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How many of the following ethers CANNOT be synthesised by the Williamson ether synthesis? (1) (CH3)3C-O-C(CH3)3 (2) CH3CH2-O-CH3 (3) CH3-O-CH3 (4) (CH3)3C-O-CH2CH3 (5) C6H5-O-CH3 (6) C6H5-O-C6H5 (7) C6H5-O-CH=CH2 (8) CH2=CH-CH2-O-CH2CH3

1. 1
2. 2
3. 3
4. 4

Correct answer: 2

Solution

Williamson synthesis: R-O⁻ + R'-X -> R-O-R'. SN2 requires a primary or secondary alkyl halide. (1) (CH3)3C-O-C(CH3)3 requires (CH3)3C-X (tertiary) — SN2 blocked. (6) Ph-O-Ph requires Ph-X (aryl halide, no SN2) and Ph-O⁻ + Ph-X fails — blocked. (7) Ph-O-CH=CH2 requires vinyl halide (CH2=CH-X) — SN2 blocked. All others can be synthesised. So three ethers cannot be made: (1), (6), (7).

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