The Wittig reaction forms alkenes from aldehydes or ketones using what reagent?

The Wittig reaction forms alkenes from aldehydes or ketones using what reagent?

• A. Phosphonium ylides
• B. Grignard reagents
• C. Hydrogen gas
• D. Catalysts

Answer: (A)

The Wittig reaction uses phosphonium ylides to convert aldehydes or ketones into alkenes. A phosphonium salt is converted into a phosphorus-centered ylide, which then reacts with a carbonyl compound to form an oxaphosphetane intermediate that collapses to give the alkene and triphenylphosphine oxide. This reagent is central because it brings in the phosphorus-containing fragment that ultimately leaves as phosphine oxide, driving the formation of the carbon–carbon double bond. Grignard reagents add to carbonyls to give alcohols after workup, not alkenes; hydrogen gas is used for hydrogenation, not constructing alkenes from carbonyls; and catalysts alone don’t supply the specific leaving-phosphine oxide step that defines the Wittig process.

The Wittig reaction uses phosphonium ylides to convert aldehydes or ketones into alkenes. A phosphonium salt is converted into a phosphorus-centered ylide, which then reacts with a carbonyl compound to form an oxaphosphetane intermediate that collapses to give the alkene and triphenylphosphine oxide. This reagent is central because it brings in the phosphorus-containing fragment that ultimately leaves as phosphine oxide, driving the formation of the carbon–carbon double bond. Grignard reagents add to carbonyls to give alcohols after workup, not alkenes; hydrogen gas is used for hydrogenation, not constructing alkenes from carbonyls; and catalysts alone don’t supply the specific leaving-phosphine oxide step that defines the Wittig process.