GAS-PHASE AND SOLUTION-PHASE HOMOLYTIC BOND-DISSOCIATION ENERGIES OF H-N+ BONDS ILL THE CONJUGATE ACIDS OF NITROGEN BASES

The oxidation potentials of 19 nitrogen bases (abbreviated as B: six p rimary amines, five secondary amines, two tertiary amines, three anili nes, pyridine, quinuclidine, and 1,4-diazabicyclo[2,2,2]-octane), i.e. , E(ox)(B) values in dimethyl sulfoxide (DMSO) and/or acetonitrile (AN ), have been measured. Combination of these E(ox)(B) values with the a cidity values of the corresponding acids (PKHB+) in DMSO and/or AN usi ng the equation: BDE(HB)(+) = 1.37pK(HB)(+) + 23.1 E(ox)(B) + C (C equ als 59.5 kcal/mol in AN and 73.3 kcal/mol in DMSO) gave estimates of s olution phase homolytic bond dissociation energies of H-B+ bonds. Gas- phase BDE values of H-B+ bonds were estimated from updated proton affi nities (PA) and adiabatic ionization potentials (aIP) using the equati on, BDE-(HB+)(g) = PA + aIP - 314 kcal/mol. The BDE(HB)(+) values esti mated in AN were found to be 5-11 kcal/mol higher than the correspondi ng gas phase BDE(HB+)(g) values. These bond-strengthening effects in s olution are interpreted as being due to the greater solvation energy o f the HB+ cation than that of the B--. radical cation.