Thermochemistry of organic and heteroorganic species. Part XIII. Interrelationship for νCH values in R H molecules and enthalpy of formation of R [rad] free radicals in aliphatic compounds

Abstract

Using IR frequencies for gaseous molecules' R–H bonds, some known values of the enthalpies of formation for carbon-centered R free radicals, and the series of isodesmic reactions, the enthalpies of formation for more than 25 free radicals were found. The variable Δ ν CH values equivalent for 1 kcal in ΔBDE (bond dissociation energy) R–H→R′–H was applied: 9 cm −1 in alkanes, 11 cm −1 in alkenes RCH CH–H (RC H CH 2), 12 cm −1 in alkynes RC C–H, and 14 cm −1 in RC H O molecules. It was found that in halogenated methanes and some other molecules (CH 3SH, CH 3PH 2, CH 3NO 2, CH 3ONO 2) the registered ν CH value is much higher than it is expected from BDEs C–H. The expected ν CH frequencies were calculated for about 25 molecules.