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The effect of unsaturation on the structure and bonding in the unsaturated chromium carbonyl nitrosyls is examined to compare with the isoelectronic homoleptic manganese carbonyl derivatives by using the density functional theory method. It is observed that there are significant shifts in the relative energies of various structural types of metal carbonyl nitrosyls particularly for unsaturated molecules.

The structures, energetic and vibrational frequencies of nine hydrogenated 9H-keto-guanine radicals [(G+H).sup..] and close shell anions [(G+H).sup.-] are predicted using B3LYP density functional method. The results show that the energetic order for the anions differs from that of the analogous radical, the [(G+H).sup..] and [(G+H).sup.-] readily exists as the products of consecutive electron attaching to [(G+H).sup.+].

The structures, energetics, and vibrational frequencies of nine hydrogenated 9H-keto-guanine radicals (GH)•and closed-shell anions (GH)-are predicted using the carefully calibrated (Chem. Rev.2002, 102, 231) B3LYP density functional method in conjunction with a DZP basis set. These radical and anionic species come from consecutive electron attachment to the corresponding protonated (GH)cations in low pH environments. The (GH)cations are studied using the same level of theory. The proton affinity (PA) of guanine computed in this research (228.1 kcal/mol) is within 0.7 kcal/mol of the latest experiment value. The radicals range over 41 kcal/mol in relative energy, with radical r1, in which H is attached at the C8 site of guanine, having the lowest energy. The lowest energy anion is a2, derived by hydride ion attachment at the C2 site of guanine. No stable N2-site hydride should exist in the gas phase. Structure a9was predicted to be dissociative in this research. The theoretical adiabatic electron affinities (AEA), vertical electron affinities, and vertical detachment energies were computed, with AEAs ranging from 0.07 to 3.12 eV for the nine radicals. [ABSTRACT FROM AUTHOR]