Thermochemical characteristics of organic and organoelement species: X. Formation enthalpy of fragments from ionized cyclopropenes

The advantages of isodesmic reaction series application to estimation of fo rmation enthalpies for cations in gas phase are fully considered. This tech nique applied to thermochemistry of ions obtained at photoionization of ii substituted cyclopropenes provided a possibility to estimate formation enth alpy values for 80 hydrocarbon and 65 heteroatomic ions, in particular, sub stituted benzyl ions, cyclopropenylium and tropylium ions. The isodesmic re action series procedure may serve as an alternative for certain theoretical and even experimental (especially mass spectrometry) methods of evaluating DeltaH(f)(0) values. From experimental appearance potentials were determin ed the DeltaH(f)(0) for ethynyl, trichlorocyclopropenylium, and ethynyl-tro pylium ions (1268, 1041, and 1041 kJ mol(-1), respectively).