| Title |
NMR study of heterogeneity in pyridine-N-oxide. . .HCl crystal / |
| Authors |
Balevičius, Vytautas ; Gacesa, Alexandar ; Plavec, Janez |
| DOI |
10.2478/BF02476276 |
| Full Text |
|
| Is Part of |
Central European journal of physics.. Warsaw : Central European Science Journals. 2004, vol. 2, no. 1, p. 120-131.. ISSN 1895-1082 |
| Keywords [eng] |
NMR spectroscopy ; phase transitions ; hydrogen bonding ; pyridine-N-oxide |
| Abstract [eng] |
An origin of narrow H-1 NMR signals in pyridine-N-oxide (PyO)...HCl crystal has been investigated by means of MAS, SPEDAS, NOESY and COSY techniques. Spectra of crystalline samples are compared with those of solid phase obtained from liquid PyO...HCl solutions ( in acetonitile/H2O) after the heterogeneous phase separation. It has been concluded that partially resolved peaks in H-1 NMR spectra of solids are related with heterogeneity of spin system and presence of different H-bond clusters of water molecules. NOESY spectra show no cross-peaks even at very long mixing time (500 ms). This indicates there is no exchange process between spins causing different peaks, and thus the corresponding molecular aggregates are captured in "islands of mobility8 without any channels sufficient for exchange. Appearance of MAS side bands as "pseudo8 cross-peaks in 2D NMR spectra using MAS/COSY technique is reported. In the case of accidental coincidence of spinning frequency (omega(MAS)) with spectral distances between some diagonal signals, intensive non-diagonal peaks are observed at the corresponding cross-positions. A misleading conclusion concerning spin coupling is easy to avoid using various omega(MAS). |
| Published |
Warsaw : Central European Science Journals |
| Type |
Journal article |
| Language |
English |
| Publication date |
2004 |
| CC license |
|
