HOMOLYTIC SE-H BOND-ENERGY AND IONIZATION-ENERGY OF BENZENESELENOL AND THE ACIDITY OF THE CORRESPONDING RADICAL-CATION

The homolytic Se-H bond energy of benzeneselenol, a very efficient rad ical trap in solution and in the gas phase, was determined experimenta lly by using two independent approaches in a Fourier-transform ion cyc lotron resonance mass spectrometer. The hydrogen-selenium bond strengt h was concluded to be 76-80 kcal mol(-1) based on the measurement of t he efficiency of hydrogen atom abstraction from benzeneselenol by seve ral radical cations. The Se-H bond energy was also determined indirect ly through the use of a thermochemical cycle. This approach required t he measurement of the adiabatic ionization energy of benzeneselenol an d the proton affinity of C6H5Se.. An adiabatic ionization energy of 8. 3 +/- 0.1 eV was obtained by measurement of the efficiencies of variou s electron transfer reactions in the forward and reverse directions. T he proton affinity of C6H5Se. (acidity of the benzeneselenol radical c ation) was found to be 200 +/- 3 kcal mol(-1) based on the measured ef ficiencies of several proton transfer reactions. These two values yiel d a homolytic Se-H bond enthalpy of 78 +/- 4 kcal mol(-1) (at 298 K) f or benzeneselenol. This value is significantly different from the only estimate (67 kcal mol(-1)) currently available in the literature.