Ab initio calculations on 4-substituted benzoic acids; a further theoretical investigation into the nature of substituent effects in aromatic derivatives

1977 ◽  
Vol 55 (9) ◽  
pp. 1567-1574 ◽  
Author(s):  
Paul G. Mezey ◽  
William F. Reynolds
Keyword(s):  
Ab Initio ◽  
Field Effect ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Electron System ◽  
Acid Dissociation ◽  
Molecular Orbital Calculations ◽  
Atomic Charges ◽  
Benzoic Acids ◽  
Substituted Benzoic Acids

Ab initio (STO-3G) molecular orbital calculations for 4-substituted benzoic acids and XCH3–HCO2H pairs are used to derive a theoretical field, TF and resonance, TR(BA), substituent scale. Comparison with previous calculations for 4-substituted styrenes shows that a common field scale can be used for different systems but that different resonance scales are necessary, depending upon the electronic nature of the probe group. The field effect primarily reflects the direct electrostatic interaction between the substituent and the carboxylic acid. However, there are also significant contributions due to field-induced polarization of the intervening phenyl π electron system. By contrast, the π polarization effect seems to be the dominant field effect in the case of non-interacting probes (such as carbon atomic charges or chemical shifts). A very close parallel is noted between substituent effects upon atomic charges and acid dissociation energies.

An investigation into the origins of polar substituent effects upon 19F chemical shifts, using 4-substituted β,β-difluorostyrenes

1980 ◽  
Vol 58 (8) ◽  
pp. 839-845 ◽  
Author(s):  
William F. Reynolds ◽  
Victoria G. Gibb ◽  
Nick Plavac
Keyword(s):  
Chemical Shift ◽  
Electron Density ◽  
Molecular Orbital ◽  
Excellent Agreement ◽  
Field Effect ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Molecular Orbital Calculations ◽  
Chemical Shift Difference ◽  
Polar Substituent

19F, 13C, and 1H chemical shifts have been determined for β,β-difluorostyrene and eight 4-substituted derivatives. The β-fluorine chemical shift difference, ΔδF, is used to evaluate the constant in the Buckingham equation. A = 3.0 × 10−11 esu for C—F bonds which is in excellent agreement with the value derived by Adcock and Khor. This allows accurate estimates of direct field effect contributions to 19F chemical shifts in aryl fluorides. Substituent parameter correlations demonstrate that the primary polar effect on 19F chemical shifts is field-induced π polarization. Abinitio molecular orbital calculations confirm that the substituent-induced 19F chemical shifts reflect changes in fluorine π electron density.

scholarly journals Investigations of Substituent Effects by Nuclear Magnetic Resonance Spectroscopy and All-valence Electron Molecular Orbital Calculations. II. 4-Substituted α-Methylstyrenes and α-t-Butylstyrenes

1973 ◽  
Vol 51 (6) ◽  
pp. 915-926 ◽  
Author(s):  
Gordon K. Hamer ◽  
Ian R. Peat ◽  
W. F. Reynolds
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Electron System ◽  
Resonance Spectroscopy ◽  
Molecular Orbital Calculations ◽  
Electronic Effects ◽  
Partial Explanation ◽  
Charge Densities ◽  
Related Compounds ◽  
Molecular Framework

Substituent-induced 1H chemical shifts (S.C.S.) for 19 4-substituted α-methyl- and α-t-butylstyrenes have been determined at infinite dilution in C6H12 and 13C S.C.S. have been determined for 0.4 M solutions in CCl4. S.C.S. are correlated with field and resonance substituent parameters and compared with charge densities determined by CNDO/2 MO calculations. The variation of S.C.S. with the dihedral angle, ρ, between phenyl and vinyl groups and the overall pattern of S.C.S. can be largely accounted for by a model of substituent effects based on field, resonance, and π polarization effects, with conjugative interactions varying as cos2ρ. Both 13C chemical shifts and charge densities indicate that the π polarization effect consists of two components: (1) a through-space polarization of the vinyl system by the polar C—X bond and (2) polarization of the entire conjugated styrene π electron system. However, significant deviations are noted for some of the 1H S.C.S. correlations. The CNDO/2 calculations indicate that these deviations are primarily due to electronic effects not predicted by the model outlined above. CNDO/2 calculations for related compounds provide a partial explanation by indicating that the magnitude of the field effect depends upon the nature of the molecular framework.

