- Dissociation of naphthoic acids in non-aqueous media. Comparison of benzene and naphthalene skeletons
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Seven monosubstituted 1-naphthoic acids were synthesized by new or modified procedures, and their dissociation constants were measured potentiometrically at 25 °C in methanol, acetonitrile, dimethylformamide, and pyridine. Dissociation constants of these along with thirteen substituted 1-naphthoic acids and twenty-five substituted 2-naphthoic acids previously studied were measured at 25 °C in ethanol and dimethyl sulfoxide. The pKHA values of 3-and 4-substituted 1-naphthoic acids were treated by simple linear regression and principal component analysis, and the results were used for comparison of model compounds and of corresponding 3-and 4-substituted benzoic acids with the aim of comparison of benzene and naphthalene skeletons. It has been found, the 3 and 4 positions of the 1-naphthyl system can roughly be compared with the meta and para positions of benzene, respectively.
- Parik, Patrik,Wolfova, Jitka,Ludwig, Miroslav
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p. 385 - 394
(2007/10/03)
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- 13C NMR investigation of electronic interactions in 5-substituted 1-naphthonitriles
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Carbon-13 NMR chemical shifts of 5-Z-substituted 1-naphthonitriles (1; Z = H, F, Cl, Br, NH2, NMe2, CN, NO2, OMe, CHO, CO2Me) in deuteriochloroform and in neat trifluoroacetic acid (TFA) are reported. The CN carbon shifts are found to correlate well with the dual substituent parameters (DSPs). Negative values of the transmission coefficients in the DSP correlation give evidence of a reverse substituent electronic effect, which is associated with variations in π polarization of the CN multiple bond, due primarily to differences in the through-space field effects of the various Z. The effect diminishes for 1 in neat TFA because of the greater contribution of dipolar ArC+=N- to the resonance hybrid. Deviations of the aromatic carbon shifts from substituent chemical shift additivities are small, yet show distinct patterns for many of the carbon resonances. The deviations of the C-1 - CN ipso carbon shifts of 1 in neutral solvents and in TFA correlate roughly with the DSPs. They are attributable to changes in charge density at C-1 that arise as a consequence of substituent-induced changes in the polarity of the CN bond. The greater than expected shielding that is observed for the C-6 and C-8 resonances accords with reduced electron withdrawal by +R substituents and increased mesomeric activity by electron-donating groups, Z, in response to the CN-induced charge depletion within the adjacent aromatic ring. From the location of data for 5-methoxy-1-naphthonitrile (1; Z = OMe) in the chemical shift correlations of 1 in neat TFA, one can conclude that the methoxy group of this compound, unlike that of 1-methoxynaphthalene itself, is not significantly hydrogen-bonded by TFA.
- Schuster, Ingeborg I.
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p. 301 - 310
(2007/10/03)
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