Question

5 multiple choice 2 points which has the greatest molar heat of combustion? trans - 1,3 - dimethylcyclopentane cycloheptane cis - 1,2 - dimethylcyclopentane trans - 1,2 - dimethylcyclopentane methylcyclohexane

Explanation:

Step1: Consider ring - strain and number of carbon atoms

The molar heat of combustion is related to the stability of the molecule. Molecules with higher ring - strain and more carbon atoms generally have a higher molar heat of combustion. Cycloheptane has a larger ring compared to cyclopentanes and methylcyclohexane. Larger rings can have more ring - strain in some cases. Also, more carbon atoms mean more bonds to break and form during combustion.

Step2: Analyze each option

Trans - 1,3 - dimethylcyclopentane, cis - 1,2 - dimethylcyclopentane, and trans - 1,2 - dimethylcyclopentane are cyclopentane derivatives. Methylcyclohexane is a cyclohexane derivative. Cycloheptane has 7 carbon atoms while the cyclopentane derivatives have 7 carbon atoms in total (5 in the ring and 2 in the methyl groups) and methylcyclohexane has 7 carbon atoms. But cycloheptane has a less stable ring structure due to ring - strain compared to cyclohexane and cyclopentane derivatives with proper substitution patterns that can relieve strain.

Answer:

cycloheptane