Question

n-Butane on monochlorination under photochemical condition gives an optically active compound "P". "P" on further chlorination gives dichloro compounds. The number of dichloro compounds obtained (ignore stereoisomers) is:

• A. 3
• B. 4
• C. 5
• D. 6

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
n-Butane is $CH_3-CH_2-CH_2-CH_3$. Monochlorination at C2 gives 2-chlorobutane ($CH_3-CHCl-CH_2-CH_3$), which is chiral (Compound "P").
Step 2: Key Formula or Approach:
Identify all possible positions for a second chlorine atom on 2-chlorobutane.
Step 3: Detailed Explanation:
Structure of P: $C^1H_3-C^2HCl-C^3H_2-C^4H_3$ 1. 1,2-dichlorobutane: Substitution at C1. 2. 2,2-dichlorobutane: Substitution at C2. 3. 2,3-dichlorobutane: Substitution at C3. 4. 1,3-dichlorobutane: (Note: 2-chlorobutane is symmetric in a way that C1/C4 and C2/C3 are relative, but once one Cl is fixed at C2, the positions become distinct). 5. 2,4-dichlorobutane (same as 1,3-dichlorobutane). The unique structural isomers are: 1,2-dichloro, 2,2-dichloro, 2,3-dichloro, and 1,3-dichloro.
Step 4: Final Answer:
There are 4 dichloro compounds obtained.