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13 C NMR spectra of para ‐substituted methoxybenzenes and phenols in the solid state: Examination of chemical shift non‐equivalence in ortho and meta carbons related to non‐equivalent electron distribution, and application to assignment of peaks in meso ‐hexestrol and its derivatives
Author(s) -
Saitǒ Hazime,
Yokoi Motoko,
Aida Misako,
Kodama Masahiko,
Oda Taiko,
Sato Yoshihiro
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.1260260212
Subject(s) - chemistry , substituent , steric effects , nmr spectra database , chemical shift , crystallography , spectral line , ether , carbon 13 nmr , molecule , phenols , stereochemistry , organic chemistry , physics , astronomy
13 C NMR spectra of para ‐substituted methoxybenzenes and phenols were recorded in the solid state to gain an insight into the manner and origin of substantial peak splittings in the ortho (up to 9.2 ppm) and meta (up to 2.5 ppm) carbon signals. It was difficult to account for these peak splittings only by the steric interaction with the methyl group of the substituent, because their magnitude varied widely from 4.6 to 9.2 ppm with a variety of substituents at the para position, and the meta carbon peaks are also split into doublets. Instead, it was found that the electron density non‐equivalence between the two ortho and the two meta carbons is mainly responsible for the splittings, as manifested by the presence of an approximate linear relationship between the displcements of the 13 C NMR peaks and total electron density. The observed additional splitting in the 13 C NMR spectra of meso ‐hexestrol and its methyl or ethyl ether(s) in the solid state was similarly explained. Stereochemical features of these molecules in the solid state are discussed on the basis of the 13 C NMR data.