Nucleophilicity and Basicity in the Quaternization of 4‐Substituted Quinuclidines. Polar effects. Part III

Publisher Website
Google Scholar
Abstract
The second order rate constants (k) for quaternization of thirty 4‐substituted quinuclidines (1) by methyl iodide in methanol have been measured. The effects of the substituents on rate are relatively small and indicate an early transition state with little charge separation. They also indicate less involvement of the nitrogen atom,i.e.a looser transition state, for quaternization by allyl halides than for the less reactive propyl halides. The logkvalues of 4‐substituted quinuclidines correlate moderately well with their pKavalues, the main reason being the imperfect correlation between nucleophilicity and basicity. The assumption that substituents exert equal effects on rates and equilibria is therefore only partly justified. Certain irregularities in the correlation can be attributed to a reduction of the nucleophilicity of nitrogen in1due to hydrogen bonding to the solvent methanol. Furthermore, quaternization is faster and responds more strongly to substituent effects in the aprotic solvent acetonitrile.

This publication has 13 references indexed in Scilit: