E. Alcalde et al., HETEROCYCLIC BETAINES .19. UNCONVENTIONAL EXTENDED PI-SYSTEMS CONTAINING PYRIDINIUM AND BENZIMIDAZOLATE SUBUNITS - SYNTHESIS AND CHARACTERIZATION, Journal of organic chemistry, 59(3), 1994, pp. 639-643
A convenient synthesis and characterization of several examples of (E)
-2- [2-(1-alkyl-3-pyridinio): vinyl] benzimidazolate inner salts and (
E)-1-alkyl-2(or 4)-[2- enzimidazol-2-ylidene)ethylidene]-dihydropyridi
nes with a betaine character is reported. Their structural aspects are
discussed mainly on the basis of the H-1 NMR data and experimental di
pole moment values (11.6-13.0 D). The experimental information availab
le for (E)-1-alkyl-2(or 4)- [2- (benzimidazol-2-ylidene)ethylidene] di
hydrepyridines (A <-> B) is consistent with a betaine character, and t
he dipolar form (B) has been shown to make an important contribution t
o the ground state.