ChemInform Abstract: Substituent Effects in 1H and 13C NMR Correlations of Chemical Shifts in para‐Substituted 5‐Arylmethylenehydantoins
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1H, 13C and 15N NMR spectra of the ring-substituted N-phenylglycines (1) and their ethyl esters (2) were measured in DMSO-d6. The chemical shift determinations and assignments are based on modern inverse 2D techniques (HMQC, HMBC). Dependences between chemical shifts and substituent constants show that the substituent effect is well transmitted to some side-chain atoms. There is a good correlation between δN1H and linear combinations of the inductive, σI, and resonance substituent constants, σR(-), for compounds 2. Similar results were obtained when the carbonyl carbon chemical shifts in both Series 1 and 2 were related to the substituent constants. Excellent linear dependences were obtained for nitrogen chemical shifts. The correlation coefficient for the linear dependence δ15N vs. linear combination of inductive and resonance substituent constants is high and it becomes even higher when a correction for the solvent effect is included. In general, the contribution of resonance to chemical shifts is much higher than that of polar effects. The results obtained show NHCH2CO2R to be a strong electron donor. © 1998 John Wiley & Sons, Ltd.
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Abstract The 13 C NMR spectra of 40 vicinally substituted 2‐ and 3‐nitropyridines were recorded. The observed chemical shifts are, in general, non‐additive. These results are discussed in terms of the effects of 2‐, 3‐ and 4‐substitutents on the ring carbons and of the position of the fixed nitro group and the substituent. The chemical shifts of the para carbon, with respect to the substitutent, follow well the dual substituent parameter approach, which shows their electronic origin. However, the substituent chemical shifts of both ipso and ortho positions can be rationalized, in terms of multiple parameter substituent correlation analysis, only on a approximate level.
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Abstract The effect of substituents on the proton chemical shifts and spin–spin coupling constants in ortho ‐, meta ‐ and para ‐substituted 5‐phenyltetrazoles (tetrazolic acids) in DMSO–CH 3 CN (1:1, v/v) was studied. With the meta ‐ and para ‐ substituted compounds the additivity rule of chemical shifts was obeyed, thereby enabling increments characterizing the effects of individual substituents in monosubstituted benzenes to be determined. By employing the Smith and Proulx equation, the chemical shifts of the aromatic protons were correlated with the F , R and Q substituent constants. The values of these constants are 1.02, −0.004 and 5.49, respectively, for the tetrazolyl substituent.
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Abstract The natural abundance 13 C n.m.r. spectra of a series of para ‐substituted ethylbenzenes, 4‐substituted‐1‐ethylnaphthalenes and a limited series of 6‐substituted‐2‐ethylnaphthalenes have been examined at low dilution in deuterochloroform solvent. The ethyl carbons and C ipso in the phenyl series (i.e. have been assigned, and substituent chemical shifts for these carbons calculated and analysed by the Dual Substituent Parameter treatment. (Chemical shifts of all ring carbons have been obtained, but not assigned). Generally speaking, electron‐withdrawing substituents lead to positive (i.e. downfield) substituent chemical shifts for CH 2 and negative substituent chemical shifts for C H 3 , i.e. ‘normal’ and ‘inverse’ behaviour respectively. C ipso in the phenyl series exhibits a ‘normal’ dependence. The dependences of the various substituent chemical shifts on inductive and resonance parameters are discussed, and compared with the behaviour of side chain carbons in other substituted benzene systems.
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Photochemical reactions of substituted 1-acetonaphthones in the presence of 2-morpholinoacrylonitrile were investigated. The type of reaction, photocycloaddition s. photosubstitution, is dependent on the nature of the additional substituent. The location of the additional substituent on the ring also affects the type of addition, [2 + 2] s. [4 + 2].
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Abstract Proton and carbon‐13 chemical shifts of para‐substituted stilbenes have been measured. 1 H‐ 1 H, 1 H‐ 13 C COSY spectra were obtained to analyze unambiguously the chemical shifts of protons and carbons. A long range coupling between 2‐H and α‐H was observed in a 1 H‐ 1 H COSY spectrum. The observed chemical shifts have been correlated with Hammett substituent parameters. Among ethenyl protons and carbons, all but the chemical shifts of α‐H show good correlation with both dual substituent parameters and single substituent parameters. In addition to this finding, the excellent linear correlations of C‐l, and 4′‐H of 4‐substituted trans‐stilbenes are also reported. Besides the correlations of chemical shifts with Hammett parameters, a good correlation between the chemical shifts and the calculated charges of position C‐4′ are reported.
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Based on the 13C NMR chemical shifts of more than 300 oxindole derivatives, substituent-induced chemical shifts have been calculated for this family of compounds. These substituent effects have been compared to those of monosubstituted benzenes and the correlation with the Hammett σ values and dual substituent parameters has also been tested. By means of these validated substituent effects, the 13C NMR chemical shifts of the oxindole skeleton containing various substituents can be accurately predicted.
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Abstract Evaluation by empirically derived equations for the Substituent effect (α, β, γ, δ) on the 13C NMR chemical shifts for C-3, C-4. C-5 and halomethyl-substituent carbon (C-6) in isoxazoles 1-5 [where C-3 substituent (R1) = H, alkyl or phenyl, C-4 Substituent (R2) = H, alkyl, and C-5 substituent (R3) = di-or trihalomethyl, methyl and H], taking as reference the compound la, is reported. From the calculated values for the α, β, γ, δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1–5. The 13 C chemical shifts of the C-3, C-4, C-5, C-6 of these compounds, can be estimated with good precision: 94% of the calculated chemical shifts are found to be within ±1.0ppm, and 100% are found to be within ±1.5ppm.
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Abstract 31P chemical shifts are reported for twenty aminoalkylphosphonic acids (APAs), nine 1-hydroxyalkyl phosphonic (HPAs) and six phosphonic acids (PAs). The protonation shifts and the substituent-induced effects (SCSs) of the amino and hydroxyl groups on the 31P NMR and α-carbon 13C NMR chemical shifts were calculated and discussed. Substituent shielding effects on phosphorus nucleus and deshielding effects on α-carbon are observed for both groups. Amino shielding effect on phosphorus nucleus is the sum of two interactions: 1) electron-withdrawing substituent effect propagated along the carbon chain, 2) hydrogen bonding and coulombic attaction between groups in the zwitterion forms. Both imply the increasing contribution of a P[dbnd]O resonance structure leading to the upfield S(P). Good linear correlation exist between chemical shifts of 1-hydroxyalkylphosphonic acids and the respective values of analogously constituted 1-aminoalkylphosphonic acids.
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