The 1:1 and 2:1 complexes of trigonelline (TRG) with HBr, HI, HNO3, HClO4 and HBF4 have been synthesized and their FTIR, 1H and 13C NMR spectra were analyzed. The 1:1 complexes are divided into two groups. The first group includes complexes with HBr,HI andHNO3, in which a proton is transferred from the acid to TRG and the anions are bonded with the carboxylic group, COOHźźźX- (1). The second comprises complexes with HClO4 and HBF4, with two molecules of protonated TRG forming dimer, like benzoic acid, and the anions interacting exclusively with the positively charged nitrogen atoms (2). All 2:1 complexes crystallized with one water molecule and their FTIR spectra are of Had4i type iii, characterized by an intense broad (continuum) absorption below 1600 cm-1 typical of a short-strong hydrogen bond (SSHB) with a delocalized proton and a single _C=O band. In these complexes the water molecule interacts electrostatically with one positively charged nitrogen atom and the anions with the second one (3). The water molecule additionally forms a hydrogen bond with Br, I and NO3 ions. The proton and carbon chemical shifts of the complexes in D2O have been determined and discussed.
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