Question

The order of heat of hydrogenation in following compound is:

• A. I < II < IV < III
• B. III < IV < II < I
• C. II < III < I < IV
• D. II < IV < I < III

Answer 1

The correct option is B III < IV < II < I

The heat of hydrogenation is proporitonal to the number of $\alpha -$ hydrogen andstability of alkene. III is more stable as it contains more hyper conjugation and resonance stabilized. Then IV is stable due to resonance and less hyperconjugation than first. In I and II, $\alpha -$ hydrogen is more in II than first, therefore, II is more stable than first. Therefore the order is III < IV < II < I.