X-ray investigations of sulfur-containing fungicides. III. Intramolecular forces governing the conformation of a novel orthorhombic polymorph of benzoylmethyl phenyl sulfone, benzoylmethyl 4-chlorophenyl sulfone and benzoylphenylmethyl phenyl sulfone

Abstract

The crystal and molecular structures of three beta-ketosulfones: benzoylmethyl phenyl sulfone (I), benzoylmethyl 4-chlorophenyl sulfone (II) and benzoylphenylmethyl phenyl sulfone (III) have been investigated using X-ray analysis and quantum mechanics ab initio calculations. Compound (I) crystallizes in the monoclinic and orthorhombic crystal systems. The crystal structure of the orthorhombic polymorph has not been reported previously. At room temperature and in the presence of daylight the pale yellow orthorhombic crystals undergo transformation to the stable colourless monoclinic polymorph. Hyperconjugative sigma(S-C1) - pi(*)(C2=O3) and sigma(*)(S-C1) - pi(C2=O3) stabilization energies in benzoylmethyl phenyl sulfones are highly dependent on the central dihedral angle alpha: S-C1-C2=O3 and are largest for a gauche arrangement, as found in both crystal forms of (I). The electron density distribution in all compounds (I), (II) and (III) is significantly affected by interactions of oxygen lone pairs with non-bonding orbitals of the adjacent S-C1 and C1-C2 bonds. The latter effect is responsible for back-donation of the electron density from O atoms towards the central part of the molecule.