Consider the following reaction `CH_3CHO+LiAlH_4 rarr CH_3CH_2OH` Nucleophile added in this reaction is

Options

A. `AlH_4^-`
B. `Li^+`
C. `H^+`
D. `H^-`

Answer

To determine the nucleophile in the reaction `CH3CHO + LiAlH4 → CH3CH2OH`, we can follow these steps:

### Step 1: Identify the Reactants
The reactants in the reaction are:
- **CH3CHO**: This is acetaldehyde, which is an aldehyde.
- **LiAlH4**: This is lithium aluminum hydride, a strong reducing agent.

### Step 2: Understand the Role of the Reducing Agent
Lithium aluminum hydride (LiAlH4) is known for its ability to donate hydride ions (H⁻). In this reaction, LiAlH4 acts as a reducing agent, which means it will add hydrogen to the carbonyl compound (acetaldehyde).

### Step 3: Identify the Electrophile
In the reaction, the carbonyl carbon (C=O) of the aldehyde is electron-deficient due to the electronegativity of oxygen, which pulls electron density away from the carbon. This makes the carbon atom a good electrophile.

### Step 4: Identify the Nucleophile
The nucleophile is an electron-rich species that can donate a pair of electrons to form a bond with the electrophile. In this case, the hydride ion (H⁻) from LiAlH4 is the nucleophile. It attacks the electron-deficient carbonyl carbon of the aldehyde.

### Step 5: Describe the Mechanism
1. The hydride ion (H⁻) attacks the carbonyl carbon of acetaldehyde (CH3CHO).
2. This results in the formation of a tetrahedral intermediate where the carbonyl bond breaks.
3. The oxygen atom of the intermediate carries a negative charge.
4. The intermediate is then protonated (usually by water in a workup step) to form the final product, ethanol (CH3CH2OH).

### Conclusion
The nucleophile added in the reaction is the **hydride ion (H⁻)** from lithium aluminum hydride (LiAlH4).

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