Reaction Scheme
aldehyde or ketone + phosphonium ylide -> alkeneOften run in ether, THF, or hydrocarbon solvents depending on ylide stability.
Primary reaction SMILES: O=Cc1ccccc1.C=P(c1ccccc1)(c1ccccc1)c1ccccc1>>C=Cc1ccccc1
Organic reaction
Wittig Reaction
The Wittig reaction converts aldehydes or ketones into alkenes using a phosphonium ylide. It is one of the most searched named reactions for alkene synthesis.
Two Common Examples
Benzaldehyde to styrene
Benzaldehyde plus methylene ylide gives styrene.
Cyclohexanone olefination
Cyclohexanone can be converted to methylenecyclohexane.
MolDraw Use
Open the reaction in MolDraw to edit reactant labels, add conditions, or export a clean scheme.
How It Works
The Wittig reaction converts an aldehyde or ketone into an alkene. A phosphonium salt, made from triphenylphosphine and an alkyl halide, is deprotonated by a strong base to give a phosphorus ylide (Ph3P=CHR). The ylide adds to the carbonyl to form a four-membered oxaphosphetane, which breaks down to the alkene and triphenylphosphine oxide. The very strong P=O bond formed drives the reaction.
Conditions and Scope
- Non-stabilised ylides (R = alkyl) tend to give Z-alkenes.
- Stabilised ylides (R = ester, ketone, nitrile) tend to give E-alkenes.
- The C=C forms exactly where the C=O was, so there is no ambiguity about double-bond position, unlike elimination reactions.
- The Horner–Wadsworth–Emmons variant uses phosphonate carbanions and usually gives E-alkenes with water-soluble by-products.
FAQ
Example: benzaldehyde + Ph3P=CH2 gives styrene and Ph3P=O. How do I draw it? Show the ylide in both resonance forms if you are teaching the mechanism, draw the oxaphosphetane intermediate in brackets, and show E or Z geometry explicitly on the product.