DYNAMIC NMR AS A NONDESTRUCTIVE METHOD FOR DETERMINATION OF RATES OF DISSOCIATION .21. DISSOCIATION IN 1-(1-HALOETHYL)PYRROLIUM CATIONS

Topomerization observed for the isopropyl-methyls in the title compoun ds was reinvestigated with use of the total line shape analysis of NMR spectra. It was found that deprotonation from the pyrrolium cation pr eceded and was an independent step from the topomerization but the for mer strongly affects kinetic parameters for the latter process in the presence of excessive hydrogen halide. The extent of the excessiveness of hydrogen halide in the system also affects the reaction rates and the effects were discussed on the standpoint of activation parameters. The rates of topomerization of the isopropyl-methyls were found to be identical with the rates of enantiomerization at the 1-substituent in 1-(1-bromopropyl)-3-isopropyl-2-phenylpyrrolium ion to suggest that t he topomerization in other compounds was also attributed to the ioniza tion at the I-substituent. The results suggest that a 1-pyrrolyl group assists ionization of 1-pyrrolylmethyl halide more effectively than a phenyl group in benzyl halide. This was reproduced by ab initio calcu lations.