A Wittig reaction between benzaldehyde and methylidenetriphenylphosphorane yields which product?

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Multiple Choice

A Wittig reaction between benzaldehyde and methylidenetriphenylphosphorane yields which product?

The key idea is that a Wittig reaction forms an alkene by linking the carbonyl carbon of the aldehyde with the methylene carbon of the phosphorane ylide. Here, the ylide is methylidenetriphenylphosphorane, which provides a CH2 unit. When it reacts with benzaldehyde, that CH2 becomes the terminal carbon of the new double bond, while the carbonyl carbon becomes the other alkene carbon. The result is a vinyl benzene product, i.e., styrene (Ph–CH=CH2). The reaction also kicks out triphenylphosphine oxide as a byproduct. The other options don’t fit this pattern: benzaldehyde would not remain unchanged, benzyl alcohol would come from reduction rather than a Wittig alkene-forming step, and ethyl benzoate would require forming an ester, not an alkene, product.

The key idea is that a Wittig reaction forms an alkene by linking the carbonyl carbon of the aldehyde with the methylene carbon of the phosphorane ylide. Here, the ylide is methylidenetriphenylphosphorane, which provides a CH2 unit. When it reacts with benzaldehyde, that CH2 becomes the terminal carbon of the new double bond, while the carbonyl carbon becomes the other alkene carbon. The result is a vinyl benzene product, i.e., styrene (Ph–CH=CH2). The reaction also kicks out triphenylphosphine oxide as a byproduct.

The other options don’t fit this pattern: benzaldehyde would not remain unchanged, benzyl alcohol would come from reduction rather than a Wittig alkene-forming step, and ethyl benzoate would require forming an ester, not an alkene, product.

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