On the interaction of nitrate with carbenium ions

Abstract

In the course of our studies of the influence of counter ions on the propagation mechanism of cationic vinyl polymerization' -4) we discussed the role of nucleophilic counter ions in transfer suppressed propagations).Counter ions containing oxygen are most important in pseudocationic polymeri-zation6s7) due to their ability to form esters. It was found by theoretical investiga-tions8) and also by experiment9) that the tendency for ester formation of the widely investigated trifluoroacetate ion is comparable with those of the nitrate anion in solution. The role of the nitrate counter ion in cationic vinyl polymerization has been treated very littlelo). Thus, we calculated the interaction between cationic chain end and counter ion using the model system GH: /NO; (Scheme I ) with the help of MIND013 calculations, taking the influence of the solvent into consideration. Scheme I: H2C=CH2 + HNOB Proton transfer Ester formation / \ C,H,@INO,~ -C~H,-O--NO, C2H,0e + NO,@ Oxygen transfer Competition reactions of the ester formation are proton transfer to the counter ion (Eq. (1)) and oxygen transfer to the cation ( Eq. (3)). The hint to competition reaction (3) was received by means of MIND0/3 calculations, using partial optimization of geometry with constant distance of the Co -N-bond.The reaction enthalpies, AH, , according to Scheme 1, for the reactions in the gas phase and in two solvents (methylene chloride and water), are presented in Tab. 1.In the gas phase the ester formation is favoured. The final ionic products formed in reaction (3) are preferred if the polarity of the solvent increases. On the other hand, the ester formation proceeds with strong endothermic effect in the more polar solvent *) Revised manuscript of June 9, 1987.