The dependence of vanadate phenyl ester formation on the acidity of the parent phenols

1988 ◽  
Vol 66 (10) ◽  
pp. 2565-2569 ◽  
Author(s):  
Bruno Galeffi ◽  
Alan S. Tracey
Keyword(s):  
Formation Constants ◽  
Resonance Spectroscopy ◽  
Resonance Effects ◽  
Linear Free Energy ◽  
Ester Formation ◽  
Inductive Effects ◽  
Energy Relationships ◽  
Parameter Approach ◽  
D Orbitals ◽  
Aqueous Acetone Solution

The condensation of vanadate (VO4H21−) with a variety of substituted phenols in aqueous acetone solution has been studied by 51V nuclear magnetic resonance spectroscopy. The formation constants for the various product esters were determined, as were their respective pKa values. Inductive and resonance contributions to vanadate ester formation were investigated using the dual substituent parameter approach. This procedure did not succeed particularly well, although trends were clearly observed. Correlations with Hammett constants were compared with those of the dual parameter approach. The observation of some linear free-energy relationships was interpreted to mean that the inductive and resonance parameters generally ascribed to the various phenols are not directly applicable to vanadate ester formation where d orbitals are probably involved. The results did indicate that resonance effects have a significantly greater influence on ester formation than do inductive effects.

scholarly journals Effects of substituents on the 1H-NMR chemical shifts of 3-methylene-2-substituted-1, 4-pentadienes

2003 ◽  
Vol 68 (7) ◽  
pp. 525-534 ◽  
Author(s):  
Natasa Valentic ◽  
Gordana Uscumlic
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Electronic Effects ◽  
Resonance Effects ◽  
Charge Densities ◽  
Linear Free Energy ◽  
Energy Relationships ◽  
Consistent Picture ◽  
Vinyl Group ◽  
Proton Chemical Shifts

The principle of linear free energy relationships was applied to the 1H chemical shifts of the ?-vinyl proton atoms of 3-methylene-2-substituted-1,4-pentadienes. The correlations of the proton chemical shifts with Swain and Lupton substituent parameters provide a mutually consistent picture of the electronic effects in these compounds. The overall pattern of proton chemical shifts can be largely accounted for by a model of substituent effects based on field, resonance and ? polarization effects. Owing to the particular geometric arrangement of the vinyl group in 3-methylene-2-substituted-1,4-pentadienes, the ?-vinyl protons HB and HC have different sensitivities to polar and resonance effects. The different sensitivities of the 1H chemical shifts to resonance effects reveals some effects not predicted by the model outlined above. Evidence is presented that demonstrates that both the 1H and 13C chemical shifts for these compounds reflect their ground-state charge densities.

Vanadium(V) oxyanions. The dependence of vanadate alkyl ester formation on the pKa of the parent alcohols

1988 ◽  
Vol 66 (9) ◽  
pp. 2294-2298 ◽  
Author(s):  
Alan S. Tracey ◽  
Bruno Galeffi ◽  
Soroush Mahjour
Keyword(s):  
Aqueous Solution ◽  
Nuclear Magnetic Resonance ◽  
Free Energy ◽  
Resonance Spectroscopy ◽  
Linear Free Energy Relationship ◽  
Alkyl Esters ◽  
Linear Free Energy ◽  
Ester Formation ◽  
Interesting Correlation ◽  
Extra Electron

The interaction of vanadate (VO4H21−) with a variety of alkyl alcohol's (ROH) covering about seven pKa units of acidity have been studied in aqueous solution by 51V nuclear magnetic resonance spectroscopy. A linear free energy relationship between the equilibrium constant for the formation of the vanadate monoester (HOVO3R1−) and the acidity of the alcohol was established at 23 °C. The correlation was found to be [Formula: see text] where K = [HOVO3R1−]/[VO4H21−][ROH]. This correlation was shown not to extend to ligands with π-bonding capability such as phenols or phosphates, where the products are highly favoured relative to the alkyl esters. An interesting correlation between pKa values of the product esters and the pKa of the parent alcohols was also observed. It was found that below a [Formula: see text] of about 15 the pKa values of the esters were essentially constant. However, above this value of 15 the pKa of the ester was found to increase rapidly with an increase in pKa of the alcohol. This result may indicate that the electron accepting ability of the metal is exhausted with the higher pKa alcohols, and the extra electron density is transferred to the oxygens, thus causing an increase in pKa of the ester.

scholarly journals Effect of substituents on the 13C-NMR chemical shifts of 3-methylene-4-substituted-1, 4-pentadienes - Part I

2003 ◽  
Vol 68 (2) ◽  
pp. 67-76 ◽  
Author(s):  
Natasa Valentic ◽  
Zeljko Vitnik ◽  
Sergei Kozhushkov ◽  
Majere de ◽  
Gordana Uscumlic ◽  
...  
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Heat Of Formation ◽  
Electronic Effects ◽  
Resonance Effects ◽  
Linear Free Energy ◽  
Energy Relationships ◽  
Consistent Picture ◽  
The One ◽  
Semi Empirical

The principles of linear free energy relationships were applied to the 13C substituent chemical shifts (SCS) of the carbon atoms in the unsaturated chain of 3-methylene-4-substituted-1,4-pentadienes. Correlations of the SCS with the substituent parameters of Swain and Lupton provide a mutually consistent picture of the electronic effects in these compounds. The pattern of the electronic effects can be fully rationalized by a model based on the direct transmission of substituent effects through-space (direct through-space field effects), and via conjugative interactions (resonance effects), or by substituent-induced polarization of the ?-system in the unsaturated chain (?-polarization effect). Semi-empirical MNDO-PM3 calculations suggest the s-cis conformation of 3-methylene-4-substituted-1,4-pentadienes as the one with minimal heat of formation.

Additive-multiplicative description of extrathermodynamic relations: Application to solvent effect

1990 ◽  
Vol 55 (3) ◽  
pp. 634-643 ◽  
Author(s):  
Oldřich Pytela
Keyword(s):  
Solvent Effect ◽  
Additive Model ◽  
Multiplicative Model ◽  
Data Matrix ◽  
Statistical Parameters ◽  
Model Application ◽  
Mutual Correlation ◽  
Linear Free Energy ◽  
Cross Terms ◽  
Energy Relationships

The paper is focused on evaluation of significance of the additive-multiplicative model of extrathermodynamic relations (linear free energy relationships) as compared with the additive model. Application of the method of conjugated deviations to a data matrix describing manifestations of solvent effects in 367 processes in solutions (6 334 data) has shown that introduction of cross-terms into the additive model is statistically significant for a model with two and particularly three parameters. At the same time the calculation has provided a new set of statistical parameters for description of solvent effect with application of the additive-multiplicative model. Compared with an analogous set designated for the additive model, the new parameters show a lower mutual correlation, retaining the same nature of the properties described, i.e. polarity-acidity (PAC parameter), polarity-basicity (PBC), and polarity-polarizability (PPC).

Sign in / Sign up

Export Citation Format

Share Document