MBOHO CALCULATIONS OF C-H STRETCHING FREQUENCIES IN HYDROCARBONS AND HETEROSUBSTITUTED HYDROCARBONS

Based on the generalized relationship for calculating the nuclear spin -spin coupling constants and the correlation of the bond stretching fr equencies with the coupling constants, a novel generalized relationshi p, which includes the contributions of not only the hybrid orbitals, b ut also the net atomic charges, is introduced for calculation of the b ond stretching frequencies and employed to elucidate the C-H stretchin g frequencies in hydrocarbons and heterosubstituted hydrocarbons on th e basis of the MBOHO calculation employing the CNDO/2 approximation. B y use of the obtained concrete relationships, one can get different nu BAR(CH) value for the C-H bonds existing in different chemical environ ments, which is coincident with chemical intuition. The calculated num erical results show that for hydrocarbons the contribution of the net atomic charges can be neglected, but it is necessary for heterosubstit uted hydrocarbons to include the contribution of the net atomic charge s to the C-H stretching frequencies. The calculated C-H stretching fre quencies are in good agreement with the experimental data, which shows its reasonableness. (C) 1994 John Wiley & Sons, Inc.