Linear free energy relationship rate constants and basicities of N-substituted phenyl glycines in positronium-glycine complex formation

1987 ◽  
Vol 137 (5) ◽  
pp. 471-474 ◽  
Author(s):  
Rongti Chen (Y.T. Chen) ◽  
Jiachang Liang ◽  
Youming Du ◽  
Chun Cao ◽  
Dinzhen Yin ◽  
...  
Keyword(s):  
Free Energy ◽  
Complex Formation ◽  
Rate Constants ◽  
Linear Free Energy Relationship ◽  
Linear Free Energy

Benzhydrylium and tritylium ions: complementary probes for examining ambident nucleophiles

2015 ◽  
Vol 87 (4) ◽  
pp. 341-351 ◽  
Author(s):  
Armin R. Ofial
Keyword(s):  
Free Energy ◽  
Rate Constants ◽  
The Other ◽  
Steric Effects ◽  
Linear Free Energy Relationship ◽  
Reliable Tool ◽  
Linear Free Energy ◽  
Sensitivity Parameter ◽  
Meldrum's Acids ◽  
Kinetics Of

AbstractThe linear free energy relationship log k = sN(N + E) (eq. 1), in which E is an electrophilicity, N is a nucleophilicity, and sN is a nucleophile-dependent sensitivity parameter, is a reliable tool for predicting rate constants of bimolecular electrophile-nucleophile combinations. Nucleophilicity scales that are based on eq. (1) rely on a set of structurally similar benzhydrylium ions (Ar2CH+) as reference electrophiles. As steric effects are not explicitely considered, eq. (1) cannot unrestrictedly be employed for reactions of bulky substrates. Since, on the other hand, the reactions of tritylium ions (Ar3C+) with hydride donors, alcohols, and amines were found to follow eq. (1), tritylium ions turned out to be complementary tools for probing organic reactivity. Kinetics of the reactions of Ar3C+ with π-nucleophiles (olefins), n-nucleophiles (amines, alcohols, water), hydride donors and ambident nucleophiles, such as the anions of 5-substituted Meldrum’s acids, are discussed to analyze the applicability of tritylium ions as reference electrophiles.

Comparison of the nucleophilicities of alcohols and alkoxides

2005 ◽  
Vol 83 (9) ◽  
pp. 1554-1560 ◽  
Author(s):  
Thanh Binh Phan ◽  
Herbert Mayr
Keyword(s):  
Free Energy ◽  
Key Words ◽  
Rate Constants ◽  
Correlation Equation ◽  
Linear Free Energy Relationship ◽  
Hydroxide Solution ◽  
Linear Free Energy ◽  
S Parameters ◽  
Nucleophilic Reactivity ◽  
Kinetics Of

The kinetics of the reactions of benzhydrylium ions with some alcohols and alkoxides dissolved in the corresponding alcohols were photometrically investigated. Using the correlation equation log k (20 °C) = s(E + N), the N and s parameters of methoxide, ethoxide, n-propoxide, and isopropoxide in alcohol–acetonitrile (91:9, v/v) were determined. The cosolvent acetonitrile has only a little influence on the rate constants of the reactions of alcohols and alkoxides. The order of N values (OH– << MeO– < EtO– < n-PrO– < i-PrO–) shows that alkoxides differ only moderately in reactivity but are considerably more nucleophilic than hydroxide. As a consequence, the nucleophilic reactivity of a 0.5 mmol/L aqueous hydroxide solution increases by a factor of 13 when 10% (v/v) methanol is added. In 1–10 mmol/L alkoxide solutions in alcohols, weak electrophiles react considerably faster with alkoxides than with the corresponding alcohols. With increasing electrophilicity, the preference for alkoxides decreases, and electrophiles of –3 < E < 3 react with alkoxides (1–10 mmol/L) and alcohols with comparable rates. Stronger electrophiles will react with alcohols exclusively when alkoxides are present in concentrations ≤10 mmol/L. Key words: kinetics, alcohol, alkoxide, linear free energy relationship, nucleophilicity.<

Substituent Effects on the Chymotrypsin-Catalyzed Hydrolysis of Specific Ester Substrates

1971 ◽  
Vol 49 (2) ◽  
pp. 210-217 ◽  
Author(s):  
R. E. Williams ◽  
M. L. Bender
Keyword(s):  
Free Energy ◽  
Rate Constants ◽  
Substituent Effects ◽  
Phenyl Group ◽  
Linear Free Energy Relationship ◽  
Acylation Reaction ◽  
General Base ◽  
Linear Free Energy ◽  
Base Mechanism ◽  
Hydrolysis Of

The substituent effect on the chymotrypsin-catalyzed hydrolysis of several phenyl esters of specific substrates has been studied. The second-order acylation rate constants (kcat/Km(app)) obey a linear free energy relationship with ρ = +0.63 for phenyl hippurates and ρ = +0.46 for phenyl N-benzyloxycarbonyl-L-tryptophanates when substituents are introduced into the phenyl group of the ester function. These results further support the previously proposed general acid – general base mechanism for the acylation reaction and the formation of a tetrahedral intermediate in the course of the reaction.

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.

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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