π-Electron ring currents and magnetic properties of porphyrin molecules in the MO LCAO SCF method |
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Authors: | Yuri B Vysotsky Valery A Kuzmitsky Konstantin N Solovyov |
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Institution: | (1) Institute of Physicoorganic Chemistry and Coal Chemistry, Academy of Sciences of the Ukrainian SSR, R. Luxemburg Street 70, 340048 Donetsk, USSR;(2) Institute of Physics, Academy of Sciences of the Byelorussian SSR, Leninsky Prospekt 70, 220072 Minsk, USSR |
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Abstract: | The coupled variant of double-parameter perturbation theory in the MO LCAO SCF method in the London approximation has been
used for the calculation of π-electron current distributions in the molecules of porphin and its derivatives. The chemical
shifts of1H-NMR have been computed on the basis of calculations of ring currents and charge distributions. It is shown that π-electron
ring currents are responsible for the dominant contribution to the shielding of protons. The theoretical and experimental
values of proton chemical shifts are in a good agreement. Chemical shifts of the13C and15N nuclei have also been estimated. Two aromaticity scales are proposed for the compounds under study based on the calculations
of the π-electron contribution to the diamagnetic susceptibility and of π-electron currents, respectively. |
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Keywords: | Porphyrins Ring currents Chemical shifts Diamagnetic shielding |
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