Structure,stability, and disproportionation mechanisms of organic interhalides of the cholinium series: an experimental and theoretical study

The stability constants of acetylcholinium, carbamoylcholinium, and cholinium diiodochlorides and diiodobromides in chloroform solutions were determined and the kinetics of disproportionation of these systems in 1 : 9 CHCl₃—MeOH (MeCN) mixtures were studied by UV spectroscopy. A possible mechanism of mutual transformations of the polyhalides is proposed and an interrelation between the nature of the iodine-coordinating solvent and the extent of reversibility of the process is established. The electronic structures and relative stabilities of acetylcholinium iodohalides and charge-transfer complexes S·XI₂ ^– and S·I₂ (S = MeOH, MeCN, CHCl₃; X = Cl, Br, I) were studied by ab initio RHF and MP2(full) methods in the HW+(3d) and 6-31G++(d,p) basis sets. It was found that all the solvents studied favor the decomposition of the iodohalide anions to liberate molecular iodine; however, disproportionation of I₂ is possible only for the S·I₂ complexes with a high extent of charge transfer.