Effects of changes in conformation and configuration of N-containing compounds on NMR spactra

AimTo find the cause of abnormal NMR spectra of lomerizine dihydrochloride, cetirizine dihydrochloride and flenfluramine camphoramide. MethodsHypothesizing, in given conditions, there are changes of stereoisomeric conformation and configuration in structure of N-containing compounds, it resuts in abnormality of NMR spectra. By using the method of NMR, it is confirmed credibily. Results and Conclusion The moving balance exists between two chair conformations in lomerizine dihydrochloride and cetirizine dihydrochloride. It causes that spin-nuclei of whole molecule are placed in two chemical circumstance. In solution of DMSO-d6, the speed of conformation reversal equals to the NMR time scale, so that chemical shift of spin-nuclei can not be definitely determined, peaks are broadened and even collapsed. After dropping D₂O or increasing the temperature, the viscosity of the solution is decreased, the speed of reversal is quicker than NMR time scale, then normal spectra are obtained. Owing to the reversal of the three bonds of nitrogen in flenfluramine camphoramide is limited, other pair of diastereoisomer resulted from the asymmetric nitrogen can be detected by NMR. Multiplication of the peaks of 13CNMR is reasonably explained.