17O NMR Spectra of Carbonyl Compounds ArCOX: Influence of Groups X on the Polarity of the Carbonyl Group

Abstract

The 17O shift values of para‐substituted benzoyl compounds p‐YC6H4COX (X=H, CF3, COOEt, Br, Cl, F, SEt, OCOAr, OH, O‐Na+, NH2) were measured. The 17O shielding values δ(17O) of these and other aryl‐unsubstituted benzoyl compounds (Y=H) follow the electron‐donating power of X (resonance), whereas inductive electron attractors (CF3, COOEt) show only small effects. The sensitivity of the shift values to donor/attractor para substituents Y, measured as the Hammett–Taft ρ+=δ(17O)/σ+, follows both the resonance and the inductive effects; combined with the δ(17O) values, it is proposed as an empirical measure of the polarity (electrophilicity) of the carbonyl group (35 types of COX in Table 1).

Influence of ortho substituents on 17O NMR chemical shifts in phenyl esters of substituted benzoic acids

“…Correlation equations obtained in Table 3 could be used to estimate the rates of the alkaline hydrolysis, the carbonyl carbon 13 (25)- (27), Table 3 In relations shown the alkaline hydrolysis is denoted by (AH), the susceptibility to the steric factor by δ S , the carbonyl carbon 13 C chemical shifts by (δ CO ), and the IR carbonyl stretching frequencies by (ν CO ). Using for the alkaline hydrolysis of the phenyl esters of substituted benzoic acids, X- (Table 3) we obtained the values of a 1 = 8.12, a 2 = 7.28 and a 3 = -102.8 which are approximately the same as shown by Eqn (25) ( Table 3).…”

“…[13,14] It was found that in methyl benzoates reaction series an introduction of electron-attracting substituents causes deshielding and electron-donating substituents shielding of the carbonyl and methoxy O atoms. [14][15][16] It has been shown [26][27][28][29] that in substituted carbonyl derivatives, Y-C 6 H 4 CO-X, RCO-X, the shielding of the carbonyl oxygen is increased and the sensitivity of the Y substituent is diminished with an increase in the electron-donating power of the X group.…”

“…The results of correlations of the carbonyl oxygen and the single-bonded oxygen δ( 17 O) values, for phenyl esters of para-, meta-and ortho-substituted benzoic acids, X-C 6 H 4 CO 2 C 6 H 5 , with Eqns (4)-(7) are listed in [27,39,40] X-C 6 H 4 COCl, with Eqns (4)-(6) are shown in Table 2 as well.…”

“…17 O) values for phenyl esters of para-substituted benzoic acids are besides the inductive effect dependent on the through-conjugation between substituent and the carbonyl oxygen similar to that for para-substituted methyl benzoates, [14][15][16] acetophenones, [36,37,59] benzoyl chlorides, [27,39,40] nitrobenzenes. [35,[57][58] The δ(…”

“…[55,56] The calculated sensitivities towards the throughresonance, ρ + , for para-substituted benzoyl chlorides and acetophenones were respectively 21.2, and 24.1 ( Table 2). The corresponding values of ρ + coincide well with the similar ρ + values reported earlier (for benzoyl chlorides ρ + = 21.7, [39] for acetophenones ρ + = 22.5 [27,59] ). For para-substituted nitrobenzenes we obtained ρ + = 14.9 ( Table 2, ρ I = 18.6 [34] and ρ + R = 24.0 [34] ).…”