In which reaction racemic mixture is obtained as product ?

Options

A. `Ph-CHO+HCNto`
B. `H_(3)C-underset(C_(2)H_(5))(CH)-CH_(2)-OH+SOCl_(2)overset("pyridine")(to)`
C. `H_(3)C-underset(Cl)underset(|)(CH)-CH_(2)-CH_(3)+C_(3)H_(7)overset(ө)(O)overset(o+)(Na)underset(Delta)overset(ROH)(to)`
D. All of these

Answer

To determine in which reaction a racemic mixture is obtained, we need to analyze the given reactions and identify the one that produces both enantiomers in equal amounts. Here’s a step-by-step solution:

### Step 1: Understand Racemic Mixture
A racemic mixture is defined as a mixture that contains equal amounts of two enantiomers, which are non-superimposable mirror images of each other. Such mixtures are optically inactive because the optical activities of the two enantiomers cancel each other out.

**Hint:** Remember that for a racemic mixture to form, a chiral center must be created during the reaction.

### Step 2: Analyze the First Reaction
In the first reaction, benzaldehyde (C6H5CHO) reacts with hydrogen cyanide (HCN). The nucleophile (CN-) can attack the electrophilic carbon of the carbonyl group from either above or below the plane, leading to the formation of two different products (enantiomers).

**Hint:** Look for reactions involving carbonyl compounds where nucleophilic addition can lead to chiral centers.

### Step 3: Analyze the Second Reaction
The second reaction involves the conversion of an alcohol (CH3CH(CH2)2OH) to an alkyl chloride using thionyl chloride (SOCl2) in the presence of pyridine. Since the carbon that bears the OH group is not chiral, the product will not be a racemic mixture.

**Hint:** Identify if there is a chiral center in the reactants; if not, a racemic mixture cannot form.

### Step 4: Analyze the Third Reaction
In the third reaction, CH3Cl reacts with a strong nucleophile (C3H7O-) in an SN2 mechanism. The nucleophile attacks from the opposite side of the leaving group, leading to inversion of configuration but not the formation of a racemic mixture, as there is no chiral center created.

**Hint:** Remember that SN2 reactions lead to inversion of configuration and do not produce racemic mixtures.

### Step 5: Analyze the Fourth Option
The fourth option states "all of these," which implies that all previous reactions yield racemic mixtures. However, we have established that only the first reaction produces a racemic mixture.

**Hint:** Be cautious with options that claim all reactions yield the same result; verify each one individually.

### Conclusion
After analyzing all the reactions, we conclude that the first reaction is the only one that produces a racemic mixture. Therefore, the correct answer is:

**Final Answer:** Option 1 (the reaction between benzaldehyde and hydrogen cyanide produces a racemic mixture).