As a result of earlier interest in the calculation of the C-H nuclear spin-spin coupling constants and its correlation with the C-H stretching frequencies in hydrocarbons and heterosubstituted hydrocarbons, a novel general relationship for the calculation of the C-H stretching frequencies is proposed in this paper. The proposed relationship has been employed to calculate the C-H stretching frequencies (nCH) for a series of hydrocarbons, fluorosubstituted hydrocarbons and substituted aldehydes by use of the CNDO/2 MO approximation and the natural hybrid orbital scheme. It is shown that the C-H stretching frequencies are directly proportional to the s-character of the corresponding C atom in hydrocarbons. But for heterosubstituted hydrocarbons, the net charges of atoms C and H, or the polarity of the C-H bond, become a significant factor. The calculated results may also be utilized to account for other factors affecting nCH, such as steric effect, cis-trans geometry and substituted effects etc. Some discussions concerning the calculated results are also reported.

Key words: CNDO APPROXIMATION, CHEMICAL BONDS, MOLECULAR ORBITAL THEORY, HYBRID ORBITAL, HYDROCARBAN