Question

One of the chair conformers of cis-1,3-dimethylcyclohexane is 5.4 kcal/mol less stable than the other. How much steric strain does a 1,3-diaxial interaction between two methyl groups introduce into the conformer

Answer 1

The 1,3-diaxial interaction between two methyl groups in the cis-1,3-dimethylcyclohexane chair conformer introduces 5.4 kcal/mol of steric strain, making it less stable compared to the conformer where both methyl groups are in equatorial positions.

Step-by-step explanation:

The student is asking about the difference in stability between two chair conformers of cis-1,3-dimethylcyclohexane. Specifically, the student wants to know the amount of steric strain introduced by a 1,3-diaxial interaction between two methyl groups in one of the conformers.

When considering the conformations of substituted cyclohexanes, each cyclohexane chair conformer has different energy levels depending on the orientation of the substituents. In the case of cis-1,3-dimethylcyclohexane, the less stable conformer has the two methyl groups in axial positions, which results in steric repulsion known as 1,3-diaxial interactions. This interaction is a source of steric strain and makes this conformer less stable by 5.4 kcal/mol compared to the more stable conformer with both methyl groups in equatorial positions.

Therefore, the 1,3-diaxial interaction between two methyl groups introduces 5.4 kcal/mol of steric strain into the less stable chair conformer of cis-1,3-dimethylcyclohexane.

Answer 2

See explanation

Step-by-step explanation:

the Cis structure, we can have two possibilities. The methyl groups can go both in axial positions or both in equatorial positions. We have to remember that cis it means "same orientation", so in the axial positions, both methyl groups go up. (Both have the same orientation). In the equatorial positions, both groups go down.

In the axial positions, we will have more steric hindrance because the groups are close to each other. Therefore, we will have more energy and the structure will be less stable. In the equatorial positions, we dont have any steric hindrances, so we will have less energy and more stability.

See figure 1

I hope it helps!