`CH_(3)CHO + LiAlH_(4) to CH_(3)CH_(2)OH` Nucleophile added in this reaction is

Options

A. `AlH_(4)^(-)`
B. `Li^(+)`
C. `H_(-)^(+)`
D. `H^(-)`

Answer

To determine the nucleophile added in the reaction between CH₃CHO (acetaldehyde) and LiAlH₄ (lithium aluminium hydride), we can analyze the reaction step by step.

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactants in this reaction are CH₃CHO (acetaldehyde) and LiAlH₄ (lithium aluminium hydride).

2. **Understand the Role of LiAlH₄**: LiAlH₄ is a strong reducing agent. It can donate hydride ions (H⁻) to other compounds, which is essential for the reduction process.

3. **Dissociation of LiAlH₄**: In the presence of a substrate like acetaldehyde, LiAlH₄ can dissociate to form LiAlH₃ and a hydride ion (H⁻). The relevant part of the dissociation is:
\[ \text{LiAlH}_4 \rightarrow \text{LiAlH}_3 + \text{H}^- \]

4. **Nucleophilic Attack**: The hydride ion (H⁻) acts as a nucleophile. It attacks the electrophilic carbon atom of the carbonyl group (C=O) in acetaldehyde. This results in the formation of an alkoxide intermediate:
\[ \text{CH}_3CHO + \text{H}^- \rightarrow \text{CH}_3CH(OH) \text{ (alkoxide)} \]

5. **Protonation of the Alkoxide**: The alkoxide formed then undergoes protonation (addition of H⁺) to yield the final product, ethanol (CH₃CH₂OH):
\[ \text{CH}_3CH(OH) + \text{H}^+ \rightarrow \text{CH}_3CH_2OH \]

6. **Conclusion**: The nucleophile that is added in this reaction is the hydride ion (H⁻) from LiAlH₄.

### Final Answer:
The nucleophile added in this reaction is **H⁻** (hydride ion).