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Differential broadening caused by dipolar interaction with 1 H in 13 C MAS NMR signals split by residual dipolar interaction with 14 N
Author(s) -
Hayashi Shigenobu
Publication year - 1999
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/(sici)1097-458x(199911)37:11<843::aid-mrc548>3.0.co;2-7
Subject(s) - chemistry , residual dipolar coupling , dipole , crystallography , carbon 13 nmr , differential (mechanical device) , hydrogen bond , amide , molecule , stereochemistry , organic chemistry , physics , thermodynamics
The 13 C cross‐polarization magic angle spinning NMR spectra of various nitroanilines and some other N‐containing compounds were measured and the differential broadening between the signals split by the residual dipolar interaction with 14 N was investigated. The dipolar interaction between 14 N and 1 H produces 13 C differential broadening as well as the 13 C– 14 N interaction does, whereas the dipolar interaction between 13 C and 1 H is discounted as its origin. The differential broadening caused by 1 H is observed in the C*—NHR (R = H and CH 3 ) groups at the para and ortho positions to the NO 2 group in nitroanilines, C—NH 2 in m ‐nitroaniline and 13 C bonded to the amide NH group, where 14 N is directly bonded to 1 H and molecular motions are restricted by hydrogen bondings. At higher temperatures the differential broadening decreases in the para ‐type nitroanilines. The 1 H‐caused differential broadening is not observed for the C—NH 2 group in the meta ‐type nitroanilines except for m ‐nitroaniline, C—NO 2 , C*—N(CH 3 ) 2 and C—NH 3 groups. Molecular motions can reduce the differential broadening, which are presumably the 180° flip of the NH 2 group and the rotation of the NH 3 group around the C—N axis. Copyright © 1999 John Wiley & Sons, Ltd.