A ylide with an electron drawing group will result in trans geometry of the product alkene.

Question

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Ylides with electron-donating groups such as phosphonium ylides or sulfonium ylides typically result in trans geometry of the product alkene due to the Felkin-Anh model. The electron-donating group on the ylide serves as a nucleophile, attacking the electrophilic carbon of the carbonyl group in the substrate. The resulting transition state leads to preferential formation of the trans product.

A Ylide with an Electron Drawing Group Will Result in Trans