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Stereochemistry of hexakis(3-methoxyphenyl)benzene and hexakis(3-methylphenyl)benzene. An incremental chemical shift model for meta-substituted hexaphenylbenzenes

par Pepermans, Henri;Willem, Rudolph ;Gielen, Marcel ;Hoogzand, C.
Référence Magnetic resonance in chemistry, 26, 4, page (311-318)
Publication Publié, 1988-04

Article révisé par les pairs

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Résumé :

The 1H NMR spectrum of hexakis(3-methoxyphenyl)benzene exhibits a methoxy absorption which looks exactly like a triplet. The spacing between the signals is, however, proportional to rather than independent of the field strength. The aryl H-5 region of this compound and the methyl region of hexakis(3-methylphenyl)benzene display similar field-proportional, triplet-like splittings. This property of meta-substituted hexaphenylbenzenes cannot be explained by either preferential or residual isomerism, even in the presence of many accidental isochronies. A chemical shift model based on the hypothesis that the meta substituents do not disturb the geometry of the hexaphenylbenzene skeleton or the populations of the rotamers explains the spectra in a straightforward manner.