First product of the reaction between RCHO and `NH_(2) NH_(2)` :-

Options

A. `RCH = N NH_(2)`
B. `RCH = NH`
C. `RCH_(2)NH_(2)`
D. `RCON_(2)`

Answer

To find the first product of the reaction between an aldehyde (RCHO) and hydrazine (NH2NH2), we can follow these steps:

### Step 1: Understand the Reactants
The reactants are an aldehyde (RCHO) and hydrazine (NH2NH2). Aldehydes have the general structure RCHO, where R is an alkyl or aryl group, and hydrazine is a compound with two amino groups connected by a nitrogen (NH2-NH2).

**Hint:** Identify the functional groups present in the reactants to predict how they might interact.

### Step 2: Mechanism of Reaction
The reaction begins with the nucleophilic attack of the nitrogen atom from hydrazine on the carbonyl carbon of the aldehyde. The carbonyl carbon is electrophilic due to the presence of the double bond with oxygen.

**Hint:** Remember that nucleophiles attack electrophiles; here, nitrogen acts as a nucleophile.

### Step 3: Formation of the Tetrahedral Intermediate
When the nitrogen attacks the carbonyl carbon, a tetrahedral intermediate is formed. This intermediate has a negatively charged oxygen (alkoxide) and a positively charged nitrogen.

**Hint:** Visualize the tetrahedral structure to understand how the bonds rearrange during the reaction.

### Step 4: Proton Transfer
In the tetrahedral intermediate, a proton transfer occurs. The positively charged nitrogen loses a proton (H+) to stabilize itself, while the negatively charged oxygen can form a hydroxyl group (OH).

**Hint:** Look for proton transfers in reactions involving charged species to stabilize the molecule.

### Step 5: Elimination of Water
The next step involves the elimination of a water molecule (H2O). The hydroxyl group (OH) and a hydrogen atom from the nitrogen lead to the formation of a double bond between the carbon and the nitrogen.

**Hint:** Water elimination is common in condensation reactions, leading to the formation of double bonds.

### Step 6: Formation of the Hydrazone
The final product of this reaction is a hydrazone, which has the structure RCH=N-NH2. This is the first product formed when an aldehyde reacts with hydrazine.

**Hint:** Recognize the structure of hydrazones, which are characterized by a C=N bond connected to a hydrazine moiety.

### Final Answer
The first product of the reaction between RCHO and NH2NH2 is **RCH=N-NH2** (a hydrazone).