Consider the reaction
`RCHO + NH_(2)NH_(2) rarr R - CH = N NH_(2)`
What sort of reaction is it?

Options

A. Electrophilic addition - elimination reaction
B. Free radical addition - elimination reaction
C. Electrophilic substitution - elimination reaction
D. Nucleophilic addition - elimination reaction

Answer

To determine the type of reaction occurring in the given equation:

**Reaction:**
\[ RCHO + NH_2NH_2 \rightarrow R-CH=N-NH_2 \]

### Step-by-Step Solution:

1. **Identify the Reactants:**
- The reactants in the reaction are an aldehyde (RCHO) and hydrazine (NH2NH2).
- Aldehydes contain a carbonyl group (C=O) and are known for their reactivity with nucleophiles.

2. **Nucleophilic Addition:**
- The nitrogen atom in hydrazine (NH2) acts as a nucleophile and attacks the electrophilic carbon atom of the carbonyl group (C=O) in the aldehyde.
- This results in the formation of a tetrahedral intermediate where the carbonyl oxygen becomes an alcohol (–OH) and the nitrogen from hydrazine is added to the carbon.

3. **Formation of the Intermediate:**
- The intermediate formed after the nucleophilic addition can be represented as:
\[ R-CH(OH)-N(NH_2) \]
- Here, the carbon is bonded to an –OH group and the hydrazine moiety.

4. **Elimination of Water:**
- The next step involves the elimination of a water molecule (H2O) from the intermediate.
- This occurs as the hydroxyl group (–OH) and a hydrogen atom from the nitrogen (NH2) are removed, leading to the formation of a double bond between carbon and nitrogen.

5. **Final Product Formation:**
- After the elimination of water, the final product is a hydrazone:
\[ R-CH=N-NH_2 \]
- This structure features a carbon-nitrogen double bond and is characteristic of hydrazones.

6. **Conclusion:**
- The overall reaction involves two main steps: nucleophilic addition followed by elimination (specifically, the elimination of water).
- Therefore, the type of reaction can be classified as a **nucleophilic addition-elimination reaction**.

### Final Answer:
The reaction is a **nucleophilic addition followed by elimination**.

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