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Transmission of polar substituent effects through the bicyclo[2.2.2]octane ring system as monitored by NMR shifts: A 13 C NMR study of 4‐substituted‐1‐methylbicyclo[2.2.2]octanes
Author(s) -
Adcock William,
Abeywickrema Anil N.,
Iyer V. Sankar,
Kok Gaik B.
Publication year - 1986
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260240306
Subject(s) - substituent , chemistry , electronegativity , bicyclic molecule , chemical shift , ring (chemistry) , computational chemistry , stereochemistry , organic chemistry
Carbon‐13 substituent chemical shifts (SCS) are reported for the methyl group of a series of 4‐substituted 1‐methylbicyclo[2.2.2]octanes covering a wide range of electronic substituent effects. Unlike the 13 C SCS of the α‐carbon centre in various unsaturated side‐chain probes attached to the bicyclo[2.2.2]octane ring, which are mainly proportional to substituent field effects (σ F ), the 13 CH 3 , SCS are found to display a definitive statistical dependence on substituent electronegativity effects as well as the field parameter. Compelling support for the validity of the statistical dissection by multivariate analysis is provided by an independent measure of polar susceptibility parameters (ρ F ; CDCl 3 , and CCl 4 ). The coefficient ( A ) of the Buckingham equation for linear electric field effects on the CH 3 , group is calculated for CCl 4 as the solvent. The origin of the reverse substituent electronegativity effect is discussed, and compared with the similar phenomenon displayed by the resonance contribution to the 13 C SCS of the β‐carbon of p ‐substituted ethylbenzenes.