Investigations of Substituent Effects by Nuclear Magnetic Resonance Spectroscopy and All-valence Electron Molecular Orbital Calculations. I, 4-Substituted Styrenes

1973 ◽  
Vol 51 (6) ◽  
pp. 897-914 ◽  
Author(s):  
Gordon K. Hamer ◽  
Ian R. Peat ◽  
William F. Reynolds
Keyword(s):  
Field Effect ◽  
Chemical Shifts ◽  
Hydrogen Charge ◽  
Substituent Effects ◽  
Conclusive Evidence ◽  
Resonance Spectroscopy ◽  
Molecular Orbital Calculations ◽  
Electronic Effects ◽  
Charge Densities ◽  
Self Consistent

1H and 13C chemical shifts have been determined for over 20 4-substituted styrenes under conditions corresponding to infinite dilution in a non-polar medium. Correlations of the internal chemical shift difference for the β vinyl protons, Δδ(B − C) with electric field components estimated by a classical electrostatic calculation, with the field parameter F, and with hydrogen charge densities estimated by CNDO/2 MO calculations provide conclusive evidence for the existence of a through-space field effect. CNDO/2 calculations for 4-substituted 1-vinylbicyclo[2.2.2]octanes and ethylene–methylX pairs indicate that this through-space field effect has a geometric dependence similar to that predicted by the Buckingham equation.Correlations of vinyl 1H and 13C chemical shifts and charge densities with field, F, and resonance, R, parameters provide a self-consistent picture of electronic effects in these compounds. 1H chemical shifts for some derivatives are affected by magnetic effects but this does not obscure the overall pattern of electronic effects. This pattern of electronic effects can be completely accounted for by a model which assumes that substituent effects can be transmitted through space (field effects), via conjugative interactions (resonance effects) or by polarization of the styrene π electron system by the polar C—X bond (π polarization effects). The latter effect appears to be more important than previously realized.1H correlations with F and R are used to estimate self-consistent and apparently reasonable Δχ values for C≡N and C≡C—H groups and F and R values for carbonyl substituents and (CH3)3M substituents (M = Si, Ge, Sn, and Pb). The halogens give anomalous results. A comparison of various correlations suggests that these anomalies are magnetic in origin.

Chemometrical Analysis of Substituent Effects. XIII. Comparison of Substituent Effects on Dissociation and Chemical Shift in 13C NMR Spectra of Mono- and Disubstituted Benzoic Acids

2000 ◽  
Vol 65 (1) ◽  
pp. 106-116 ◽  
Author(s):  
Jiří Kulhánek ◽  
Oldřich Pytela ◽  
Antonín Lyčka
Keyword(s):  
Chemical Shift ◽  
Latent Variable ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Principal Component ◽  
Data Matrix ◽  
Steric Effects ◽  
Benzoic Acids ◽  
Indicator Variable ◽  
Substituted Benzoic Acids

The 13C chemical shifts have been measured of the carboxyl carbon atoms for all the 2-, 3-, and 4-substituted benzoic acids with H, CH3, CH3O, F, Cl, Br, I, and NO2 substituents, as well as for all 3,4-, 3,5-, and 2,6-disubstituted benzoic acids with combinations of CH3, CH3O, Cl (or Br), NO2 substituents and for symmetrically 2,6-disubstituted derivatives with Et, EtO, PrO, i-PrO, and BuO substituents. The chemical shifts of carboxylic group carbon atoms of the 3- and 4-substituted derivatives show correlation only with the substituent constants σI. For the 2-substituted derivatives was found the dependence only on σI and on the υ constant describing steric effects (s = 0.122, R = 0.996, without the CH3 derivative which has a distinct anisotropic effect). The substituent effects on the carboxylic carbon chemical shift show additivity with 3,4-, 3,5-, and 2,6-substituents, and the 2,6-disubstituted derivatives show a linear synergic effect of substituents due obviously to the steric hindrance to resonance. Application of the principal component analysis to the data matrix involving all the combinations of mono- and disubstitution involving the above-mentioned substituents has proved an identical substituent effect from all the positions on the chemical shift described by one latent variable, steric effects and anisotropic behaviour of methyl at the 2 and 2,6 positions being predominantly described by the second latent variable (with the total explained variability of 99.5%). Comparison of substituent effects on the chemical shift of carboxylic carbon with that on the dissociation constant measured in the same solvent has confirmed the anisotropy due to ortho methyl group, the ortho halogen substituents in monosubstituted derivatives also having a different effect. The dependence of chemical shift on pKa was not very close for the derivatives studied (s = 1.005, R = 0.690). The inclusion of anisotropy of ortho alkyl group by means of an indicator variable improved the correlation (s = 0.533, R = 0.925), and omitting of 2-F, 2-Cl, 2-Br, and 2-I substituents gave a regression without deviating points (s = 0.352, R = 0.968).

