scholarly journals Carbonyl Addition Reactions: Factors Affecting the Hydrate–Hemiacetal and Hemiacetal–Acetal Equilibrium Constants

1975 ◽  
Vol 53 (6) ◽  
pp. 898-906 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Carbonyl Compounds ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Steric Effects ◽  
Addition Reactions ◽  
Free Energies ◽  
Electronic Effects ◽  
Factors Affecting ◽  
Analogous Formula

Equilibrium constants for hydrate–hemiacetal interconversion in aqueous solution at 25° have been measured for four fluorinated carbonyl compounds: compound, alcohol, K4 (M−1): CF3CHO, C2H5OH, 2.3; CF3COCH3, CH3OH, 1.0; CF3COPh, CH3OH, 3.5; CF3COCF3, CH3OH, 0.14. These values, combined with values from the literature, permit an examination of substituent effects upon the equilibrium constant for[Formula: see text]The free energy change for this process, corrected for symmetry and steric effects, follows the equation[Formula: see text]Thus electronic effects upon this equilibrium are generally small and in fact are often smaller than steric effects.This analysis permits and justifies the calculation of free energies of formation of [Formula: see text] compounds from the (more generally measurable) free energies of formation of the analogous [Formula: see text] compounds.

scholarly journals Thermodynamics of ester and orthoester formation from trifluoroacetic acid

1976 ◽  
Vol 54 (2) ◽  
pp. 202-209 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Equilibrium Constant ◽  
Trifluoroacetic Acid ◽  
Sodium Methoxide ◽  
Standard Free Energy ◽  
Steric Effects ◽  
Addition Reactions ◽  
Free Energies ◽  
Acetic Acids

The equilibrium constant for the addition of sodium methoxide to methyl trifluoroacetate, in methanol as solvent, has been measured by 19F nmr, and is 7 M−1. From this was calculated an equilibrium constant, 2 × 10−4 M−1, for addition of methanol to the ester. The equilibrium constant for formation of methyl trifluoroacetate in aqueous solutions is 0.06 M−1. These results, with literature data, permit calculation of the free energies of formation in aqueous solution of orthotrifluoroacetic acid and its mono-, di-, and trimethyl esters. These in turn permit calculation of the standard free energy changes for addition of water and methanol to trifluoroacetic acid and its methyl ester. These combined with the analogous values for formic and acetic acids permit evaluation of ρ* values for these addition reactions. Linear plots are obtained if correction is made for steric effects, and the ρ* values are somewhat larger, 2.1–2.9, than was observed for the analogous carbonyl addition reactions.

Acid Ionizations of Nitroalkanes in Aqueous Solution

1973 ◽  
Vol 51 (12) ◽  
pp. 1941-1944 ◽  
Author(s):  
Takeki Matsui ◽  
Loren G. Hepler
Keyword(s):  
Aqueous Solution ◽  
Carboxylic Acids ◽  
Equilibrium Constants ◽  
Free Energies ◽  
Methyl Substitution ◽  
Calorimetric Measurements ◽  
Acid Ionizations

Calorimetric measurements have led to ΔH0 values for ionization of nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane in aqueous solution at 298°K. Combinations of these enthalpies with free energies from equilibrium constants for ionization have led to ΔS0 values for the ionization reactions. It is noted that the trend toward decreasing pK with methyl substitution in nitroalkanes is unusual compared to phenols and carboxylic acids. Similarly, correlations of ΔS0 with ΔG0 and ΔH0 are different for nitroalkanes than for other acids.

Thermodynamic functions of ionization of t-butyl-substituted and methoxysubstituted phenols

1972 ◽  
Vol 25 (1) ◽  
pp. 75 ◽  
Author(s):  
PD Bolton ◽  
FM Hall ◽  
J Kudrynski
Keyword(s):  
Aqueous Solution ◽  
Thermodynamic Functions ◽  
Spectrophotometric Method ◽  
Substituent Effects ◽  
Steric Effects ◽  
Ionization Process ◽  
Ionization Constants ◽  
Temperature Range

Thermodynamic ionization constants of 2-t-butylphenol, 3-t-butylphenol, 4-t-butylphenol, 3,5-di-t-butylphenol, and 3,5-dimethoxyphenol have been measured in aqueous solution by an e.m.f./spectrophotometric method within the temperature range 5-60�C and the thermodynamic functions of ionization ΔG25, ΔH25, ΔS25, and ΔCp25 calculated. These results confirm the additivity of substituent effects noted previously for the ionization of 3,5-disubstituted phenols and indicate that this ionization process is relatively insensitive to steric effects.

