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

The CO bond length and fCO,CO, the corresponding harmonic stretching force constant, are calculated ab initio using the 4‐31G basis set (augmented by polarization functions on the sulfur and chlorine) with full geometry optimization for the monosubstituted carbonyl compounds RCHO, where R = H, CHO, CHCH2, CO2H, CHCHOH, OH, OC(O)OH, OOH, SH, Li, F, Cl, and NH2. Straight‐line relationships are found in plots of ln[fCO,CO] vs. ln[rCO] for the series of compounds in which carbon atoms and oxygen atoms are bonded directly to the carbonyl carbon, in accordance with the empirical expression f = C′/rn. The slopes and intercepts give n = 7.62 and 6.47, C′ = 62.6 and 48.6, for the lines with carbon and oxygen as the atom bonded directly to the carbonyl carbon, respectively. The point for formaldehyde lies very close to the C line, whereas the points for SH, Li, F, Cl, and NH2 lie closer to the O line.