Thermochemistry of organic and heteroorganic species. Part XIII. Interrelationship for nu(CH) values in RH molecules and enthalpy of formation of R-center dot free radicals in aliphatic compounds

摘要

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 Deltav(CH) values equivalent for 1 kcal in DeltaBDE (bond dissociation energy) R-H --> R'-H was applied: 9 cm(-1) in alkanes, 11 cm(-1) in alkenes RCH=CH-H (RCH=CH2), 12cm(-1) in alkynes RCdropC-H, and 14cm(-1) in RCH=O molecules. It was found that in halogenated methanes and some other molecules (CH3SH, CH3PH2, CH3NO2, CH3ONO2) the registered v(CH) value is much higher than it is expected from BDEs dropC-H. The expected v(CH) frequencies were calculated for about 25 molecules. (C) 2004 Published by Elsevier B.V.