Question

Using a planar pentagon representation for the cyclopentane ring, draw structural formulas for the cis and trans isomers of the following. (a) 1,2 -Dimethylcyclopentane (b) 1,3 -Dimethylcyclopentane

Short answer

Question: Draw the structural formulas for cis and trans isomers of 1,2-dimethylcyclopentane and 1,3-dimethylcyclopentane. Answer: For cis-1,2-dimethylcyclopentane, the two methyl groups are on the same side of the cyclopentane ring and attached to carbon-1 and carbon-2. In the trans-isomer, the methyl groups are on opposite sides, still attached to carbon-1 and carbon-2. For cis-1,3-dimethylcyclopentane, the methyl groups are on the same side of the cyclopentane ring, attached to carbon-1 and carbon-3. In the trans-isomer, the methyl groups are on opposite sides, attached to carbon-1 and carbon-3.

Step-by-step solution

Draw the basic cyclopentane ring structure

Draw a regular pentagon, which is a 5-sided polygon with equal side lengths, to represent the cyclopentane ring.

Identify the position of methyl groups in 1,2-dimethylcyclopentane

Methyl groups are attached to carbon-1 and carbon-2 in the 1,2-dimethylcyclopentane. Label one of the vertices of the pentagon as carbon-1, the adjacent vertex as carbon-2, and continue labeling the remaining vertices up to carbon-5.

Draw the cis-isomer for 1,2-dimethylcyclopentane

For cis-1,2-dimethylcyclopentane, the two methyl groups should be on the same side of the cyclopentane ring. Attach a methyl group (CH3) to carbon-1 and carbon-2, directing both towards the same side (either right or left of the ring).

Draw the trans-isomer for 1,2-dimethylcyclopentane

For trans-1,2-dimethylcyclopentane, the two methyl groups should be on opposite sides of the cyclopentane ring. Attach a methyl group (CH3) to carbon-1 and carbon-2, directing them towards opposite sides (one right and one left of the ring).

Identify the position of methyl groups in 1,3-dimethylcyclopentane

Methyl groups are attached to carbon-1 and carbon-3 in 1,3-dimethylcyclopentane. Label one of the vertices of the pentagon as carbon-1, the next adjacent vertex as carbon-2, the next adjacent as carbon-3, and continue labeling the remaining vertices up to carbon-5.

Draw the cis-isomer for 1,3-dimethylcyclopentane

For cis-1,3-dimethylcyclopentane, the two methyl groups should be on the same side of the cyclopentane ring. Attach a methyl group (CH3) to carbon-1 and carbon-3, directing both towards the same side (either right or left of the ring).

Draw the trans-isomer for 1,3-dimethylcyclopentane

For trans-1,3-dimethylcyclopentane, the two methyl groups should be on opposite sides of the cyclopentane ring. Attach a methyl group (CH3) to carbon-1 and carbon-3, directing them towards opposite sides (one right and one left of the ring).