Comment on "Intrinsic convergence in close-shell SCF calculations. A general criterion"

Fil:Facelli, J.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Contreras, R.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

A general relation between the intrinsic convergence properties of SCF Hartree-Fock calculations and the stability conditions of their solutions

In this paper, the convergence criteria given by Stanton [J. Chem. Phys. 75, 5416 (1981)] for the Hartree-Fock SCF calculations of closed-shell systems are generalized for an unrestricted one-determinantal Hartree-Fock SCF calculation. Finally, these criteria are related to the stability conditions of the Hartree-Fock wave functions. © 1983 American Institute of Physics.Fil:Facelli, J.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Contreras, R.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Ab initio and 17O NMR study of aromatic compounds with dicoordinate oxygen atoms. 2. Intramolecular hydrogen bonding in hydroxy- and methoxybenzene derivatives

The 17O chemical shifts of several ortho-substituted phenols and anisoles are presented along with those of the corresponding para-substituted compounds. The measurements of the various ortho-para pairs were done in the same solvent and at the same temperature in order to experimentally estimate the effect of intramolecular hydrogen bonding on the 17O chemical shielding in the ortho compounds by using the ortho-para equivalence rule. Ab initio calculations of the 17O chemical shieldings reproduce well the experimental findings and provide a theoretical description of the hydrogen-bonding effect on the 17O chemical shifts. © 1991 American Chemical Society.Fil:Biekofsky, R.R. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Pomilio, A.B. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Contreras, R.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Facelli, J.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Ab initio and 17O NMR studies of the substituent effects on the tautomeric equilibrium in 6-X-1H-2-pyridones

17O chemical shifts are found to be highly sensitive probes in the study of keto-enol tautomeric equilibria due to the strong sensitivity of these shifts to the coordination of the oxygen atom. The large shielding effect observed, both experimentally and theoretically, for the carbonyl oxygen atom in 2-pyridone suggests that the carbonyl π-electronic system is undergoing a strong conjugation with the formal C3=C4 double bond and/or the nitrogen lone pair. A Cl or NH2 substitution at position 6 of the pyridine ring shifts the tautomeric equilibrium toward the 2-hydroxypyridine form, while a CH3 substitution results in the keto form being predominant, as is the case in the parent compound. © 1992 American Chemical Society.Fil:Facelli, J.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Contreras, R.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Tufró, M.F. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Comment on "Intrinsic convergence in close-shell SCF calculations. A general criterion"

Fil:Facelli, J.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Contreras, R.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

A general relation between the intrinsic convergence properties of SCF Hartree-Fock calculations and the stability conditions of their solutions

In this paper, the convergence criteria given by Stanton [J. Chem. Phys. 75, 5416 (1981)] for the Hartree-Fock SCF calculations of closed-shell systems are generalized for an unrestricted one-determinantal Hartree-Fock SCF calculation. Finally, these criteria are related to the stability conditions of the Hartree-Fock wave functions. © 1983 American Institute of Physics.Fil:Facelli, J.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Contreras, R.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Ab initio and 17O NMR study of aromatic compounds with dicoordinate oxygen atoms. 2. Intramolecular hydrogen bonding in hydroxy- and methoxybenzene derivatives

The 17O chemical shifts of several ortho-substituted phenols and anisoles are presented along with those of the corresponding para-substituted compounds. The measurements of the various ortho-para pairs were done in the same solvent and at the same temperature in order to experimentally estimate the effect of intramolecular hydrogen bonding on the 17O chemical shielding in the ortho compounds by using the ortho-para equivalence rule. Ab initio calculations of the 17O chemical shieldings reproduce well the experimental findings and provide a theoretical description of the hydrogen-bonding effect on the 17O chemical shifts. © 1991 American Chemical Society.Fil:Biekofsky, R.R. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Pomilio, A.B. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Contreras, R.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Facelli, J.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Effects of electronic resonance interaction on the methoxy group NMR parameters. Theoretical and experimental study of substituted 2-methoxypyridines

In order to increase the understanding of the interactions which define the planar conformation of the methoxy group with respect to the aryl ring in methyl aryl ethers and the effect these interactions have on the methoxy NMR parameters, 17O and 13C spectra were measured and ab initio optimized geometries were calculated for three different conformations of the methoxy group in 2-methoxy-5-X-pyridines (X = H, NO2, and NH2). 17O and 13C chemical shifts were also calculated using the LORG approach. It was found that, contrary to what has been commonly assumed, the oxygen and the carbon of the methoxy group are deshielded when the electronic resonance interaction is increased. Therefore, the large 13C deshielding effect observed for a conformation with an out-of-plane methoxy group in aryl methyl ethers and related compounds has to be attributed to the inhibition of the attractive van der Waals forces between the methyl moiety and the aromatic ortho-cis carbon atom. © 1993 American Chemical Society.Fil:Contreras, R.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Biekofsky, R.R. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Facelli, J.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina