Which effect explains the stability of ${\text{(CH}}_3{)}_2\text{C}={\text{C(CH}}_3{)}_2$ compared to ${\text{CH}}_3{\text{CH}}_2\text{CH}={\text{CH}}_2$?

Solution

1. Count the number of alpha-hydrogens available for hyperconjugation in each alkene.
2. 2,3-dimethylbut-2-ene has 12 alpha-hydrogens.
3. But-1-ene has only 2 alpha-hydrogens.
4. Greater number of alpha-hydrogens leads to more hyperconjugative structures and higher stability.
5. Hence the answer is (B).