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JEE Main levelSingle correct optionDifficulty 2 of 3g1123

Which of the following alkenes has the lowest heat of hydrogenation (all give the corresponding alkane)?

  1. A (ethene)
  2. B (propene)
  3. C (2,3-dimethylbut-2-ene)
  4. D (but-2-ene)

Answer: C

A more stable alkene releases less heat on hydrogenation. Alpha hydrogens (hyperconjugation) are 12, 6, 3 and 0 for the four alkenes respectively. The tetrasubstituted alkene is the most stabilised, so it has the lowest heat of hydrogenation.
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