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

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 ΔνCH 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 RCHCH-H (RCHCH2), 12 cm−1 in alkynes RCC-H, and 14 cm−1 in RCHO molecules. It was found that in halogenated methanes and some other molecules (CH3SH, CH3PH2, CH3NO2, CH3ONO2) the registered νCH value is much higher than it is expected from BDEs C-H. The expected νCH frequencies were calculated for about 25 molecules.