Question

How many products (including stereoisomers) are expected from monochlorination of the following compound?
$CH_3-CH-CH_2-CH_3$

• A. 3
• B. 6
• C. 5
• D. 2

Hint:

When monochlorinating a compound with asymmetric carbons (especially secondary carbons), be sure to account for stereoisomers.

Answer 1

The Correct Option is A

Monochlorination involves replacing one hydrogen atom with a chlorine atom. We need to consider all possible positions where chlorine can substitute a hydrogen and whether any of these substitutions create a stereocenter.

1. Chlorination at C1: CH₂Cl-CH₂-CH₂-CH₃. This is 1-chlorobutane.

2. Chlorination at C2: CH₃-CHCl-CH₂-CH₃. This is 2-chlorobutane. Since C2 becomes a chiral center, there are two stereoisomers (enantiomers): (R)-2-chlorobutane and (S)-2-chlorobutane.

3. Chlorination at C3: CH₃-CH₂-CHCl-CH₃. This is also 2-chlorobutane (same as chlorination at C2 when considering connectivity). The molecule now has a chiral center, again producing two stereoisomers: (R)-2-chlorobutane and (S)-2-chlorobutane.

4. Chlorination at C4: CH₃-CH₂-CH₂-CH₂Cl. This is 1-chlorobutane, identical to the product from C1 chlorination.

Therefore, there are three distinct monochlorinated products: 1-chlorobutane, (R)-2-chlorobutane, and (S)-2-chlorobutane. The number of products including stereoisomers is 3.