The influence of common cation BH+ on the products of reactions between C-acids and strong guanidine bases in acetonitrile solvent

Abstract

The electronic spectra of the products of reactions between C-acids (4-nitrophenylcyanoalkanes, 4-nitrophenylnitroalkanes and trinitrotoluene) and 1,1,3,3-tetramethylguanidine (TMG), pentamethylguanidine (PMG) and MTBD bases (B) have been recorded in B/BH⁺ buffers in acetonitrile at 25 °C. Large BH⁺ concentrations had little or no effect on the spectra of the nitrile or trinitrotoluene anions, while the spectra of nitroalkane anions were shifted to the blue by some 50–75 nm. These shifts were ascribed to the formation of hydrogen-bonded ion pairs. In the case of TMG or PMG reactions two types of ion pairs are formed due to homoconjugation of BH⁺ cations, which is why an isosbestic point is not observed, while MTBD reactions are free from such complications. The spectra of some ion pair products and ion pair dissociation constants were calculated.