On the applicability of resonance forms in pyrimidinic bases. II. QTAIM interpretation of the sequence of protonation affinities.
The atomic properties of neutral and protonated forms of uracil and some model compounds, computed from B3LYP/6-31++G//B3LYP/6-31G charge densities with the QTAIM theory, indicate that sigma electron reorganization plays a significant role in the protonation processes. This reorganization is substantially different for O=C-C=C and O=C-C-X (X = N, O) units, involving transfers of electron population between all atoms in the first case but not across the C-X bond in the second unit. O-Protonation is basically favored over the N-protonation because of the lower electron population transferred to the proton. The stability sequence of N-protonated forms can be rationalized in terms of the closer position of the proton, when attached to N3, to regions of larger electron population (carbonyl groups).
Gonzalez Moa
María J
MJ
Departamento Química Organica and Departamento Química Física, Universidade de Vigo, Lagoas-Marcosende, 36200-Vigo, Galicia, Spain.
Mosquera
Ricardo A
RA
D000596:Amino Acids / Q000737:chemistry*; D001482:Base Composition; D002627:Chemistry, Physical / Q000379:methods*; D004583:Electrons; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry; D010455:Peptides / Q000737:chemistry*; D011522:Protons; D011743:Pyrimidines / Q000737:chemistry*; D011789:Quantum Theory; D012984:Software; D014498:Uracil / Q000737:chemistry*
D000596:Amino Acids; D010455:Peptides; D011522:Protons; D011743:Pyrimidines; D014498:Uracil; D009584:Nitrogen