Which of the following can not be made by reduction of ketone or aldenhyde with `NaBH_4` ?

Options

A. 1 - Butanol
B. 2 - Butanol
C. 2 - Methyl - 1 - propanol
D. 2 - Methyl - 2 - propanol

Answer

To solve the question of which alcohol cannot be prepared by the reduction of a ketone or aldehyde with NaBH4, we will analyze each of the given alcohols step by step.

### Step 1: Understand the Reducing Agent
NaBH4 (Sodium Borohydride) is a common reducing agent used to reduce ketones and aldehydes to their corresponding alcohols. It adds hydrogen to the carbonyl carbon and the oxygen atom.

### Step 2: Analyze the Given Alcohols
We have four alcohols to consider. We need to determine if each can be formed by reducing a ketone or aldehyde.

1. **1-Butanol (CH3-CH2-CH2-CH2-OH)**
- This alcohol can be formed by reducing butanal (an aldehyde). The reaction is:
\[ \text{Butanal} \xrightarrow{\text{NaBH}_4} \text{1-Butanol} \]
- Thus, 1-butanol can be prepared from an aldehyde.

2. **2-Butanol (CH3-CH(OH)-CH2-CH3)**
- This alcohol can be formed by reducing butan-2-one (a ketone). The reaction is:
\[ \text{Butan-2-one} \xrightarrow{\text{NaBH}_4} \text{2-Butanol} \]
- Hence, 2-butanol can be prepared from a ketone.

3. **2-Methyl-1-Propanol (CH3-CH(CH3)-CH2-OH)**
- This alcohol can be formed by reducing 2-methylpropanal (an aldehyde). The reaction is:
\[ \text{2-Methylpropanal} \xrightarrow{\text{NaBH}_4} \text{2-Methyl-1-Propanol} \]
- Therefore, 2-methyl-1-propanol can be prepared from an aldehyde.

4. **2-Methyl-2-Propanol (tert-Butanol, (CH3)3COH)**
- This alcohol cannot be prepared by reducing any aldehyde or ketone. The reason is that 2-methyl-2-propanol is a tertiary alcohol, and there is no corresponding ketone or aldehyde that can yield this alcohol through reduction. The structure of 2-methyl-2-propanol does not allow for the addition of hydrogen to a carbonyl carbon in a way that would yield this alcohol.

### Conclusion
The alcohol that cannot be prepared by the reduction of a ketone or aldehyde with NaBH4 is **2-Methyl-2-Propanol**.