Question

Which is more stable, a 1, 4-trans disubstituted cyclohexane or its cis isomer?

Short answer

1, 4-trans disubstituted cyclohexane is more stable than its cis isomer because 1, 4-cis disubstituted cyclohexane shows 1, 3 diaxial interaction.

Step-by-step solution

Chair form of cyclohexane

There are four conformations possible for cyclohexane such as a chair, twist boat, boat, half chair. Among all the four conformations chair form of cyclohexane is considered a very stable one. Chair conformation of cyclohexane is as follows;

We simply can say if the relation is up-up then cis, if down–down relationship then trans.

If the up-down or down-up relation between the bond then trans.

1, 4-trans disubstituted cyclohexane

The structure of 1, 4-trans disubstituted cyclohexane is as follows;

In 1, 4-trans disubstituted cyclohexane one group lies in upward while the other is downward. In 1, 4-trans disubstituted cyclohexane form if we observe it is seen that both the groups lie in an equatorial position. Hence 1, 4-trans disubstituted cyclohexane is more stable.

1, 4-cis disubstituted cyclohexane

The structure of 1, 4-cis disubstituted cyclohexane is as follows;

In 1, 4-cis disubstituted cyclohexane both the group lie either up or down. If we observe the structure then it is seen that in the 1, 4-cis disubstituted cyclohexane one group lies in axial while the other group lies in an equatorial position. The group which lies in axial position shows 1, 3 diaxial repulsions. Hence it is less stable.