13C NMR of substituted aryl carbenium ions: Continuous dependence of the ipso substituent shifts upon the carbenium character. Use of proportionality relationships for the evaluation of substituent–substituent interactions
✍ Scribed by François Membrey; Bernard Ancian; Jean-Pierre Doucet
- Publisher
- John Wiley and Sons
- Year
- 1978
- Tongue
- English
- Weight
- 366 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
Abstract
^13^C substituent shifts in para‐substituted phenyl and 2‐phenylethenyl carbenium ions have been studied within the general model of para‐disubstituted benzenes XC~6~H~4~Y. Large variations are observed for the ipso shifts induced by the Y substituents (Y = NO~2~. … OCH~3~) depending upon the electron demand at the remote carbenium centre. A good representation of these substituent‐substituent interactions is obtained by a treatment derived from ‘proportionality relationships’, where the deviations from strict additivity are factorized into two terms characterizing, respectively, the influence of the fixed X group on the ring and the susceptibility of the incoming Y substituent. Continuity of the ipso shift variations in an extended range is demonstrated, without break‐off between neutral polarized systems or ions as the electronic influence of the fixed X group increases.