Differential broadening between the signals split by the residual dipolar interaction with 14N in 13C CP/MAS NMR spectra of nitroanilines

The C-13 CP/MAS NMR spectra of various nitroanilines have been measured, and the origin of the differential broadening observed between the signals split by the residual dipolar interaction with N-14 has been clarified experimentally. The dipolar interaction between H-1 and N-14 is responsible for the C-13 differential broadening, while the direct dipolar interaction with H-1 is neglected. A molecular motion can eliminate the differential broadening, which is presumably the 180 degrees flip of the NH2 group around the C-N axis. Therefore, the differential broadening is highly correlated to the molecular motion and the hydrogen bonding. (C) 1999 Elsevier Science B.V. All rights reserved.