Which is the major product of the reaction below? Wittig Reaction

Which is the major product of the reaction below?

Solution:

This is a Wittig reaction since the reagent is (Ph)3P=CHR.

To predict the product, we replace the oxygen in the =O with the CHR group in the Wittig reagent.

This reaction occurs to both aldehydes and ketones. However, aldehydes are more reactive then ketones. That is why, it is the =O on the right side that will react (aldehyde versus ketone on the ring).

We can eliminate choices A and B. Choice C has the double bond in the wrong place. On the starting molecules, we have 3 carbons coming off of the ring followed by the double bond. In choice C, there are 4 carbons followed by the double bond. D is the correct answer.