INFRARED INTENSITIES - METHYL HALIDES - EFFECT OF SUBSTITUENTS ON CHARGE-DISTRIBUTIONS

The geometries, force constants, and dipole moment derivatives for methyl fluoride and chloride were calculated using several basis sets. The 4-31G set gave unsatisfactory geometries and dipole moments. The addition of either bond functions or polarization functions led to essentially the same geometrical parameters and dipole moments for both methyl halides which were in agreement with experimental data. Both extended basis sets gave the same dipole moment derivatives which agreed with the experimentally derived values. It is shown that there is a significant difference between the nature of a C-F and a C-CI bond. Fluorine withdraws charge from the carbon, but does not significantly affect the charge on the hydrogen of the methyl fluoride. Chlorine withdraws charges from both the carbon and the hydrogen in methyl chloride. The dipole moment derivatives are discussed in terms of a rehybridization model. © 1979, American Chemical Society. All rights reserved.