Wittig Reaction - Addition/Elimination from aldehydes and ketones

In 1954 Georg Wittig reported an alkene synthesis reaction from carbonyl compounds using phosphonium ylides (phosphoranes) - the synthesis is known as the Wittig reaction:


An ylide is a molecule with an adjacent positive and negative charge, and are formed by the removal of a proton from the carbon adjacent to a positively charged heteroatom (P+, S+ or N+).
Ylides are most conveniently prepared in a two-step synthesis from haloalkanes.