Organic Reaction Analysis: Product Identification

This question involves identifying product 'B' formed in a multi-step organic reaction sequence. The starting compound is a cyclic ketone undergoing specific transformations.

Step-by-Step Solution:

Step 1: Analyze the Starting Compound
The reactant is cyclohexanone: $(C_{6} H_{10} O)$ , a six-membered cyclic ketone.

Step 2: Identify Reaction 1 (Conversion to A)
The first reagent is $N H 2 N H 2$ (hydrazine). This is a classic Wolff-Kishner reduction.
Reaction: $C = O \overset{N H 2 N H 2}{\to} C H 2$
The carbonyl group (C=O) is reduced to a methylene group (CH₂).
Product A: Cyclohexane $(C_{6} H_{12})$ .

Step 3: Identify Reaction 2 (Conversion of A to B)
The second reagent is $B r_{2} / h ν$ (Bromine with light/heat). This indicates a free radical bromination reaction.
Cyclohexane is a saturated hydrocarbon. Under these conditions, bromination occurs at the allylic position (if available) or via substitution at a tertiary carbon. However, cyclohexane has no tertiary carbons; all carbons are equivalent secondary carbons.
The reaction proceeds via a free radical mechanism, replacing a hydrogen atom with a bromine atom.
Product B: Bromocyclohexane $(C_{6} H_{11} B r)$ .

Final Answer: The structure of product B is Bromocyclohexane. Among the options, this corresponds to the structure:

Related Topics & Formulae

1. Wolff-Kishner Reduction:
General Reaction: $R -_{1} C O R -_{2} \overset{1 . N H 2 N H 2 2 . O H -, Δ}{\to} R -_{1} C H_{2} R -_{2}$
Mechanism: Formation of a hydrazone intermediate followed by decomposition under basic conditions to yield the alkane.

2. Free Radical Halogenation:
General Reaction: $R - H + X 2 \overset{h ν}{\to} R - X + H X$ (where X = Cl, Br)
Mechanism: Involves three steps - Initiation, Propagation, and Termination. Bromination is more selective than chlorination and prefers tertiary > secondary > primary hydrogens.

3. Key Theory:
The order of reactivity for free radical bromination is guided by the stability of the radical formed. Tertiary radicals are most stable, followed by secondary, and then primary. In symmetric molecules like cyclohexane, a single monosubstituted product is formed.