N.M.R. and conformational analysis of some Te-containing ortho-substituted benzaldehydes

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Abstract
We report the analysis of the high-resolution proton magnetic resonance spectra of some 2-halotellurenyl-benzaldehydes (Cl, Br, I) and of 2-methyltellurobenzaldehyde, considered as ABCD spin systems. The identification of the long-range couplings in these molecules shows that they all have a ‘cis’ conformation of the aldehyde carbonyl relative to the ortho-substituent. An electronic model which explains this conformation in the case of the haloderivatives is suggested. It agrees with infra-red measurements. In the case of the methylated compound, another model is proposed to account for our observations, in agreement with the results reported by Andrieu and Ruwet for 2-methoxy, 2-methylthio- and 2-methylselenobenzaldehyde. We observed coupling of the methyl protons with the nuclei 123Te (27·0 Hz) and 125Te (32·5 Hz) in 2-methyltellurobenzaldehyde.