Wittig olefination

A phosphorus ylide replaces the carbonyl oxygen with its own carbon, giving the alkene.

mechanism writtenBalanced: every atom is accounted for

What it needs, and what it gives

Reaction class: Olefination
Typical conditions: The ylide is made from the phosphonium salt with a base. The phosphine oxide is the driving force.
Mass balance: balanced — the co-products are written out, not dropped
Mechanism: Wittig olefination, 3 steps

Conditions are what the literature ordinarily uses, recorded so you can see whether yours are in the usual range. They are not a procedure and they are not scaled to your flask.

How it is thought to happen

The ylide adds to the carbonyl, the four-membered ring that results falls apart the other way, and the phosphorus leaves with the oxygen.

The ylide carbon attacks the carbonyl
The oxygen closes onto the phosphorus
The ring falls apart the other way

This is the pathway taught for the class, not a record of what was observed. On the platform it is drawn on the structures you supply, with the curly arrows on the atoms that actually move.

Read the Wittig olefination mechanism

Try it on your own structures

Enter your reactants in the Reaction Lab. If this transformation matches what you drew, it is applied and the outcome is shown next to the records that back it — with the count of documented reactions doing the same thing on substrates like yours, rather than a confidence score.

Open the Reaction Lab Browse recorded reactions

Other olefination transformations