Effect on dipoles

Isotope Effects on Dipole Moments, Polarizability, NMR Shielding, and Molar Volume... 

Abstract Although the electronic structure and the electrical properties of molecules in first approximation are independent of isotope substitution, small differences do exist. These are usually due to the isotopic differences which occur on vibrational averaging. Vibrational amplitude effects are important when considering isotope effects on dipole moments, polarizability, NMR chemical shifts, molar volumes, and fine structure in electron spin resonance, all properties which must be averaged over vibrational motion. 

Inductive effects on dipole moments and the effects of intervening atoms on electrostatic interaction energies are represented by polarizability centers In conjunction with bond centered dipoles. Solvation energies are estimated by means of a continuum dlpole-quadrupole electrostatic model. Calculated energies of a number of conformations of meso and racemic 2,4-dichloropentane and the iso, syndio, and hetero forms of 2,4,6-triehloroheptane give satisfactory representations of isomer and conformer populations. Electrostatic effects are found to be quite important. 

The 4-3IG basis set is not exactly a double zeta basis since only the valence functions are doubled and a single function is still used for each inner shell orbital. It may be termed a split valence shell basis set. The inner shells contribute little to most chemical properties and usually vary only slightly from molecule to molecule. Not splitting the inner shell functions has some effect on the total energy, but little effect on dipole moments, valence ionization potentials, charge densities, dissociation energies, and most other calculated quantities of chemical interest. The 4-3IG basis thus consists of 2 functions for H and He, 9 functions for Li to Ne, 13 functions for Na to Ar,..., etc. For hydrogen the contractions are... 

Reid JD, Lawrence WH, Buck RP. Dielectric properties of an epoxy resin and its composite 1. Moisture effects on dipole relaxation. J Appl Polym Sci 1986 30 1771. 

Prop. Spectra IR (957), (far) IR, Raman and assignment (I3I5, 208l), NMR (259, 582, 735, 1821), microwave (957, 1556), Coriolis coefficient and ground state centrifugal distortions (869), dipole moment (582), deuterium effect on dipole moment (1556), nonbonded electron effect on internal rotation (II6I), electrostatic model to treat hindered rotation force constant (I38,... 

In real molecules both terms will contribute. Buckingham (24) has recently considered the relation between dipole derivatives and isotope effects on dipole moment. For HCl, using modem spectroscopic data that requires (dju/dr) to be positive, he calculates a dipole moment difference Ap = —0.0039D, arising largely from the linear term, the square teim reducing the difference by some ten percent. The situation thus looks like that in Fig. 1(b), but with much more gentle curvature. In just this case—and HCl is one of the very few molecules for which adequate data for the calculation exists—there is an unfortunate unresolved discrepancy between theory and experi-... 

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