ReviewAlkanesCnH2n+2

C4H10 a) ethaneb) propanec) butaned) pentane CH3 (CH2) CH3

butane

2

Newman projections

butane

staggered eclipsedstable

1

1

2

2

3

3

4

4

Nomenclature

1 3 4 5 6 7

heptane

12

21

334 4

5

5

6

6

7

7

heptane heptane

branches branches branches

2

3 2 4

Nomenclature2

1

3 4 5 6 7

2-3-4-

5-

methylethyl

propylethyl

3,5-diethyl

ethylpropyl

methyl

3,5-diethyl-2-methyl -4-propylheptane

Cycloalkaneslinear alkanes

branched alkanes

cycloalkanes closed rings CnH2n

bond angle = 60o tetrahedral angle = 109o

very unstable

propane

CnH2n+2

1

23cyclo

Cycloalkanes

cyclobutane

bond angle = 88o

tetrahedral angle = 109o

unstable

Cycloalkanes

cyclopentane

bond angle = 108o

tetrahedral angle = 109o

stable

Cycloalkanes

1,3-dichlorocyclobutane cis- trans-1,3-dichlorocyclobutane

geometric isomers

-

-

Cycloalkanes

cyclohexane

predicted bond angle = 120o

tetrahedral angle = 109o

stable

cyclohexane

chair conformation boat conformationstable unstable

axial positionsequatorial positions

crowded only Hlarger groups

cyclohexane

cis- cis-1,2-dimethylcyclohexane

trans- trans-1,2-dimethylcyclohexane

axial-equatorial

equatorial-equatorial axial-axial

1,2-dimethylcyclohexane

1,2-dimethylcyclohexane

Optical isomerism

bromo

**

bromo trans-

*

*

chloroiodomethane hexane

cyclopentane 1,3-dibromocyclopentaneno C*

C* =Stereocenter4 different substituents

3-methyl

Alkane Summary1. Alkanes - sp3 hybridized

2. Relatively unreactive Substitution with halogens

Combustion

3. Non-polar IMF = London Dispersion Forces

sizestructure

4. Free rotation around C-C bondsconformations

5. Non-cyclic alkanes - structural isomers

6. Cyclic alkanes - geometric isomerscis-, trans-

7. Alkanes - optical isomersstereocenters C*