Comment on the Relationship between Chemical Shifts and Net Charges
نویسنده
چکیده
where q is the jz net charge (q < 0 for excess electron density) on the adjacent carbon atom. A value of a = 10.7 ppm/electron has been obtained [4] by a re gression analysis between observed shifts and net charges in the diatropic [5] annulenes C5H 5_ , C6H6, C 7H 7+, and C 8H 82~. Herewith it was assumed that RC and L A terms do not differ considerably in these compounds and that the counterion does not affect the shifts. However, later work [6 —8 ] demonstrated that proton shifts of charged annulenes depend sig nificantly on the kind of counterion and so it was concluded [7] that the observed shifts cannot be rationalized by the simple relationship (2 ). In this paper we report on our calculations of 'H chemical shifts of annulenes C5H5~, C6H 6, C7H 7+, C8H 82~, and C 9H9_ according to eq. (1) utilizing the procedure of ref. [ 1 ] which was successfully applied to a considerable number of conjugated hydrocar-
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