title: Favoured conformations of methyl isopropyl, ethyl isopropyl, methyl tert-butyl, and ethyl tert-butyl 2-(triphenylphosphoranylidene)malonate.
abstract: The conformations of organic compounds determined in the solid state are important because they can be compared with those in solution and/or from theoretical calculations. In this work, the crystal and molecular structures of four closely related diesters, namely methyl isopropyl 2-(triphenylphosphoranylidene)malonate, C(25)H(25)O(4)P, ethyl isopropyl 2-(triphenylphosphoranylidene)malonate, C(26)H(27)O(4)P, methyl tert-butyl 2-(triphenylphosphoranylidene)malonate, C(26)H(27)O(4)P, and ethyl tert-butyl 2-(triphenylphosphoranylidene)malonate, C(27)H(29)O(4)P, have been analysed as a preliminary step for such comparative studies. As a result of extensive electronic delocalization, as well as intra- and intermolecular interactions, a remarkably similar pattern of preferred conformations in the crystal structures results, viz. a syn-anti conformation of the acyl groups with respect to the P atom, with the bulkier alkoxy groups oriented towards the P atom. The crystal structures are controlled by nonconventional hydrogen-bonding and intramolecular interactions between cationoid P and acyl and alkoxy O atoms in syn positions.
authors.affiliation: Departamento de Química Orgánica y Fisicoquímica, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Casilla 233, Santiago, Chile. fcastane@ciq.uchile.cl
authors.forename: Fernando
authors.initials: F
authors.lastname: Castañeda
authors.forename: Paul
authors.initials: P
authors.lastname: Silva
authors.forename: Clifford A
authors.initials: CA
authors.lastname: Bunton
authors.forename: María Teresa
authors.initials: MT
authors.lastname: Garland
authors.forename: Ricardo
authors.initials: R
authors.lastname: Baggio
mesh_terms: D003461:Crystallography; D008314:Malonates / Q000737:chemistry*; D008968:Molecular Conformation; D009943:Organophosphorus Compounds / Q000737:chemistry*
chemical_list: D008314:Malonates; D009943:Organophosphorus Compounds