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Study of the effect of N ‐protonation and N ‐methylation on the 1 H and 13 C chemical shifts of the six‐membered ring in benzazoles and 2‐substituted N,N ‐dimethylamino derivatives
Author(s) -
Benassi Rois,
Grandi Romano,
Pagi Ugo M.,
Taddei Ferdinando
Publication year - 1986
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/mrc.1260240505
Subject(s) - chemistry , protonation , benzoxazole , benzothiazole , chemical shift , ring (chemistry) , molecule , substituent , medicinal chemistry , benzimidazole , stereochemistry , organic chemistry , ion
The 1 H and 13 C NMR spectral data of benzimidazole, benzoxazole, benzothiazole and N ‐methylbenzimida‐zole and of their 2‐ N,N ‐dimethylamino derivatives are reported. The spectra were recorded in acetone‐water solution. The chemical shifts of these molecules are compared with those of the corresponding cations obtained by N ‐protonation and N ‐methylation of the neutral molecules. The carbon atoms C‐4, C‐5, C‐6 and C‐4a show a qualitatively identical behaviour, moving to higher field when the cations are formed from the benzazoles examined, but a different behaviour is found for C‐2, C‐7 and C‐7a, which depends on the heterocyclic ring, on the presence of the substituent in position 2 and on the type of cation formed ( N ‐protonation and N ‐methylation cause different effects). The conversion of benzazoles into the corresponding cations causes all 1 H chemical shifts to move to lower field.