Ylides

An ylide or ylids is a neutral, dipolar molecule with both of its atoms having complete octets of electrons. It typically consists of a heteroatom with a formal positive charge (often nitrogen, phosphorus, or sulphur) immediately connected to a nominally negatively charged atom. As a result, two nearby atoms are joined together by both an ionic and a covalent connection, forming a structure. As a result, ylides are 1,2-dipolar molecules and a type of zwitterions. As reagents or reactive intermediates, they can be found in organic chemistry. The Wittig reaction, a technique for converting ketones and specifically aldehydes to alkenes, makes use of phosphonium ylides. A phosphorus atom with three phenyl substituents and a link to a carbanion carries the positive charge in these Wittig reagents.