6 Hexane

C7H16 CH3—(CH2)5—CH3 7 Heptane

C8H18 CH3—(CH2)6—CH3 8 Octane

C9H20 CH3—(CH2)7—CH3 9 Nonane

C10H22 CH3—(CH2)8—CH3 10 Decane

• Starting from C4H10 onwards, the alkanes show the phenomenon of chain isomerism.

• They can exist as linear or branched alkanes.

Example

C4H10

CH3(CH2)2CH3 CH3CH(CH3)2

2-

isobutane

C5H12

IUPAC NOMENCLATURE IUPAC NOMENCLATURE

IUPAC – International Union of Pure and Applied Chemistry

Branched - chain alkanes are named according to the following rules:

Choose the longest continuous chain of carbon atoms; this chain determines the parent name for alkanes.

Examples:

CH3CH2CH2CH2CHCH3

| CH3

Parent name: hexane

CH3CH2CH2CH2CHCH3

CH2

CH3

Parent name : heptane

Number the longest chain beginning Number the longest chain beginning with the with the end of the chain nearer the end of the chain nearer the substituent.substituent.

CH3CH2CH2CH2CHCH3

Example:

CH3 substituent

16 4 235

CH3CH2CH2CH2CH

| CH2

| CH3

substituentCH3

1

2

34567

Use rule number 2 to locate the position of the substituent.

The position and the name of the substituent must be written in front of the parent chain.

CH3CH2CH2CH2CHCH3

Examples:

CH3

2-methylhexane

16 4 235

Substituent

-methyl at C-2

CH3CH2CH2CH2CH CH3

| CH2

| CH3

3-methylheptane

1

2

34567

Substituent

-methyl at C-3

butylbutyl

isopropylisopropyl

propylpropyl

ethylethyl

methylmethyl

substituentname

CH3

CH2CH3

CH2CH2CH3

CHCH3

CH3

CH2CH2CH2CH3

Some Common Substituent GroupsSome Common Substituent Groups

Alkane

methane

propane

butane

ethane

isobutyl

sec-butyl

tert-butyl

neopentyl

CH2CHCH3

CH3

CHCH2CH3

CH3

CH3

CH3

CCH3

CH3

CH2CCH3

CH3

cyclopropyl

cyclobutyl

phenyl

benzyl

C6H5 or

CH2

name substituent

BromoBromo -Br-Br

Chloro Chloro -Cl-Cl

Flouro Flouro -F-F

Iodo Iodo -I-I

HydroxylHydroxyl -OH-OH

AminoAmino -NH-NH22

Cyano Cyano -CN-CN

Nitro Nitro -NO-NO22

If If two or more substituents are presenttwo or more substituents are present, , give each substituent a number give each substituent a number corresponding to its location on the longest corresponding to its location on the longest chain.chain.

the substituent should be listed the substituent should be listed alphabeticallyalphabetically. .

In alphabetizing, the prefixes In alphabetizing, the prefixes di, tri, tetra, di, tri, tetra, sec-, tert- are ignoredsec-, tert- are ignored except except iso and iso and neoneo..

Example: 1 2 3 4 5 6

CH3CHCH2CHCH2CH3

| | CH3 CH2

| CH3

4-ethyl-2-methylhexane

If If two substituentstwo substituents are present on the are present on the same carbon atom, same carbon atom, use that number twice use that number twice

Example: CH3

|3 4 5 6

CH3CH2CCH2CH2CH3

| 2 CH2

| 1 CH3

3-ethyl-3-methylhexane

If If two or more identical substituents two or more identical substituents are are present, use present, use prefixes di-(2 identical prefixes di-(2 identical substituents),tri-(3 identical substituents), substituents),tri-(3 identical substituents), tetra-(4 identical substituents).tetra-(4 identical substituents).

CommaCommas are used to separate numbers s are used to separate numbers from each other.from each other.

Example:Example:

CHCH33CHCH――CH CHCH CH33

| || |

CHCH3 3 CHCH33

2,3-dimethylbutane2,3-dimethylbutane

If there are two chains of equal length as If there are two chains of equal length as the parent chain, choose the the parent chain, choose the chain with chain with the greater number of substituents.the greater number of substituents.

7 6 5 4 3 2 1

2,3,5-trimethyl-4-propylheptane (four substituents)

CH3CH2-CH CH CH CHCH3

| | | | CH3 CH2 CH3 CH3

| CH2

| CH3

4 3 2 1

5

6

7

4-sec-butyl-2,3-dimethylheptane (three substituents)

If branching occurs at an equal distance from If branching occurs at an equal distance from either end of the longest chain, choose the either end of the longest chain, choose the name that gives the name that gives the lower number at the first lower number at the first point of difference.point of difference.

6 5 4 3 2 1

CH3CHCH2CH CHCH3

| | | CH3 CH3 CH3

2,3,5-trimethylhexane

(NOT 2,4,5-trimethylhexane)

1 2 3 4 5 6

CYCLOALKANESCYCLOALKANESCycloalkanes – alkanes which carbon Cycloalkanes – alkanes which carbon atoms are joined in atoms are joined in ringsrings..

Cycloalkanes are known as saturated Cycloalkanes are known as saturated hydrocarbon, because it has the hydrocarbon, because it has the maximum number of bonded hydrogen maximum number of bonded hydrogen ( only has single bonds).( only has single bonds).

General formula: General formula:

CCnnHH2n2n where where n = 3, 4, 5, …… n = 3, 4, 5, ……

NOMENCLATURE OF NOMENCLATURE OF CYCLOALKANESCYCLOALKANES

Cycloalkanes Cycloalkanes with only one ringwith only one ring are are named withnamed with the prefix cyclo- to the the prefix cyclo- to the names of the alkanesnames of the alkanes (contain the (contain the same number of carbon atoms)same number of carbon atoms)

Examples: Monocyclic compounds

C3H6 cyclopropane

C4H8 cyclobutane

C5H10 cyclopentane

If only one substituent is present, it is If only one substituent is present, it is not necessary to designate its positionnot necessary to designate its position..

Examples:Examples:

CH3

Chlorocyclopropane

Methylcyclohexane

Cl

If two substituents are present, If two substituents are present, number carbon in the ring number carbon in the ring beginning with the substituent beginning with the substituent according to the according to the alphabetical orderalphabetical order

and and number in the direction that gives number in the direction that gives the next substituent the next substituent the lowest the lowest numbernumber possible. possible.

Examples:

1-ethyl-2-methylcyclohexaneNOT

1-ethyl-6-methylcyclohexane

CH3

CH2CH31

23

4

5 6

1,3-dichlorocyclopentane(NOT 1,5-

dichlorocyclopentane)

Cl Cl1

2

3

4 5

When three or more substituents are present, begin at the carbon with substituent that leads to the lowest set of locants.

Example:CH2CH3

1-chloro-3-ethyl-4-methylcyclohexane

4- chloro-2-ethyl-1-methylcyclohexane

Cl CH3

Locants

chloro

ethyl

methyl

1

3

4 1

2

4

1

2 3

4

56

1

23

4

5 6

1-ethyl-1,3-dimethylcyclopentane(NOT 3-ethyl-1,3-dimethylcyclopentane)

H3C CH2CH3

CH3

When a single ring system is attached to a single chain with a greater number of carbon atoms

or when more than one ring system is attached to a single chain, then it is appropriate to name the compounds as cycloalkylalkane.

Number of C at ring

Number of C at linear chain

1,3-dicyclohexylpropane

1

2

3

Examples:

CH2CH2CH2CH2CH3

1-cyclobutylpentane