Question

Write the major alkene that would be formed by dehydrohalogenation of 2-Bromopentane.

Hint:

In reasoning questions, always consider electronic effects (inductive, resonance), medium conditions (acid/base), and steric effects for explanations.

Answer 1

Step 1: Dehydrohalogenation is an elimination reaction in which a hydrogen atom and a halogen atom are removed from adjacent carbon atoms, leading to the formation of an alkene.
Step 2: The structure of 2-bromopentane is: \[ \text{CH}_3 - \text{CHBr} - \text{CH}_2 - \text{CH}_2 - \text{CH}_3 \] Step 3: In the presence of alcoholic KOH (a strong base), elimination follows Zaitsev’s Rule, which favors the formation of the **more substituted alkene.
Step 4: Removal of a $\beta$-hydrogen from the third carbon (next to the carbon bearing bromine) leads to the formation of 2-pentene, which is more stable and thus the major product.
Conclusion: The major alkene obtained from dehydrohalogenation of 2-bromopentane is 2-pentene.