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).

Novel Water‐Soluble Poly(m‐benzamide)s: Precision Synthesis and Thermosensitivity in Aqueous Solution

“…Phenyl 4-(methylamino)benzoate 2 [11] and 2-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}ethyl p-toluenesulfonate 4 [12] were prepared according to the literature. A solution of 1.0 M lithium hexamethyldisilazide (LiHMDS) in THF (Aldrich) and dehydrated THF (dry THF; Kanto) as a solvent were used as received without purification.…”

13C NMR chemical shifts of carbonyl groups in substituted benzaldehydes and acetophenones: substituent chemical shift increments

“…1). 9,16,17 Reverse -polarization has also been observed for a variety of benzoic acid derivatives such as methyl benzoates, 6,7 phenylbenzoates, 8 Tables 1 and 2 were applied to the prediction of the carbonyl carbon chemical shift of di-and trisubstituted benzaldehydes and acetophenones in an analogous manner. Calculated chemical shifts for substituted benzaldehydes and acetophenones were generated using Eqn (2), where the appropriate SCS values were taken from Tables 1 and 2.…”

Influence of Aprotic Solvents on the Transmission of Anomalous Substituent Effects on 13C NMR Chemical Shifts at the Carboxyl Carbon (δco) in Meta-Substituted Benzoic Acids: A Strong Evidence for π-Polarization Mechanism

“…The attenuation in the magnitude q I while going from meta-to para-isomers is explicable in terms of the longer distance between the substituent and the carboxyl carbon for the para-isomers. The resonance effect from a para-substituent on d co may be contributed by both resonance-induced p-polarization (q R \ 0) and normal direct resonance effect (q R [ 0) [24], while the former (q R \ 0) only contributes to the resonance effect from a meta-substituent on d co , explaining the less negative rather positive values for (q R ) para .…”

“…Considerable progress has been made towards understanding the physical basis of these shifts [8][9][10][11][12][13][14][15][16], their dependences on substituent effects [8,10,12,[16][17][18][19][20][21][22][23][24][25][26][27][28], and their correlations with the substrate reactivity [22,[25][26][27][28]. An interesting finding is the anomalous (reverse) substituent effect on the chemical shift at the a-carbon ðd C a Þ of an unsaturated side chain (containing a C=C, C:C, C=N, C:N, or C=O group) of an aromatic compound: an electron-withdrawing substituent causes an upfield shift at the a-carbon [8,10,12,[16][17][18][19][20][21][22][23][24][25] in contradiction to the expected decrease in the electron population there.…”

“…An interesting finding is the anomalous (reverse) substituent effect on the chemical shift at the a-carbon ðd C a Þ of an unsaturated side chain (containing a C=C, C:C, C=N, C:N, or C=O group) of an aromatic compound: an electron-withdrawing substituent causes an upfield shift at the a-carbon [8,10,12,[16][17][18][19][20][21][22][23][24][25] in contradiction to the expected decrease in the electron population there.…”