IR spectroscopy as a source of data on bond strengths

Abstract

The aim of this work is the estimation of double bond strength, namely CO bonds in ketones and aldehydes and CC bonds in various compounds. By the breaking of these bonds one or both fragments formed are carbenes, for which experimental data on the enthalpies of formation (ΔHf298) are scarce. Thus for the estimation of ΔHf298 of the corresponding carbenes, the empirical equations were proposed based on different approximations. In addition, a quantum chemical calculations of the ΔHf298 values of carbenes were performed, and the data obtained were compared with experimental values and the results of earlier calculations.Equations for the calculation of CO bond strengths of different ketones and aldehydes from the corresponding stretching frequencies ν(CO) were derived. Using the proposed equations, the strengths of CO bonds of 25 ketones and 12 conjugated aldehydes, as well as CC bonds of 13 hydrocarbons and 7 conjugated aldehydes were estimated for the first time. Linear correlations of CC and CO bond strengths with the bond lengths were established, and the equations permitting the estimation of the double bond strengths and lengths with acceptable accuracy were obtained. Also, the strength of central CC bond of stilbene was calculated for the first time. The uncertainty of the strengths of double bonds obtained may be regarded as accurate ±10–15 kJ/mol.