Question

# Arrange the following in the increasing order of their heat of hydrogenation: P<Q<R<SS<R<P<QS<R<Q<PP<Q<S<R

Solution

## The correct option is A P<Q<R<SHeat of hydrogenation∝1stability of alkene The stability of alkenes depends upon two major factors: i) Conjugation ii) Number of α−hygrogens (P) being most stable has least heat of hydrogenation since the double bond is in conjugation. Among (Q), (R) and (S), the number of α−hygrogens are in the order: Q>R>S Hence, the heat of hydrogenation follows the trend: P<Q<R<S

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