Are ring currents still useful to rationalize the benzene proton magnetic shielding?
[structure: see text] The conventional interpretation of proton NMR chemical shifts is supported by large basis set ab initio quantum mechanical calculations. The benzene protons are predicted to lie within the deshielding zone defined in terms of the out-of-plane magnetic shielding domain. However, ring currents by themselves are not sufficient to account quantitatively for the observed benzene proton downfield chemical shift. sigma-Electron contributions must also be taken into account. The conventional explanation for the ethyne proton chemical shift is valid.
Viglione
Rosario G
RG
Dipartimento di Chimica, Universitá degli Studi di Salerno, via S. Allende, 84081 Baronissi SA, Italy.
Zanasi
Riccardo
R
Lazzeretti
Paolo
P