Question

What structural feature of cycloalkanes makes cis, trans isomerism in them possible?

Short answer

Answer: The restricted rotation around carbon-carbon single bonds (C-C) due to their cyclic structure allows for cis, trans isomerism in cycloalkanes. This leads to a fixed spatial arrangement of substituent groups, resulting in distinct isomers.

Step-by-step solution

Understand the Structure of Cycloalkanes

Cycloalkanes are hydrocarbons that consist of carbon and hydrogen atoms arranged in a ring structure. They typically have the general formula CnH2n. Examples of cycloalkanes include cyclopropane (C3H6), cyclobutane (C4H8), cyclopentane (C5H10), and cyclohexane (C6H12).

Define Isomerism and Cis, Trans Isomerism

Isomerism refers to the existence of two or more distinct compounds with the same molecular formula but different structures or arrangements of atoms. In cis, trans isomerism (geometric isomerism), two isomers differ in the orientation of substituents around a double bond or ring structure.

Examine the Structural Feature that Allows Cis, Trans Isomerism in Cycloalkanes

The structural feature that makes cis, trans isomerism possible in cycloalkanes is the restricted rotation around carbon-carbon single bonds (C-C) due to their cyclic structure. This restricted rotation in a ring prevents the free rotation of substituent groups as it would be in open-chain alkanes and leads to a fixed spatial arrangement of these substituents. Thus, different spatial arrangements are considered as distinct isomers.

Explain the Occurrence of Cis, Trans Isomerism with an Example

To better understand cis, trans isomerism in cycloalkanes, let's consider the example of 1,2-dimethylcyclohexane. Both carbons of the cyclohexane ring have a methyl group (CH3) attached to them. Due to the restricted rotation around the carbon-carbon single bonds, two distinct isomers can be formed depending on the position of the methyl groups: 1. Cis-1,2-dimethylcyclohexane: Both methyl groups are on the same side of the ring (either both on the top or both on the bottom). 2. Trans-1,2-dimethylcyclohexane: One methyl group is on the top, and the other one is on the bottom side of the ring. These distinct spatial arrangements of the methyl groups result in the existence of cis and trans isomers for 1,2-dimethylcyclohexane. In conclusion, the restricted rotation around single carbon-carbon bonds in cycloalkanes leads to their fixed spatial arrangement of substituent groups, enabling the possibility of cis, trans isomerism in these compounds.