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Die nucleofuge Aktivität von Substituenten am Brückenkopf von Bicyclo[2.2.2]octan und Chinuclidin Das k OTs / k Br ‐Verhältnis als mechanistisches Kriterium. Fragmentierungsreaktionen, 24. Mitteilung
Author(s) -
Grob C. A.,
Kostka K.,
Kuhnen F.
Publication year - 1970
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19700530318
Subject(s) - chemistry , solvolysis , bicyclic molecule , octane , nucleophile , medicinal chemistry , bromide , hydrogen bromide , nucleophilic substitution , stereochemistry , bromine , organic chemistry , hydrolysis , catalysis
The rate ratios k OTs / k Br of the bridgehead tosylate and bromide of bicyclo [2.2.2]‐octane and quinuclidine, respectively, have been determined in 80 vol.‐% ethanol. The high ratio for the bicyclo [2.2.2] octane derivatives (3,3 · 10 3 at 25°) indicates a highly ionic transition state. Since nucleophilic assistance to ionisation by solvent is precluded in this system a ratio of 10 3 or greater is typical for the «limiting» S N 1 mechanism. Lower k OTs / k Br ratios therefore reflect increasing nucleophilic participation in the transition state of substitution and elimination reactions. The high k OTs / k Br ratio for 4‐substituted quinuclidines, namely 1,6 · 10 3 at 25°, indicates the absence of anchimeric nitrogen participation in the transition state of this synchronous fragmentation. The rates of the 4‐haloquinuclidines follow the normal order of nucleofugal activity for halides in solvolysis reactions.