Question

Which of the following is correct stability order of alkenes?

• A. Trans-2-butene $>$ Cis-2-Butene $>$ Isobutene $>$ but-1-ene
• B. Cis-2-Butene $>$ Trans-2-butene $>$ Isobutene $>$ but-1-ene
• C. Isobutene $>$ but-1-ene $>$ Cis-2-Butene $>$ Trans-2-butene
• D. Isobutene $>$ Trans-2-butene $>$ Cis-2-Butene $>$ but-1-ene

Hint:

In alkene stability questions, always rank based on: (1) degree of substitution, (2) trans $>$ cis (due to less steric hindrance), and (3) hyperconjugation effects.

Answer 1

The Correct Option is D

The stability of alkenes is influenced primarily by:
Hyperconjugation
Alkyl substitution (more substituted alkenes are more stable)
Steric hindrance (cis isomers are usually less stable than trans) Let’s analyze each alkene: 1. Isobutene (2-methylpropene): A highly substituted (trisubstituted) alkene. It benefits from both +I effect and extensive hyperconjugation.
⇒ Highest stability 2. Trans-2-butene: Disubstituted alkene with groups on opposite sides — less steric hindrance than cis. More stable than cis-2-butene. 3. Cis-2-butene: Also disubstituted but with steric repulsion due to same-side substituents. Less stable than trans. 4. But-1-ene: Monosubstituted alkene, minimal hyperconjugation and substitution.
⇒ Least stable among the given Correct Stability Order: \[ \text{Isobutene} > \text{Trans-2-butene} > \text{Cis-2-butene} > \text{But-1-ene} \]