Question

Which of the following diene will have the least heat of hydrogenation?

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

Option A :


It has 6 $\alpha$-hydrogens.

Option B:


It has 6 $\alpha$-hydrogens.

Option C


It has 10 $\alpha$-hydrogens.

Option D:

It has 6 $\alpha$-hydrogens.
Structure (a) has isolated double bonds, so it has the least stability among the other givev dienes which are conjugated.
More the stability, lesser is the heat of hydrogenation.
Since (c) has maximum number of $\alpha$-hydrogens, it is the most stable and has the least heat of hydrogenation.