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Question: Which is most stable alkene ?...

Which is most stable alkene ?

A

CH2=CH2CH_2 = CH_2

B

CH3−CH=CH2CH_3 - CH = CH_2

C

CH3−CH=CH−CH3CH_3 - CH = CH - CH_3

D

CH3CH3CH3−C=C−CH3\qquad CH_3 \quad CH_3 \\ CH_3-C=C-CH_3

Answer

CH3−C(CH3)=C(CH3)−CH3CH_3-C(CH_3)=C(CH_3)-CH_3

Explanation

Solution

The stability of alkenes increases with the number of alkyl substituents attached to the double bond carbons. This is due to the electron-donating nature of alkyl groups, which stabilize the pi electron system through inductive effect and hyperconjugation.

  • CH2=CH2CH_2 = CH_2 (Ethene) is unsubstituted (0 alkyl groups).
  • CH3−CH=CH2CH_3 - CH = CH_2 (Propene) is monosubstituted (1 alkyl group).
  • CH3−CH=CH−CH3CH_3 - CH = CH - CH_3 (But-2-ene) is disubstituted (2 alkyl groups).
  • CH3−C(CH3)=C(CH3)−CH3CH_3-C(CH_3)=C(CH_3)-CH_3 (2,3-Dimethylbut-2-ene) is tetrasubstituted (4 alkyl groups). The tetrasubstituted alkene (CH3−C(CH3)=C(CH3)−CH3CH_3-C(CH_3)=C(CH_3)-CH_3) has the highest degree of substitution and is therefore the most stable.