Correlation analysis of the13C chemical shifts of substituted benzaldehyde 2-aminobenzoylhydrazones. Study of the propagation of substituent effects along a heteroatomic chain

Abstract

The 13C chemical shifts of eight series of para‐ or meta‐substituted benzaldehyde 2‐aminobenzoylhydrazones possessing both amide and imine functionalities were measured. The 13C chemical shifts were used to study the transmission of electronic substituent effects along the heteroaromatic side‐chain of the substituted aromatic ring. In addition to the CN bond, the benzoylhydrazones possess in their side‐chain polarizable CO and phenyl π‐units. The benzylidenic ring‐substituent chemical shifts were analysed by the dual substituent parameter approach to separate the inductive and resonance effects. The negative ρI and ρR values observed (i.e. reverse substituent effects) indicate a significant π‐polarization of the CN bond. The highly negative ρR values, especially those in the case of meta substitution, suggest a contribution from a marked secondary field‐transmitted resonance effect. The results are compared with those obtained for other hydrazones or imines. Variation of the electron‐withdrawing ability of the N2 substituent is seen to have a systematic effect on the ρI values. Reverse substituent effects are also observed at the C‐1″ site of the 2‐aminobenzoyl ring while C‐4″ shifts show normal behaviour, consistent with the general concept of the π‐polarization that each π‐unit of the side‐chain is polarized largely as a localized system. Accordingly, the π‐polarization effect is seen efficiently to propagate also along a heteroaromatic chain. On the other hand, the CO sites exhibit normal, although fairly slight, dependence on the benzylidenic substituent indicating an insignificant role of π‐polarization at that site. The effects of the solvent, CDCl3 vs. DMSO‐d6, on the ρI and ρR values are also considered. © 1997 John Wiley & Sons, Ltd.

Crystal structure, 1H and 13C NMR spectral studies of 1,2,4,5-oxadiazaborole derivatives

“…The good fits with positive ρ values were obtained (Table 7). This shows that the changes in the electron density at C=N carbons and N-H protons are normal and not reverse [31][32][33][34][35]. This means that the substituent dipoles can not polarize π-units (as localized systems) through the space, because of the long distance.…”

Study of the Substituent‐Influenced Anomeric Effect in the Ring‐Chain Tautomerism of 1‐Alkyl‐3‐aryl‐naphth[1,2‐e][1,3]oxazines

“…The changes in the 13 C NMR chemical shift values that are induced by phenyl substituents (SCS) on C2 have been analyzed by various dual substituent parameter approaches. [24][25][26] The best correlation was obtained with the equation SCS = ρ F σ F + ρ R σ R , where σ F characterizes the inductive effect, and σ R the resonance effect, of the aryl substituent. In a previous study on the ring-chain tautomerism of 1,3-diaryl-2,3-dihydro-1H-naphth[1,2-e] [1,3]oxazines, by means of a dual substituent parameter treatment of SCS, the difference in the stabilities of ring forms B and C was explained by the changes in the sp 2 and sp 3 hybridized character of the carbon atom, which is influenced by the aryl substituents on C1 and C3.…”

“…The reverse trend in the inductive substituent effect (σ F ) for unsaturated carbon is well-documented. [25][26][27][28][29][30] The negative slope of σ F for saturated carbon centers such as those situated between the two heteroatoms in 1,3-O,N-heterocycles was explained by Neuvonen et al to be due to the substituent-sensitive polarization of the N-C-O system. [24] The trans and cis series in the present work offered an interesting opportunity for the study of this type of reverse trend in the substituent effect (σ F ) on the calculated SCS values.…”

Comparison of the 13C (C = N) chemical shifts of substituted N‐(phenyl‐ethylene)‐anilines and substituted N‐(benzylidene)‐anilines

“…The substituted anilines XArCR = NArY have been attracted widespread attention because of its special nonlinear optical properties. [1][2][3][4][5][6][7][8][9][10] Their molecules have a π-electron conjugate system carrying a group at one end and another group at the opposite end, so their optical and electrical properties are more susceptible to subtle changes of the molecular structures. Therefore, it is a meaningful work to probe the substituent effect on its regularity of molecular internal charge distribution for understanding and predicting the physicochemical property of this kind of compounds.…”

“…Neuvonen [3][4][5][6][7][8][9][10][11][12] has investigated the substituent effects on the electronic characteristic of the C = N bridging group in substituted N-(benzylidene)-anilines XArCH = NArY (abbreviated XBAYs) with the 13 C NMR chemical shifts δ C (C = N) of C = N bond and obtained the valuable results: (1) for the X-substituents: electron-withdrawing group (EWG) cause shielding, while electron-donating group (EDG) behave oppositely; (2) in contrast, for the Y-substituents: EWG cause deshielding, while EDG cause shielding of the C = N bond. Neuvonen [9,10] pointed out: 'the presence of the specific cross-interaction between X and Y could be verified', but this specific cross-interaction effect was not be quantified at that time. Recently, Cao [18][19][20] et al developed Neuvonen's research by exploring the other properties of XBAYs and proposed the parameter Δσ 2 to measure the substituent-specific cross-interaction effect between substituents X and Y.…”