Which of the following reaction will not form racemic mixture as product?

Options

A.
B.
C.
D.

Answer

To determine which reaction will not form a racemic mixture, we need to analyze each reaction and identify whether the product contains a chiral center. A racemic mixture is formed when a reaction produces a chiral compound that can exist in two enantiomeric forms.

### Step-by-Step Solution:

1. **Understanding Racemic Mixtures**:
- A racemic mixture consists of equal amounts of two enantiomers (mirror-image isomers). For a compound to be chiral, it must have four different substituents attached to a central carbon atom.

2. **Analyzing Reaction A**:
- The reaction involves a carbonyl compound reacting with HCN to form a cyanohydrin.
- The carbon atom that is formed during this reaction becomes chiral because it has four different groups attached to it (CH3, CH2, CN, and OH).
- **Conclusion**: Reaction A will form a racemic mixture.

3. **Analyzing Reaction B**:
- The reaction involves a compound with two identical methyl groups reacting with HCl.
- The resulting carbocation has two identical groups (the two methyl groups), which means the carbon is not chiral.
- **Conclusion**: Reaction B will not form a racemic mixture.

4. **Analyzing Reaction C**:
- The reaction involves a cyclohexane ring with a double bond and a methyl group reacting with HCl.
- The formation of a tertiary carbocation occurs, which is chiral due to having four different groups attached (methyl, hydrogen, chlorine, and the rest of the cyclohexane).
- **Conclusion**: Reaction C will form a racemic mixture.

5. **Analyzing Reaction D**:
- The reaction involves butene reacting with HBr.
- A secondary carbocation is formed, which can also lead to a chiral center being formed depending on the attack of bromine.
- The resulting product has four different groups attached to the chiral carbon.
- **Conclusion**: Reaction D will form a racemic mixture.

### Final Answer:
The reaction that will not form a racemic mixture is **Reaction B**.