One of the two chair structures of cis-1-chloro-3-methylcyclohexane is more stable than the other by 15.5kj/mol (3.7kcal/mol) . Which is it?

To determine which chair structure of cis-1-chloro-3-methylcyclohexane is more stable, we need to consider the factors that contribute to stability in cyclohexane chair conformations.

One of the main factors that affects stability is the steric strain caused by the interaction between substituents on adjacent carbons. In this case, we have a chlorine (Cl) and a methyl (CH3) group as substituents.

The chlorine atom is larger than the methyl group, so it will experience more steric strain when it is in an axial position (pointing up or down from the ring). On the other hand, the methyl group is smaller and will experience less steric strain in an axial position.

To minimize steric strain, we want to place the larger chlorine atom in an equatorial position (pointing outward from the ring) and the smaller methyl group in an axial position.

Now, let's consider the two possible chair structures of cis-1-chloro-3-methylcyclohexane:

1. In one chair structure, the chlorine atom is in an axial position, and the methyl group is in an equatorial position.
2. In the other chair structure, the chlorine atom is in an equatorial position, and the methyl group is in an axial position.

Since the chlorine atom experiences more steric strain in an axial position, the chair structure with the chlorine atom in an equatorial position will be more stable.

Therefore, the chair structure of cis-1-chloro-3-methylcyclohexane with the chlorine atom in an equatorial position is more stable than the other by 15.5 kJ/mol (3.7 kcal/mol).