Comparison of acidity function and linear free energy basicity constants of amides, phenylureas, and nitroanilines

1973 ◽  
Vol 26 (10) ◽  
pp. 2083 ◽  
Author(s):  
JW Barnett ◽  
CJ O'Conner
Keyword(s):  
Free Energy ◽  
Basicity Constant ◽  
Acidity Function ◽  
Linear Free Energy ◽  
The Difference

The Bunnett-Olsen linear free relationship1 has been used to determine the thermodynamic basicity constants, KBH+, of 22 amides, 8 phenylureas, and 9 nitroanilines. These values have been compared with the basicity constant determined by plotting log I against the appropriate acidity function. For amides and phenylureas the two values of pKBH+ differ by <0.3 logarithm units, whereas for nitroanilines the difference increases with decreasing basicity and may be as large as 2.1 logarithm units.

Synthesis and characterization of a series of 1-methyl-4-[2-aryl-1-diazenyl]piperazines and a series of ethyl 4-[2-aryl-1-diazenyl]-1-piperazinecarboxylates

2004 ◽  
Vol 82 (8) ◽  
pp. 1294-1303 ◽  
Author(s):  
Vanessa Renée Little ◽  
Keith Vaughan
Keyword(s):  
Free Energy ◽  
Chemical Shifts ◽  
Linear Free Energy Relationship ◽  
Piperazine Ring ◽  
Linear Free Energy ◽  
In Series ◽  
Methylene Groups ◽  
Diazonium Coupling ◽  
The Difference

1-Methylpiperazine was coupled with a series of diazonium salts to afford the 1-methyl-4-[2-aryl-1-diazenyl]piperazines (2), a new series of triazenes, which have been characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, and elemental analysis. Assignment of the chemical shifts to specific protons and carbons in the piperazine ring was facilitated by comparison with the chemical shifts in the model compounds piperazine and 1-methylpiperazine and by a HETCOR experiment with the p-tolyl derivative (2i). A DEPT experiment with 1-methylpiperazine (6) was necessary to distinguish the methyl and methylene groups in 6, and a HETCOR spectrum of 6 enabled the correlation of proton and carbon chemical shifts. Line broadening of the signals from the ring methylene protons is attributed to restricted rotation around the N2-N3 bond of the triazene moiety in 2. The second series of triazenes, the ethyl 4-[2-phenyl-1-diazenyl]-1-piperazinecarboxylates (3), have been prepared by similar diazonium coupling to ethyl 1-piperazinecarboxylate and were similarly characterized. The chemical shifts of the piperazine ring protons are much closer together in series 3 than in series 2, resulting in distortion of the multiplets for these methylenes. It was noticed that the difference between these chemical shifts in 3 exhibited a linear free energy relationship with the Hammett substituent constants for the substituents in the aryl ring. Key words: triazene, piperazine, diazonium coupling, NMR, HETCOR, linear free energy relationship.

LINEAR FREE ENERGY RELATIONSHIPS CONCERNING EQUILIBRIA IN MODERATELY CONCENTRATED MINERAL ACIDS: A SIMPLE METHOD FOR ESTIMATING pK's OF WEAK BASES

1966 ◽  
Vol 44 (16) ◽  
pp. 1899-1916 ◽  
Author(s):  
J. F. Bunnett ◽  
Fredric P. Olsen
Keyword(s):  
Free Energy ◽  
Acid Concentration ◽  
Standard Form ◽  
Acidity Function ◽  
Linear Free Energy Relationships ◽  
Simple Method ◽  
Linear Free Energy ◽  
Equilibrium Quotient ◽  
Mineral Acids ◽  
Energy Relationships

Linear relationships exist between the logarithms of equilibrium quotients, [SH+]/[S][H+], of diverse bases as they vary with acid concentration in moderately concentrated mineral acids. For purposes of formulating these linear free energy relationships in standard form, the equilibrium quotient for protonation of a hypothetical aromatic primary amine of pKa zero has been chosen as horizontal coordinate; this is given by (−H0 − log [H+]). Log ([SH+]/[S]) + H0 is plotted against (H0 + log [H+]). The slope, [Formula: see text] of the linear plot is a parameter which characterizes the response of the equilibrium quotient to changing acid concentration. The intercept represents the thermodynamic pKa of the base. This constitutes a general method for estimating the pKa of any base which undergoes protonation in moderately concentrated mineral acid, with reference to the single acidity function, H0. For bases of diverse type, pK's estimated by this method are in good agreement with those estimated by the acidity function method. Use of the new correlation procedure as a check on the validity of several acidity functions and its application to equilibria not involving proton gain or loss are also discussed.

Applicability of the HT acidity function to the protonation of thioamides, thioureas, and thionesters

1977 ◽  
Vol 55 (12) ◽  
pp. 2331-2335 ◽  
Author(s):  
John T. Edward ◽  
Gary D. Derdall ◽  
Sin Cheong Wong
Keyword(s):  
Free Energy ◽  
Sulfuric Acid ◽  
Protonation Constants ◽  
Acidity Function ◽  
Linear Free Energy Relationships ◽  
Acceptable Accuracy ◽  
Aqueous Sulfuric Acid ◽  
Linear Free Energy ◽  
Energy Relationships

The protonation of eleven thioamides, five thioureas, and four thionbenzoates in aqueous sulfuric acid has been found to follow the HT acidity function with acceptable accuracy. Protonation constants pKTH+ obtained by use of HT agreed fairly well with pKTH+ values obtained by the Bunnett–Olsen method, but less well with those obtained by the Marziano–Cimino–Passerini procedure. Linear free-energy relationships of pKTH+ values are discussed.

