title: Evidence of substituent-induced electronic interplay. Effect of the remote aromatic ring substituent of phenyl benzoates on the sensitivity of the carbonyl unit to electronic effects of phenyl or benzoyl ring substituents.
abstract: Carbonyl carbon (13)C NMR chemical shifts delta(C)(C[double bond]O) measured in this work for a wide set of substituted phenyl benzoates p-Y-C(6)H(4)CO(2)C(6)H(4)-p-X (X = NO(2), CN, Cl, Br, H, Me, or MeO; Y = NO(2), Cl, H, Me, MeO, or NMe(2) ) have been used as a tool to study substituent effects on the carbonyl unit. The goal of the work was to study the cross-interaction between X and Y in that respect. Both the phenyl substituents X and the benzoyl substituents Y have a reverse effect on delta(C)(C[double bond]O). Electron-withdrawing substituents cause shielding while electron-donating ones have an opposite influence, with both inductive and resonance effects being significant. The presence of cross-interaction between X and Y could be clearly verified. Electronic effects of the remote aromatic ring substituents systematically modify the sensitivity of the C[double bond]O group to the electronic effects of the phenyl or benzoyl ring substituents. Electron-withdrawing substituents in one ring decrease the sensitivity of delta(C)(C[double bond]O) to the substitution of another ring, while electron-donating substituents inversely affect the sensitivity. It is suggested that the results can be explained by substituent-sensitive balance of the contributions of different resonance structures (electron delocalization, Scheme 1).
authors.affiliation: Department of Chemistry, University of Turku, FIN-20014 Turku, Finland. helmi.neuvonen@utu.fi
authors.forename: Helmi
authors.initials: H
authors.lastname: Neuvonen
authors.forename: Kari
authors.initials: K
authors.lastname: Neuvonen
authors.forename: Paavo
authors.initials: P
authors.lastname: Pasanen