In the following sequence of reactions the maximum number of atoms present in molecule ‘C’ in one plane is________.
A `underset("Cu tube")overset("Red hot") to B underset("Anhydrous" AlCl_(3))overset(CH_(3)Cl "(leq.)")to C ` (A is a lowest molecular weight alkyne).

Answer

To solve the problem step by step, we need to analyze the reactions and the structures involved:

### Step 1: Identify the starting compound (A)
- The problem states that A is the lowest molecular weight alkyne. The simplest alkyne is **acetylene (C₂H₂)**.

### Step 2: Reaction of A (acetylene) in a red-hot copper tube
- When acetylene is passed through a red-hot copper tube, it undergoes **polymerization** to form **benzene (C₆H₆)**. This reaction can be represented as:
\[ 3 \text{C}_2\text{H}_2 \rightarrow \text{C}_6\text{H}_6 \]
- Thus, the product after this step (B) is **benzene**.

### Step 3: Reaction of B (benzene) with CH₃Cl and AlCl₃
- In the next step, benzene reacts with **methyl chloride (CH₃Cl)** in the presence of **anhydrous AlCl₃**, which acts as a Lewis acid. This is a **Friedel-Crafts alkylation** reaction.
- The reaction can be summarized as:
\[ \text{C}_6\text{H}_6 + \text{CH}_3\text{Cl} \xrightarrow{\text{AlCl}_3} \text{C}_7\text{H}_7\text{Cl} \]
- The methyl group (CH₃) attaches to the benzene ring, resulting in **toluene (C₇H₈)**.

### Step 4: Structure of the final product (C)
- The structure of toluene can be represented as:
\[ \text{C}_6\text{H}_5\text{CH}_3 \]
- In this structure, the benzene ring (C₆H₅) has six carbon atoms in a plane, and the methyl group (CH₃) adds one more carbon atom.

### Step 5: Count the number of atoms in one plane
- In the final product (C), we have:
- **Carbon atoms in the plane**: 7 (6 from benzene + 1 from the methyl group)
- **Hydrogen atoms in the plane**: The hydrogen atoms attached to the benzene ring are in the same plane, and the methyl group contributes 3 hydrogen atoms. Thus, there are 6 hydrogen atoms from the benzene and 3 from the methyl group, totaling 9 hydrogen atoms.

### Total atoms in one plane
- Total atoms in the same plane = 7 (C) + 9 (H) = **16 atoms**.

### Final Answer
The maximum number of atoms present in molecule C in one plane is **16**.

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