13C 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
✍ Scribed by Hazime Saitǒ; Motoko Yokoi; Misako Aida; Masahiko Kodama; Taiko Oda; Yoshihiro Sato
- Publisher
- John Wiley and Sons
- Year
- 1988
- Tongue
- English
- Weight
- 543 KB
- Volume
- 26
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
13C 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 mefa (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 a t 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 displacements of the 13C NMR peaks and total electron density. The observed additional splitting in the 13C NMR spectra of mesohexestrol and its methyl or ethyl ether@) in the solid state was similarly explained. Stereochemical features of these molecules in the solid state are discussed on the basis of the 13C NMR data.