Functional-group and substituent effects, both steric and electronic, upon the ultraviolet absorption spectra of some conjugated heteroenoid compounds

1967 ◽  
Vol 45 (13) ◽  
pp. 1567-1580 ◽  
Author(s):  
D. J. Currie ◽  
C. E. Lough ◽  
R. F. Silver ◽  
H. L. Holmes
Keyword(s):  
Functional Group ◽  
Inductive Effect ◽  
Substituent Effects ◽  
Wavelength Region ◽  
Steric Effects ◽  
Electronic Effects ◽  
Amino Groups ◽  
Empirical Parameter ◽  
Long Wavelength ◽  
Constant E

The positions of the long-wavelength maxima in the spectra of some 300 compounds of generalized formula I may be accommodated by assuming that the observed maximum is equal to that of styrene + Δλ (the conjugative effect of A) + Δλ′ (the inductive effect of B) + ΣΔλ″ (the sum of the steric effects of the A, B, and phenyl groups) + D (an empirical parameter related to X and Y). These arguments have been extended to the spectra of II. Δλ′ is related to the σ value for meta-substituted benzene derivatives or to σ*. D for meta- and [Formula: see text]para-substituted derivatives roughly correlates with the appropriate σ+ values, whereas D for ortho-substituted derivatives is related to a simple function involving the D value for para substitution and the steric substituent constant, ES. For compounds of generalized formula III, the electronic effects of the A and B groups cancel but the steric effects are additive.Multiple bands occur in the long-wavelength region of the spectra for compounds containing halogen, alkoxy, or amino groups. These groups are highly polarizable and are considered to function both as electron donors and electron sinks.

Electronic effects on enol acidity and keto-enol equilibrium constants for ring-substituted 2-tetralones

1999 ◽  
Vol 77 (5-6) ◽  
pp. 634-638 ◽  
Author(s):  
Xudong Yao ◽  
Ralph M Pollack
Keyword(s):  
Aqueous Solution ◽  
Charge Transfer ◽  
Systematic Study ◽  
Free Electron ◽  
Electron Pair ◽  
Equilibrium Constants ◽  
Hydroxyl Group ◽  
Negative Deviation ◽  
Electronic Effects ◽  
Free Electron Pair

Equilibrium constants for the ionization of a variety of phenyl-substituted 2-tetralones (pKaK), for the ionization of their enols (pKaE), and for keto-enol tautomerization (pKE) were determined. Hammett plots of pKaK and pKaE vs. σ- are linear with slopes (-ρ) of -1.66 ± 0.06 and -0.90 ± 0.03, respectively, except for deviations of the points corresponding to 6-nitro-2-tetralone (1b) and its enol. We have previously attributed the negative deviation of 1b from the correlation for the acidities of the ketones obtained with the more limited set of data to the lack of a free electron pair on C-1 of the free tetralone (Nevy et al.). The negative deviation of the point for 1b from the correlation for the acidities of the enols suggests that charge transfer from the hydroxyl group of the enol to the nitro group is less important than it is for phenols. This study represents the first systematic study of electronic effects on equilibria among ketone, enol, and enolate in aqueous solution. Key words: enol, acidity, equilibrium, substituent, conjugation.

Stereo-Electronic Effects in Substituted Phosphines: a Molecular Orbital Study

1985 ◽  
Vol 38 (1) ◽  
pp. 23 ◽  
Author(s):  
E Magnusson
Keyword(s):  
Molecular Orbital ◽  
Conformational Changes ◽  
Substituent Effect ◽  
Substituent Effects ◽  
Alkyl Substituent ◽  
Steric Effects ◽  
Electronic Effects ◽  
Electronic Response ◽  
Donor Acceptor ◽  
Geometrical Change

