Which of the following ethers cannot be prepared by Williamson ether synthesis?

Step-by-step solution

Williamson ether synthesis involves an S_ N 2 reaction between an alkoxide or aroxide ion and an alkyl halide. For the S_ N 2 reaction to proceed successfully, the alkyl halide must have the halogen attached to an sp³ hybridized carbon (preferably primary or methyl). In option (A), CH ₂= CH - CH ₂- O - CH ₃ can be prepared by reacting sodium methoxide with allyl halide, or sodium allyloxide with methyl halide. In option (B), CH ₃- CH = CH - O - CH = CH ₂ has oxygen bonded to two sp² hybridized vinylic carbons. Its