Answer to Question #129086 in Organic Chemistry for Moreen

Question

c) Explain using structures why trans-2-Butene (a disubstituted alkene) is more stable than cis-2-butene (another disubstituted alkene)?

Answer 1

The stability of an alkene can be determined by measuring the amount of energy associated with the hydrogenation of the molecule. Since the double bond is breaking in this reaction, the energy released in hydrogenation is proportional to the energy in the double bond of the molecule. This is a useful tool because heats of hydrogenation can be measured very accurately. The ΔH

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ΔHo is usually around -30 kcal/mol for alkenes. Stability is simply a measure of energy. Lower energy molecules are more stable than higher energy molecules. More substituted alkenes are more stable than less substituted ones due to hyperconjugation. They have a lower heat of hydrogenation. The following illustrates stability of alkenes with various substituents:

trans is more stable because this is more symmetrical .