Structural Isomers

C - C - C - C - C - C - C - C

CC

C - C - C - C - C - C - C

C

C

C

Structural isomers:Compounds with same molecular formula but different structural formula.

Isomers differ in their properties such as boiling point and melting point.

More branched the structure, lower its boiling point - Closer compounds stack, stronger the IMFs.

branched unbranched

butane 2-methylpropane

C4H10isomers

More carbon atoms - more structural isomers.

Octane - 18 different structural isomersDecane - 75Eicosane - 366 319(20 carbon alkane)

3-methyl-5-ethylheptane decane

C - C - C - C - C - C - C

C

C

CC - C - C - C - C

CC

C C

C

Draw and name 2 structural isomers of pentane.

C - C

C

C - C - C - C

C

C -

C2-methylbutane

2,2-dimethylpropane C - C

C

C - C -

C - C

C

C - C - pentane2-methylbutane

Take care when naming your isomers to be sure you don’t have the same thing.

3-ethyl-2-methylhexane is a structural isomer of which straight chained alkane?

6 carbons + 2 carbons + 1 carbon = 9 carbons

The alkane with 9 carbons is nonane.

hexane ethyl methyl

C - C - C - C

C

C

C - C - 1 2 3 4 5 6

C

CYCLOALKANES

• Same naming rules – but add prefix“cyclo” • Name the carbon ring first, then number the carbons so

as to give the alkyl groups the lowest set of numbers.

1,2-dimethylcyclopentane

1-methylcyclobutane

C

CC

C

C

C

CC

C

C

C

C

CC

CC

C

C

cyclohexane