SUBSTITUENT EFFECTS ON BASICITY IN GROUP-15 COMPOUNDS - AN ANALYSIS BASED ON PROTON AFFINITIES, CHARGE-DISTRIBUTIONS, AND DIPOLE POLARIZABILITIES

Ab initio calculations on a series of trisubstituted amines, phosphine s, and arsines are presented at the MP2/6-311G(d,p) level. Specificall y, the species studied are XH3, XF3, and X(Me)(3), where X = N, P, or As. The influence of the substituents on the proton affinity is analyz ed in terms of the charge distribution, its topology, some one-electro n properties (dipole moments, electric field gradients), and dipole po larizabilities. An atoms-in-molecules decomposition of the charge dist ribution, energetics, and polarizabilities also proves informative. Th ere seems to be no straightforward way of rationalizing the basicities of these compounds on the basis of electrostatic properties (i.e., pr operties of the charge distribution in the unprotonated bases). Howeve r, substituent effects on basicities can be correlated with response p roperties, such as the molecular (and atoms-in-molecules) polarizabili ty tensors, and the amount of charge that a substituent group or atom donates on protonation.