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Stereochemistry of hexakis (3‐methoxyphenyl) benzene and hexakis(3‐methylphenyl) benzene. An incremental chemical shift model for meta ‐substituted hexaphenylbenzenes
Author(s) -
Pepermans Henri,
Willem Rudolph,
Gielen Marcel,
Hoogzand Cornelis
Publication year - 1988
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260260408
Subject(s) - chemistry , benzene , conformational isomerism , chemical shift , aryl , stereochemistry , nmr spectra database , proton nmr , absorption spectroscopy , spectral line , crystallography , computational chemistry , medicinal chemistry , molecule , organic chemistry , alkyl , physics , quantum mechanics , astronomy
Abstract The 1 H 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.