The Mills—Nixon and anomeric effects in 2,3-dihydro-1H-1,3,2-benzodiazaphospholes: a gas-phase electron diffraction study of C6H4(NMe)2PCl using quantum-chemical data and “a priori” force field

Abstract

Geometric parameters and the force fields of the molecule of 2-chloro-1,3-dimethyl-2,3-dihydro-1H-1,3,2-benzodiazaphosphole, C6H4(NMe)2PCl (1), and the 1,3-dimethyl-2,3-dihydro-1H-1,3,2-benzodiazaphospholium cation, C6H4(NMe)2P+ (2), containing a dicoordinated P atom were calculated by the restricted Hartree—Fock (RHF) method using the 6-31G* and 6-311G** basis sets. Vibrational characteristics of the internuclear distances in molecule 1 were calculated using the “a priori” scaled force field. Structural analysis of the gas-phase electron diffraction data for this molecule was performed with inclusion of nonlinear kinematic effects at the first-order level of perturbation theory. Substantial lengthening of the P—Cl bond and conformational peculiarities of the phosphole fragment of molecule 1 are consistent with the expected manifestations of the anomeric effect. The type of partial localization of the π-bonds in the benzene fragment (relative weights of two resonance Kekule structures, or the Mills—Nixon effect) changes on going from covalent to ionized state of the P atom in the annelated five-membered ring.