Advanced Topic 840 of 1102 Organic Chemistry
Wittig Reaction
Converts aldehydes or ketones into alkenes using phosphorus ylides.
In-depth explanation of Wittig Reaction
The Wittig reaction converts an aldehyde or ketone into an alkene by reaction with a phosphorus ylide, Ph3P=CHR. The ylide carbon attacks the carbonyl carbon, and a four-membered oxaphosphetane intermediate forms and collapses to give the alkene and triphenylphosphine oxide. The strong phosphorus-oxygen bond formed drives the reaction. The position of the new double bond is fixed where the carbonyl was, which gives precise control of alkene placement. Stabilized ylides tend to give E alkenes, while unstabilized ylides give mainly Z alkenes.
Going deeper: Wittig Reaction
Key ideas: Phosphonium ylide (Ph3P=CHR from Ph3P, alkyl halide and strong base like BuLi) converts aldehydes or ketones to alkenes, with Ph3P=O as by-product, driven by the very strong P-O bond (about 540 kJ/mol). Unstabilised ylides give mainly Z alkenes, stabilised ylides (with adjacent C=O) give E alkenes. The double bond location is fixed exactly where the carbonyl was.
Common mistakes and connections: Students expect the Wittig reaction with ketones and stabilised ylides to work smoothly; hindered ketones are slow. Another error is predicting mixtures of positions, when the position is certain. Triphenylphosphine oxide is hard to remove, one reason for the Horner-Wadsworth-Emmons alternative. Links to carbonyl addition, stereoselective alkene synthesis and E-Z notation.
Visualization of Wittig Reaction
The ylide adds to the carbonyl forming an oxaphosphetane, which collapses to alkene plus very stable triphenylphosphine oxide. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Methylenetriphenylphosphorane, Ph3P=CH2, reacts with cyclohexanone to give methylenecyclohexane.
Frequently asked questions about Wittig Reaction
What is Wittig Reaction?
Converts aldehydes or ketones into alkenes using phosphorus ylides.
Is Wittig Reaction a beginner, intermediate or advanced topic?
Wittig Reaction is a advanced topic in Organic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Wittig Reaction?
Study these earlier topics in Organic Chemistry first: Retrosynthesis, Protecting Groups, Diels-Alder Reaction.
What comes after Wittig Reaction?
The next topics in Organic Chemistry are Claisen Condensation and Michael Addition.
Can I practise Wittig Reaction with quizzes?
Yes. The interactive lesson includes a self-check question on Wittig Reaction, and the Organic Chemistry quiz draws on every topic in this area.
Where Wittig Reaction fits in Organic Chemistry
Wittig Reaction is topic 112 of 148 in Organic Chemistry.