Question

Which isomer is more stable, cis-decalin or trans-decalin? Explain.

Short answer

Trans-decalin is more stable as it shows fewer steric interactions.

Step-by-step solution

Cis and trans conformation of decalin

In cis-decalin, the hydrogen atoms at the bridgehead carbons are on the same face of the rings; in trans-decalin, the bridgehead hydrogens are on opposite faces.

Axial and equatorial positions

Axial bonds are the bonds that are perpendicular or vertical to the ring plane. Equatorial bonds are approximately horizontal in the plane of the ring.

Conformation stability

Cis- and trans-decalin, respectively

Trans-decalin is more stable than cis-decalin because the rings are at a maximum distance in trans-decalin, and in cis-decalin show steric interactions and hence, decreases its stability.