An ab initio study of the relationship between the OH bond length and the harmonic and anharmonic stretching force constants for planar molecules containing COH, NOH, and OOH groups

Abstract

AbstractThe OH bond length and the quadratic, cubic, and quartic stretching force constants, calculated ab initio using the unscaled 4‐31G basis set with full geometry optimization, are reported for 30 planar conformers of ten molecules contaning either the COH, NOH, or OOH group. The data are analyzed in terms of the general form of Clark's equation, and the power functions and exponential functions proposed by Herschbach and Laurie. In the case of the quadratic constants, significant trends are found in the values of the parameters depending on whether the OH group is bonded to carbon, nitrogen, or oxygen, and whether it is non‐hydrogen‐bonded or involved in intramolecular hydrogen bond formation in four‐, five‐, or six‐membered rings. Using data for diatomic molecules, OH, and CH bonds, and the CO and CC bonds in planar monosubstituted carbonyl compounds, the parameter dij in the power function equation for quadratic constants, which can be regarded as the distance of closest approach of the two nuclei, is shown to increase progressively along the series (i) diatomic molecule; (ii) similar bond in a polyatomic environment with one of the two atoms covalently bonded to a neighboring atom; (iii) as in (ii) but with the second atom hydrogen bonded; and (iv) with both atoms covalently bonded to neighboring atoms.