An ab initio study of the influence of substituents and intramolecular hydrogen bonding on the carbonyl bond length, and the harmonic and anharmonic stretching force constants. I. Monosubstituted carbonyl compounds

Abstract

The CO 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 three series of monosubstituted carbonyl compounds in which the atom directly bonded to the carbonyl carbon is another carbon, a nitrogen, or an oxygen atom, respectively. The data are analyzed in terms of the In ƒ versus In r e relationship, and also the generalized power functions and exponential functions proposed by Herschbach and Laurie. Not only does the atom directly bonded to the carbonyl carbon affect the magnitude of r e and the force constants, but the rest of the substituent group is found to be capable of exerting an even greater influence. Within each series of compounds the overall progression from the shortest to the longest CO bonds is tentatively attributed to a diminishing electron density in the bonding region.