Abstract
The magnitudes and trends of the dipole moments of Me xH 3-xE and Me xH 3-xEBH 3 (E = N, P; x = 0→3; Me = CH3) were investigated via CNDO-MO methods. Moments evaluated by the CNDO/2D approach reproduced the experimental data better than the strict CNDO/2 formalism. Transformation of the canonical CNDO/2 MO's to localized MO's (LMO's) permitted a partitioning of the total moments into bond moments, bond polarization moments, and lone pair moments. Values of the lone pair moments of the phosphines are calculated to be greater than those of the amines. Within the framework of the CNDO/2D approximation, coordination of BH3 to H3N involves a charge migration primarily between the N-bound and B-bound hydrogens (0.33e) while coordination to H 3P is primarily P → B (0.27e). The covalent character of the BN and BP bonding LMO's is 46 and 61%, respectively. The CNDO molecular orbital results are in general agreement with Weaver and Parry's model for dipole moments and base strengths of amines and phosphines.
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