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

✍ Scribed by Cyril A. Grob; Markus G. Schlageter

Publisher
John Wiley and Sons
Year
1977
Tongue
German
Weight
365 KB
Volume
60
Category
Article
ISSN
0018-019X

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✦ Synopsis

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 log k values of 4‐substituted quinuclidines correlate moderately well with their p__K__~a~ values, 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 in 1 due to hydrogen bonding to the solvent methanol. Furthermore, quaternization is faster and responds more strongly to substituent effects in the aprotic solvent acetonitrile.

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