Methyl, ethyl, isopropyl and tert-butyl 3-oxo-2-(triphenylphosphoranylidene)butyrates, a common pattern a preferred conformation
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The crystal structures of four alkyl 3-oxo-2-(triphenylphosphoranylidene)butyrates, where the alkyl group is methyl (C23H21O3P .0.5C(6)H(6)), (II), ethyl (C24H23O3P), (III), isopropyl (C25H25O3P), (IV), or tert-butyl (C26H27O3P), (V), show 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.