Question

Which among the following is benzylic halide?

• A. 4-Iodotoluene
• B. 1-Iodo-2-phenylethane
• C. Iodobenzene
• D. Iodophenylmethane

Hint:

Always distinguish between an aryl halide and a benzylic halide: In aryl halides ($\mathrm{Ar-X}$), the halogen is bound to an $\mathrm{sp^2}$ ring carbon. In benzylic halides ($\mathrm{Ar-C-X}$), the halogen is on a side-chain carbon immediately adjacent to the ring.

Answer 1

The Correct Option is D

Step 1: Fix the definition of a benzylic halide.
In a benzylic halide the halogen sits on an $sp^3$ carbon that is itself joined straight to the benzene ring, that is $Ar-CH_2-X$.
Step 2: Build a quick test.
Trace from the halogen. If the very first carbon carrying $X$ is bonded directly to the ring and is $sp^3$, it is benzylic. If $X$ sits on the ring carbon itself, it is aryl. If a spacer carbon lies between, it is plain aliphatic.
Step 3: Test 4-iodotoluene.
Here iodine is fixed on the aromatic ring carbon ($sp^2$). That is an aryl halide, so reject.
Step 4: Test 1-iodo-2-phenylethane.
Structure $C_6H_5-CH_2-CH_2-I$. The iodine carbon is separated from the ring by one extra $CH_2$, so it is aliphatic, reject.
Step 5: Test iodobenzene.
Iodine is on the ring itself, $C_6H_5I$, an aryl halide, reject.
Step 6: Test iodophenylmethane and conclude.
Structure $C_6H_5-CH_2-I$, also called benzyl iodide. The $sp^3$ carbon bearing iodine is bonded straight to the ring, the exact benzylic pattern.
\[ \boxed{\text{Iodophenylmethane, } C_6H_5CH_2I \text{ (option D)}} \]