What happens when an aldehyde is treated with lithium aluminium hydride ?

Options

A. Primary alcohol is formed
B. Secondary alcohol is formed
C. Tertiary alcohol is formed
D. No reaction

Answer

To answer the question about what happens when an aldehyde is treated with lithium aluminium hydride (LiAlH4), we can break down the reaction step by step.

### Step 1: Understanding the Reactants
- Aldehydes have the general formula RCHO, where R is an alkyl or aryl group and CHO is the carbonyl functional group.
- Lithium aluminium hydride (LiAlH4) is a strong reducing agent commonly used in organic chemistry to reduce carbonyl compounds.

### Step 2: Reaction Mechanism
1. **Nucleophilic Attack**: The hydride ion (H-) from LiAlH4 acts as a nucleophile and attacks the carbon atom of the carbonyl group (C=O) in the aldehyde. This carbon is electrophilic due to the partial positive charge created by the oxygen.

2. **Formation of Alkoxide Intermediate**: After the nucleophilic attack, the carbonyl group is converted into an alkoxide intermediate. This intermediate has a negatively charged oxygen atom (RCH(OH)−).

3. **Protonation**: The alkoxide can then be protonated by water or another proton source, leading to the formation of the corresponding alcohol.

### Step 3: Final Product
- The final product of the reaction is a primary alcohol. For example, if we start with an aldehyde like ethanal (acetaldehyde, CH3CHO), the product after reduction will be ethanol (CH3CH2OH).

### Summary of the Reaction
- Aldehyde (RCHO) + LiAlH4 → Primary Alcohol (RCH2OH)

### Final Answer
When an aldehyde is treated with lithium aluminium hydride, it is reduced to a primary alcohol.

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