Question

Addition of hydrogen bromide to but-2-ene and but-1-ene forms

• A. 1-bromobutane and 2-bromobutane respectively
• B. 1-bromobutane only
• C. 2-bromobutane and 1-bromobutane respectively
• D. 2-bromobutane only

Hint:

In the addition of HBr to alkenes, the more substituted carbon gets the halogen (Markovnikov's rule), leading to the formation of 2-bromobutane.

Answer 1

The Correct Option is D

Step 1: Understanding the reaction mechanism.
The addition of hydrogen bromide (HBr) to alkenes follows Markovnikov's rule. In the case of but-2-ene, the addition of HBr leads to the formation of 2-bromobutane, as the bromine attaches to the carbon with more alkyl groups (which is more substituted). For but-1-ene, 2-bromobutane is also formed.
Step 2: Analyzing the options.
(A) 1-bromobutane and 2-bromobutane respectively: Incorrect. This is not the correct order of products.
(B) 1-bromobutane only: Incorrect. This product is not obtained in either case.
(C) 2-bromobutane and 1-bromobutane respectively: Incorrect. The correct product is 2-bromobutane, not 1-bromobutane.
(D) 2-bromobutane only: Correct — Both but-2-ene and but-1-ene lead to the formation of 2-bromobutane after the addition of HBr.
Step 3: Conclusion.
The correct answer is (D) 2-bromobutane only, as the product of both reactions is 2-bromobutane.