Substituent effects from directly bonded and remote groups in phosphines have been studied by ab initio molecular orbital methods in an attempt to discriminate between the electronic and steric effects of attached groups and determine how they are transmitted to phosphorus. Results of calculations are compared with experimentally determined basicities and acidities, ionization energies, inversion barriers and 31P N.M.R. results. The electronic consequences of steric effects are comparable in importance to direct electronic effects; in the PHn(CH3)3-n, series steric effects account for about half of the substituent effect on basicities and ionization potentials. The effects of steric bulk, modelled by bond angle constraint, are concentrated in the HOMO; by contrast, electronic effects on the HOMO are often minimal. Conformational changes include changes in geometry but the electronic response exceeds what would be expected for geometrical change alone and in NH2- and OH-substituted model compounds of the PH2X and PX3 series may be as great as that produced by changing the substituent. In remote substitution the effects are mainly due to charge displacement at phosphorus. Directly bound groups more often exert their effects by altering the balance between s and p orbitals in the bonding and in the non-bonding parts of the electron distribution but in ways which preclude correlation with electronegativity or other single-parameter measures of substituent properties. Donor/acceptor interactions are weaker in phosphorus(III) compounds than in the first-row analogues but the response to substitution in the density profile is much stronger around the more polarizable second-row element which explains why the alkyl substituent effect is greater for the donor properties of phosphines than amines while the effects of fluoro-substitution are weaker.

Tautomerization equilibria for phosphorous acid and its ethyl esters, free energies of formation of phosphorous and phosphonic acids and their ethyl esters, and pKa values for ionization of the P—H bond in phosphonic acid and phosphonic esters

1979 ◽  
Vol 57 (2) ◽  
pp. 236-239 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Equilibrium Constants ◽  
Phosphorous Acid ◽  
Triethyl Phosphite ◽  
Ethyl Esters ◽  
Free Energies ◽  
Phosphonic Acids ◽  
Hydroxy Compounds ◽  
Energy Relations

From data in the literature the free energies of formation in aqueous solution of triethyl phosphite and diethyl phosphonate can be calculated as −138.4 ± 1.7 and −165.1 ± 2.0 kcal mol−1, respectively. From these values, by application of free energy relations which we have published, the free energies of formation of the corresponding hydroxy compounds can be calculated and thence the equilibrium constants for tautomerization, which are 107.2, 108.7, and 1010.3 in favor of the tetracoordinate phosphonate tautomer for P(OEt)2OH, P(OEt)(OH)2, and P(OH)3, respectively. Using estimated pKa values for the tricoordinate phosphite species the tautomerization equilibria for the anions could also be calculated, as could the pKa values from the P—H bonds: 13, 26, and 38 for H—PO(OEt)2, H—PO2(OEt)−, and H—PO32−, respectively.

scholarly journals Substituent Effects Impact Surface Charge and Aggregation of Thiophenol-Labeled Gold Nanoparticles for SERS Biosensors

Biosensors ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 25
Author(s):  
Nolan File ◽  
Joseph Carmicheal ◽  
Alexey V. Krasnoslobodtsev ◽  
Nicole C. Japp ◽  
Joshua J. Souchek ◽  
...  
Keyword(s):  
Gold Nanoparticles ◽  
Surface Charge ◽  
Simultaneous Detection ◽  
Substituent Effects ◽  
High Sensitivity ◽  
Clinical Diagnostics ◽  
Binding Modes ◽  
Electronic Effects ◽  
Factors Affecting ◽  
Impact Surface

SERS immunoassay biosensors hold immense potential for clinical diagnostics due to their high sensitivity and growing interest in multi-marker panels. However, their development has been hindered by difficulties in designing compatible extrinsic Raman labels. Prior studies have largely focused on spectroscopic characteristics in selecting Raman reporter molecules (RRMs) for multiplexing since the presence of well-differentiated spectra is essential for simultaneous detection. However, these candidates often induce aggregation of the gold nanoparticles used as SERS nanotags despite their similarity to other effective RRMs. Thus, an improved understanding of factors affecting the aggregation of RRM-coated gold nanoparticles is needed. Substituent electronic effects on particle stability were investigated using various para-substituted thiophenols. The inductive and resonant effects of functional group modifications were strongly correlated with nanoparticle surface charge and hence their stability. Treatment with thiophenols diminished the negative surface charge of citrate-stabilized gold nanoparticles, but electron-withdrawing substituents limited the magnitude of this diminishment. It is proposed that this phenomenon arises by affecting the interplay of competing sulfur binding modes. This has wide-reaching implications for the design of biosensors using thiol-modified gold surfaces. A proof-of-concept multiplexed SERS biosensor was designed according to these findings using the two thiophenol compounds with the most electron-withdrawing substitutions: NO2 and CN.

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