Dissociation constants of monosubstituted diphenylamines and an optimized construction of acidity function

1983 ◽  
Vol 48 (8) ◽  
pp. 2368-2375 ◽  
Author(s):  
Oldřich Pytela ◽  
Pavel Vetešník
Keyword(s):  
Free Energy ◽  
Sulphuric Acid ◽  
Concentration Ratio ◽  
Dissociation Constants ◽  
Acidity Function ◽  
Linear Free Energy Relationships ◽  
Linear Free Energy ◽  
Energy Relationships ◽  
Sulphuric Acid Concentration

Eleven monosubstituted diphenylamines have been synthetized, and concentration ratio of the protonated and free bases has been measured in aqueous sulphuric acid in the concentration range 1.0 . 10-3 to 9.0 mol l-1. An algorithm has been suggested and used for determination of optimized values of pK and H'' acidity function within sulphuric acid concentration range 0.05 to 9.0 mol l-1. The results have been compared with literature data and discussed in terms of theory of acidity functions and linear free energy relationships.

scholarly journals Estimating Free Energies of Formation of Titanate () and Zirconate () Pyrochlore Phases of Trivalent Lanthanides and Actinides

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
Anpalaki J. Ragavan ◽  
Dean V. Adams
Keyword(s):  
Free Energy ◽  
First Principles ◽  
Linear Free Energy Relationship ◽  
Free Energies ◽  
Empirical Parameter ◽  
Trivalent Lanthanides ◽  
Linear Free Energy ◽  
Free Energy Of Formation ◽  
The Difference ◽  
Energy Of Formation

A linear free energy relationship was developed to predict the Gibbs free energies of formation (, in kJ/mol) of crystalline titanate (M2Ti2O7) and zirconate (M2Zr2O2) pyrochlore families of trivalent lanthanides and actinides (M3+) from the Shannon-Prewitt radius of M3+ in a given coordination state (, in nm) and the nonsolvation contribution to the Gibbs free energy of formation of the aqueous M3+ (). The linear free energy relationship for M2Ti2O7 is expressed as . The linear free energy relationship for M2Zr2O7 is expressed as . Estimated free energies were within 0.73 percent of those calculated from the first principles for M2Ti2O7 and within 0.50 percent for M2Zr2O7. Entropies of formation were estimated from constituent oxides (J/mol), based on an empirical parameter defined as the difference between the measured entropies of formation of the oxides and the measured entropies of formation of the aqueous cation.

Hydrogen Atom Transfer Reaction Free Energy as a Predictor of Abiotic Nitroaromatic Reduction Rate Constants: A Comprehensive Analysis

2019 ◽  
Author(s):  
Dominic Di Toro ◽  
Kevin P. Hickey ◽  
Herbert E. Allen ◽  
Richard F. Carbonaro ◽  
Pei C. Chiu
Keyword(s):  
Free Energy ◽  
Hydrogen Atom ◽  
Hydrogen Atom Transfer ◽  
Energy Model ◽  
Second Order ◽  
Transfer Model ◽  
Atom Transfer ◽  
Order Rate ◽  
Linear Free Energy ◽  
Free Energy Model

<div>A linear free energy model is presented that predicts the second order rate constant for the abiotic reduction of nitroaromatic compounds (NACs). For this situation previously presented models use the one electron reduction potential of the NAC reaction. If such value is not available, it has been has been proposed that it could be computed directly or estimated from the electron affinity (EA). The model proposed herein uses the Gibbs free energy of the hydrogen atom transfer (HAT) as the parameter in the linear free energy model. Both models employ quantum chemical computations for the required thermodynamic parameters. The available and proposed models are compared using second order rate constants obtained from five investigations reported in the literature in which a variety of NACs were exposed to a variety of reductants. A comprehensive analysis utilizing all the NACs and reductants demonstrate that the computed hydrogen atom transfer model and the experimental one electron reduction potential model have similar root mean square errors and residual error probability distributions. In contrast, the model using the computed electron affinity has a more variable residual error distribution with a significant number of outliers. The results suggest that a linear free energy model utilizing computed hydrogen transfer reaction free energy produces a more reliable prediction of the NAC abiotic reduction second order rate constant than previously available methods. The advantages of the proposed hydrogen atom transfer model and its mechanistic implications are discussed as well.</div>

Absorption Spectra of Substituted 2-Phenylindan-1,3-Dion-2-YL Radicals in Solution

1983 ◽  
Vol 38 (12) ◽  
pp. 1337-1341
Author(s):  
J. Zechner ◽  
N. Getoff ◽  
I. Timtcheva ◽  
F. Fratev ◽  
St. Minchef
Keyword(s):  
Free Energy ◽  
Absorption Spectra ◽  
Flash Photolysis ◽  
Bathochromic Shift ◽  
Substitution Effects ◽  
Linear Free Energy Relationship ◽  
Linear Free Energy

Abstract Flash photolysis of a series of 2-phenylindandione-1,3 derivatives substituted in the 4′ position results in both the formation of stable benzylidenephthalides and of phenylindan-1,3-dion-2-yl radicals. The u. v. absorption maxima of these radicals are dependent on the solvent and show a bathochromic shift upon substitution. These substitution effects were correlated by means of a linear free energy relationship. Attempts were made to draw conclusions concerning the changes in the gap of the states involved and their curvature due to substitution.

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