THE ELECTRON-AFFINITIES OF THE RADICALS FORMED BY THE LOSS OF AN AROMATIC HYDROGEN-ATOM FROM ADENINE, GUANINE, CYTOSINE, URACIL, AND THYMINE

The major ion formed in Negative Ion Chemical Ionization Mass Spectrom etry of Adenine, Guanine, Cytosine, Uracil and Thymine is the dehydrog enated anion, The CURES EC procedure for optimizing Austin Model-1 Mul ticonfigurational Configuration Interaction semi-empirical calculation s is applied to the electron affinities of the corresponding dehydroge nated bases and N-H bond dissociation energies. These calculated value s will be compared with Literature values of the gas phase acidities o f the purines and pyrimidines. The N-H bond dissociation energies are about 3.95 eV for Guanine, Adenine, and Thymine and 4.08 eV for Cytosi ne and Uracil, The electron affinities of the radicals are A(MinH) = 3 .50 eV, G(MinH) = 3.46 eV, C-MinH = 3.38 eV, U-MinH = 3.48 eV, T-MinH = 3.46 eV. (C) 1998 Academic Press.