| Abstract
| - The geometries and thermodynamic properties (ΔHf298, S298, and Cp(T) (300−1500 K)) of 45 ketenes of fourdifferent types namely alkylketenes (set I), oxygenated alkylketenes (set II), 1,2- and 1,3-bisketenes (set III),and ketene-substituted alcohols (set IV) were determined by means of the CBS-Q procedure. The heats offormation of oxygenated ketenes were reevaluated using isodesmic reactions, and a systematic and consistent(∼1.5 kcal/mol) over prediction in the stability of tert-butyl substituted systems has been identified at theCBS-Q level. Nearly 20 new thermochemical groups for the ketene molecular family and 3 nonnext neighborinteraction terms were evaluated from the computed thermodynamic functions by simultaneous parameterestimation. The nonnext neighbor corrections account for an eclipsing interaction between the >CCO groupand its β bonds. Statistical analysis of the ab initio data demonstrates the validity of the group additivityapproximation. The derived group values describe the ab initio ΔHf298, S298, and Cp(300 K) with an averagedeviation of less than 0.06 kcal/mol, 0.15 cal/(mol K), and 0.18 cal/(mol K), respectively. In most cases,these quantum-calibrated group additivity estimates are expected to be more accurate than the limitedexperimental data and empirical estimates; the only significant discrepancy (∼1.5 kcal/mol) is for substitutedketenes containing a tert-butyl group.
|