SUBSTITUENT EFFECTS ON13C CHEMICAL SHIFTS OF CARBOXYL CARBONS IN SUBSTITUTED BENZOIC ACIDS

1974 ◽  
Vol 3 (7) ◽  
pp. 765-768 ◽  
Author(s):  
Jun Niwa ◽  
Mitsuru Yamazaki
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Benzoic Acids ◽  
Substituted Benzoic Acids

Chemometric Analysis of Substituent Effects. VII. Inductive Effect as a Basic Substituent Effect. Isoeffect Substituent Constant

1995 ◽  
Vol 60 (8) ◽  
pp. 1316-1332 ◽  
Author(s):  
Oldřich Pytela ◽  
Aleš Halama
Keyword(s):  
Inductive Effect ◽  
Chemical Shifts ◽  
Quantitative Description ◽  
Substituent Effects ◽  
Intersection Point ◽  
Chemometric Analysis ◽  
Reaction Centre ◽  
Substituent Constant ◽  
Modified Method ◽  
Substituted Benzoic Acids

The paper deals with chemometric analysis of the inductive effect. The notion of inductive effect is discussed, and unambiguous definitions are given for the notions of triad: reaction centre-basic skeleton-substituent, and the therewith connected definitions of inductive effect. For a quantitative description of inductive effect 7 types of chemical models were selected including noncyclic compounds, cyclic, and bicyclic compounds, derivatives of quinuclidine, 3-substituted benzoic acids, sulfonamides and pyridines. Altogether 139 sets of experimental data from literature have been used including altogether 1 294 points (9.3 points per set, 5 points at least) reflecting substituent effects of 34 substituents. It has been found that for a standard model the dissociation of substituted bicycloalkanecarboxylic acids only is satisfactory, all the other models reflecting also the mesomeric effects to variable extent (up to 10%). A distinctly different substitution behaviour was observed with 19F and 13C NMR chemical shifts of 4-substituted 1-fluoro- or 1-methylbicyclo[2.2.2]octanes. The earlier suggested model of substituent effects based on different way of transmission of substituent effects (3 classes) has been used for separating the inductive and mesomeric effects: it is mathematically presented as a set of straight lines with the intersection point at the so-called isoeffect substituent constant. Using the modified method of conjugated deviations a chemometric scale has been created for the inductive effect which agrees very well with the conventional scales given in literature; the only differences were observed for F and CH=O substituents (which are overestimated and underestimated, respectively, in literature). In the context given the inductive effect appears as a fundamental quantity forming a basis for quantitative description of other effects transferred by electrons.

Kinetic study of hydrolysis of benzoates. part xxvii. ortho substituent effect in alkaline hydrolysis of phenyl esters of substituted benzoic acids in aqueous Bu4NBr

2009 ◽  
Vol 74 (1) ◽  
pp. 29-42 ◽  
Author(s):  
Vilve Nummert ◽  
Mare Piirsalu ◽  
Signe Vahur ◽  
Oksana Travnikova ◽  
Ilmar A. Koppel
Keyword(s):  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Pure Water ◽  
Substituent Effects ◽  
Benzoic Acids ◽  
Resonance Effects ◽  
The Media ◽  
Substituted Benzoic Acids ◽  
Hydrolysis Of ◽  
Ortho Substituent

The second-order rate constants k (in dm3 mol–1 s–1) for alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C6H4CO2C6H5, have been measured spectrophotometrically in aqueous 0.5 and 2.25 M Bu4NBr at 25 °C. The substituent effects for para and meta derivatives were described using the Hammett relationship. For the ortho derivatives the Charton equation was used. For ortho-substituted esters two steric scales were involved: the EsB and the Charton steric (υ) constants. When going from pure water to aqueous 0.5 and 2.25 M Bu4NBr, the meta and para polar effects, the ortho inductive and resonance effects in alkaline hydrolysis of phenyl esters of substituted benzoic acids, became stronger nearly to the same extent as found for alkaline hydrolysis of C6H5CO2C6H4-X. The steric term of ortho-substituted esters was almost independent of the media considered. The rate constants of alkaline hydrolysis of ortho-, meta- and para-substituted phenyl benzoates (X-C6H4CO2C6H5, C6H5CO2C6H4-X) and alkyl benzoates, C6H5CO2R, in water, 0.5 and 2.25 M Bu4NBr were correlated with the corresponding IR stretching frequencies of carbonyl group, (ΔνCO)X.

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