Question

Find stability order of the following alkenes:
(a) Cis-but-2-ene
(b) 2,3-Dimethylbut-2-ene
(c) 2-Methylbut-2-ene
(d) Propene

• A. b > a > d > c
• B. b > c > a > d
• C. a > c > b > d
• D. b > a > c > d

Hint:

The stability of alkenes increases as the number of alkyl substituents on the double-bonded carbons increases. This is due to the effects of hyperconjugation and inductive effects.

Answer 1

The Correct Option is B

The stability of alkenes is influenced by several factors, including the degree of substitution, the presence of electron-donating groups, and steric strain. Generally, more substituted alkenes are more stable due to hyperconjugation and the inductive effect. Let's analyze the given alkenes:

1. Cis-but-2-ene: This is a disubstituted alkene with two substituents on the double bond but has some steric strain due to the cis configuration.
2. 2,3-Dimethylbut-2-ene: This is a tetrasubstituted alkene as both the carbons in the double bond are connected to two additional carbon groups each. It is highly stable due to extensive hyperconjugation and lack of steric hindrance.
3. 2-Methylbut-2-ene: This is a trisubstituted alkene, which is more stable than disubstituted alkenes due to increased hyperconjugation but lacks the stability of a tetrasubstituted alkene.
4. Propene: This is a monosubstituted alkene and generally the least stable among the choices due to having only one substituent on the double bond.

Based on the degree of substitution:

• 2,3-Dimethylbut-2-ene (tetrasubstituted) is the most stable.
• 2-Methylbut-2-ene (trisubstituted) is the second most stable.
• Cis-but-2-ene (disubstituted) is less stable due to steric strain.
• Propene (monosubstituted) is the least stable.

Therefore, the stability order of the alkenes is: b > c > a > d.