Differential broadening caused by dipolar interaction with 1H in 13C MAS NMR signals split by residual dipolar interaction with 14N

✍ Scribed by Shigenobu Hayashi

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 133 KB
• Volume: 37
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/(sici)1097-458x(199911)37:11<843::aid-mrc548>3.0.co;2-7

✦ Synopsis

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 Ł -NHR (R D 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 Ł -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.