title: On the applicability of resonance forms in pyrimidinic bases. II. QTAIM interpretation of the sequence of protonation affinities.
abstract: 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).
authors.affiliation: Departamento Química Organica and Departamento Química Física, Universidade de Vigo, Lagoas-Marcosende, 36200-Vigo, Galicia, Spain.
authors.forename: María J
authors.initials: MJ
authors.lastname: Gonzalez Moa
authors.forename: Ricardo A
authors.initials: RA
authors.lastname: Mosquera
mesh_terms: 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*
chemical_list: D000596:Amino Acids; D010455:Peptides; D011522:Protons; D011743:Pyrimidines; D014498:Uracil; D009584:Nitrogen