RADICALS AND IONS OF GLYCINE - AN AB-INITIO STUDY OF THE STRUCTURES AND GAS-PHASE THERMOCHEMISTRY

The structures of glycine and the related radicals and ions were optim ized at both HF/6-31G(D) and NP2/6-31G(D) levels. The vibrational freq uencies were calculated at the HF/6-31G(D) or MP2/6-31G(D) levels and the total energies of these molecules were evaluated at the G2(MP2) le vel. Proton affinities (PAs) and bond dissociation energies (BDEs) wer e found. The PAs and BDEs demonstrate that there is a strong captodati ve stabilizing effect for the C-centered radicals. Thus for H2NCH2COOH the C-H BDE is relatively low, 331 kJ mol(-1). Using the G2(MP2) ener gies, the glycine ionization potential (894 kJ mol(-1)) and the acylox yl radical electron affinity (358 kJ mol(-1)) were also derived. Value s of C-p(o), S-o, H-o - H-0(o), Delta(i)H(o); and Delta(f)G(o) at 298 K were calculated. The recommended values of Delta(f)H(298)(o) (in kJ mol(-1)) are as follows: H3NCH2COOH+ (249), H3NCHCOOH.+ (454), H-2-NCH 2COOH.+ (502), H3NCH2COO.+ (547), H2NCH2(OH)(2)(.+) (399), H2NCH2COOH (-392), H2NCHCOOH. (-279), HNCH2COOH. (-181), H2NCH2COO. (-138), H2NCH 2COO- (-491), H2NCHCOO.(-) (-346), and HNCH2COO.- (-303).