Question

The halogen compound which will not react with phenol to give ethers is

• A. ethyl chloride
• B. methyl chloride
• C. benzyl chloride
• D. vinyl chloride
• E. allyl chloride

Hint:

Vinyl halides and aryl halides are "twins" when it comes to being non-reactive in substitution reactions.

Answer 1

The Correct Option is D

Concept: Preparation of ethers from phenol usually involves reacting a phenoxide ion (\(C_6H_5O^-\)) with an alkyl halide (Williamson Ether Synthesis). This is a nucleophilic substitution reaction (\(S_N2\)).

Step 1: Examine the reactivity of the halides.
Options (A), (B), (C), and (E) are all reactive toward nucleophiles.
• Methyl and Ethyl chlorides are simple primary halides.
• Benzyl and Allyl chlorides are exceptionally reactive because their transition states are stabilized by resonance.

Step 2: Analyze Vinyl Chloride (D).
In vinyl chloride (\(CH_2=CH-Cl\)), the chlorine is attached to an \(sp^2\) hybridized carbon.
• Just like in chlorobenzene, the lone pair on Chlorine is in resonance with the double bond: \(CH_2=CH-Cl \leftrightarrow ^-CH_2-CH=Cl^+\).
• This creates a partial double bond character in the C-Cl bond, making it very strong and difficult to break.
• Nucleophilic attack on an \(sp^2\) carbon is also electronically disfavored.