Abstract

The crystal structures of four alkyl 3-oxo-2-(triphenyl-phosphoranylidene)butyrates, where the alkyl group is methyl (C 23H 21O 3P·0.5C 6H 6), (II), ethyl (C 24H 23O 3P), (III), isopropyl (C 25H 25O 3P), (IV), or tert-butyl (C 26H 27O 3P), (V), shows all of them to have the same conformation. They present a tetrahedral P atom and an sp 2 ylidic C atom, with the carbonyl groups adopting anti conformations with respect to the keto groups located close to the P atom. P-C-C-O torsion angles, bond lengths and angles indicate an effective electronic delocalization toward the keto groups. In each case, one H atom of the alkoxy group is close to one of the phenyl rings. These preferred conformations are evaluated as the result of attractive and repulsive intramolecular interactions.