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Which of the following has the smallest heat of hydrogenation per mole ?A. 1-buteneB. Trans-2-buteneC. Cis-2-buteneD. 1, 3 butadiene

Answer» Correct Answer - D
1, 3-butadiene shows smallest heat of hydrogenation due to its higher stability (which is due to resonance)
Trans-2-butene is more stable than cis-2-butene on the basis of heat of hydrogenation.
1-butene is less stable than 2-butene due to hyper conjugation. `CH_(3)-CH=CH-CH_(3)` (Shows six no-bond resonating structures)
While, 1-butene due to hyperconjugation shows two no-bond resonating structures. (Resonance is more powerful than hyperconjugation)
Order of stability
1, 3-butadiene `gt` trans-2-butene `gt` cis-2-butene `gt` 1-butene
Heat of hydrogenation
1-butene `gt` cis-2-butene `gt` trans-2-butene `gt` 1, 3-butadiene


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