Nuclear Magnetic Resonance Spectra of Benzoxadiazole, Benzothiadiazole, Benzoselenadiazole and Quinoxaline

概要

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The NMR spectra of the benzenoid ring protons in benzoxadiazole, benzothiadiazole, benzoselenadiazole and quinoxaline have been analyzed as AA'BB' spin systems by an iterative method. The theoretical spectra showed good agreements with the experimental spectra in line frequencies and their relative intensities. The obtained chemical shifts and coupling constants exhibit some interesting features corresponding to the molecular structural changes arised from the replacement of oxygen by sulfur, selenium and carbon double bond. The chemical shift ν_Oδ_<AB> was found to decrease with the more delocalized π-electron distribution and to suggest a d-orbital model for sulfur. The relative magnitudes of the two ortho-coupling constants and their variations from molecule to molecule were tentatively correlated with the changes of the internal bond angles in the benzenoid ring. The relation of J_<para>>J_<meta> in benzoxadiazole was interpreted in terms of a negative contribution of π-electrons to J_<meta>.
公益社団法人日本薬学会の論文
1969-09-25