1,721,168 research outputs found
Semi-empirical calculations of the magnetic properties of condensed hydrocarbons
No full textThe uncoupled Hartree-Fock perturbation method has been used to evaluate the contribution of ring currents to proton shielding constants, magnetic susceptibilities and anisotropies of large condensed hydrocarbons. Good agreement was found between experimental and calculated values. A comparison with HMO and ASMO methods is reported and the ring-current model is discussed
Uncoupled Hartree-Fock calculation of ring currents in substituted benzenes
No full textUncoupled Hartree-Fock perturbation theory has been used to calculate magnetic properties in substituted benzene
Uncoupled and Coupled Hartree-Fock Calculations of Dipole Polarizabilities of Condensed Hydrocarbons
No full textUncoupled and coupled Hartree–Fock perturbation theories are employed to calculate the electric dipole polarizabilities of condensed hydrocarbons in the framework of the Pariser–Parr–Pople approximation. An empirical way of taking into account -effects is studied. Agreement between calculated and experimental results is remarkably good
Further comments on ring currents in five-membered heterocyclic molecules
No full textFURTHER COMMENT
Charge density and NMR parameters. Aliphatic derivatives
No full textThe charge distribution in several substituted aliphatic derivatives was determined by a parametric MOLCAO method. The charges were successfully employed to interpret NMR parameters, namely proton and carbon chemical shift and vicinal proton-proton coupling constants in ethyl derivatives and carbon-proton coupling constants.The linear correlations found between NMR parameters and charge densities are restricted to substituents of the same row of the periodic system. The decay along the aliphatic chain of the perturbation induced by substituents on proton chemical shift is also reproduced by charge distribution. Some results also seem to indicate that the substituents affect the hybridization of the attached carbon atom
An interpretation of 1H and 13C chemical shifts in substituted benzenes on the basis of M.O. charge densities
No full textThe results of an MOLCAO calculation on both and electron systems of several substituted benzenes are reported. The charge densities obtained reproduce the dipole moments of the molecules examined, provided that substituents with strong mesomeric effects are not present. It is shown that there is a satisfactory agreement between 13C and 1H chemical shifts and the trend of total charge densities for all positions of substituted benzenes
The intermolecular electrostatic and magnetic effects of the carbonyl group on the shielding constant of proton
No full textThe intermolecular effects of a carbonyl group on the shielding constant of proton are analysed. An experimental evaluation of the contribution to chemical shift is suggested on the basis of bond distances for hydrogen bonding determined by CNDO/2. The reliability of the McConnell and Musher-Buckingham equations is tested and discussed
Proton chemical shift and localization in aliphatic open-chain hydrocarbons
No full textA relationship between proton chemical shift and hybridization at carbon has been established in open-chain alkanes, suggesting that, in these compounds, proton shielding depends miainly on C–H bond electrons
Magnetic criteria for aromaticity
No full textThe coupled Hartree-Fock perturbation theory is used within the framework of the Pariser-Parr-Popleapproximation to compute the magnetic susceptibility, NMR shielding constants, and electric dipole polarizabilityof aromatic molecules. It is shown that the contribution to the magnetic susceptibility Componentperpendicular to the molecular plane serves as a more reliable aromaticity index than that based on magneticanisotropy or NMR data
Orbital hybridization and proton chemical shifts in substituted methanes
No full textA CORRELATION BETWEEN ORBITAL HYBRIDIZATION AND CHEMICAL SHIFT IN SUBSTITUTED METHANES HAS BEEN REPORTE
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