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Formation and mechanism for reactions of ring‐substituted phenonium ions in aqueous solution
Author(s) -
Tsuji Yutaka,
Richard John P.
Publication year - 2016
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.3510
Subject(s) - carbocation , chemistry , nucleophile , reactivity (psychology) , aqueous solution , ring (chemistry) , selectivity , leaving group , diene , ion , computational chemistry , medicinal chemistry , photochemistry , organic chemistry , catalysis , medicine , natural rubber , alternative medicine , pathology
The results of studies on the structure and reactivity of spiro[5.2]oct‐5,7‐diene‐4yl carbocation [phenonium ion] have had a significant impact on the course of discussion about the distinction between classical and nonclassical carbocations. This minireview will present a brief overview of the structure, bonding, and reactivity of ring‐substituted phenonium ions (X‐4 + ), with an emphasis on work completed since 2004. The discussion will focus on the development of new experimental protocol for determination of the selectivity for addition of nucleophilic anions to X‐4 + in aqueous solution. The existing relationships between carbocation lifetime and nucleophilic selectivity, and the known lifetime of ca 140 s for spiro[2.5]oct‐4,7‐diene‐6‐one provide rough estimates of the lifetimes for 4‐Me‐4 + and 4‐MeO‐4 + in aqueous solution. Evidence is presented that nucleophile addition to X‐4 + proceeds through an “exploded” transition state, with relatively weak bonding of the nucleophile and leaving group, and the development of significant positive charge at the reacting primary cyclopropyl carbon. Copyright © 2015 John Wiley & Sons, Ltd.