Thermochemistry of organic and heteroorganic species. Part XIII. Interrelationship for nCH 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 DnCH values equivalent for 1 kcal in DBDE (bond dissociation energy) R–H/R0–H was applied: 9 cmK1 in alkanes, 11 cmK1 in alkenes RCHaCH–H (RCHaCH2), 12 cmK1 in alkynes RCbC–H, and 14 cmK1 in RCHaO molecules. It was found that in halogenated methanes and some other molecules (CH3SH, CH3PH2, CH3NO2, CH3ONO2) the registered nCH value is much higher than it is expected from BDEs bC–H. The expected nCH frequencies were calculated for about 25 molecules. q 2004 Published by Elsevier B.V.