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.

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.<

Hydrolysis of haloacetonitriles: LINEAR FREE ENERGY RELATIONSHIP, kinetics and products

1999 ◽  
Vol 33 (8) ◽  
pp. 1938-1948 ◽  
Author(s):  
Victor Glezer ◽  
Batsheva Harris ◽  
Nelly Tal ◽  
Berta Iosefzon ◽  
Ovadia Lev
Keyword(s):  
Free Energy ◽  
Linear Free Energy Relationship ◽  
Linear Free Energy ◽  
Hydrolysis Of

Substituent effects in naphthalene. III. Saponification of 6- and 7-substituted Methyl 2-naphthoates and application of the Hammett equation

1966 ◽  
Vol 19 (2) ◽  
pp. 221 ◽  
Author(s):  
PR Wells ◽  
W Adcock
Keyword(s):  
Free Energy ◽  
Alkaline Hydrolysis ◽  
General Feature ◽  
Substituent Effects ◽  
Linear Free Energy Relationship ◽  
Reaction Centre ◽  
Hammett Equation ◽  
P Values ◽  
Linear Free Energy ◽  
Aromatic Systems

The rates of alkaline hydrolysis in 70% v/v aqueous dioxan at 25� have been determined for the 6-and 7-NO2, 6- and 7-CN, 6- and 7-F, 6- and 7-Cl, 6- and 7-NMe2, 6-Me and 6-OMe substituted methyl 2-naphthoates, methyl 2- naphthoate, m-NO2, p-NO2, p-Me substituted methyl benzoates, and methyl benzoate. An examination of the application of the Hammett equation reveals that this linear free energy relationship applies with high precision but that it yields different p values for different substituent-reaction centre dispositions. This may be a general feature for all aromatic systems although in many cases the differences are not larger than the experimental uncertainties.

scholarly journals Reactivity-Selectivity Principle: Phenyl Group in Indazole Makes It More Lucid

2021 ◽  
Author(s):  
Sanjeev Rachuru ◽  
Jagannadham Vandanapu
Keyword(s):  
Free Energy ◽  
Undergraduate Students ◽  
Phenyl Group ◽  
Linear Free Energy Relationship ◽  
Resonance Structures ◽  
Linear Free Energy ◽  
Reaction Constants ◽  
Selectivity Principle

Linear free energy relationship (LFER) plots are constructed for the deprotonation equilibriums (pKaH+) of pyrazolium and indazolium (benzopyrazolium) cations. The reaction constants Taft * and Hammett  are found to be 2.75 and 1.32 for deprotonation (pKaH+) of pyrazolium and indazolium cations respectively. Higher value of Taft * than the Hammett  is explained in terms of extra stability of the indazolium cation due to its greater number of resonance structures. This article is an exercise to undergraduate students for writing different resonance structures of indazolium cation.

Hydrolysis of amides. VI. Dilute acid hydrolysis of N-alkyl substituted acetamides

1972 ◽  
Vol 25 (2) ◽  
pp. 303 ◽  
Author(s):  
PD Bolton ◽  
J Ellis ◽  
RD Frier ◽  
PC Nancarrow
Keyword(s):  
Free Energy ◽  
Acid Hydrolysis ◽  
Rate Constants ◽  
Rate Data ◽  
Linear Free Energy Relationships ◽  
Dilute Acid ◽  
Dilute Acid Hydrolysis ◽  
Linear Free Energy ◽  
Energy Relationships ◽  
Hydrolysis Of

Enthalpies and entropies of activation have been derived from rate constants measured over a range of temperature for the dilute acid hydrolysis of N-methyl- acetamide, N-ethylacetamide, N-n-propylacetamide, N-isopropylacetamide, N-n-butylacetamide, N-s-butylacetamide, N-isobutylacetamide, N-isopentyl-acetamide, N-n-hexylacetamide, N-cyclohexylacetamide, and N-benzylacetamide. An analysis of the rate data in terms of several Taft-type linear free energy relationships indicates that the change in steric environment which a substituent experiences when it is moved from the acyl part to the alkyl part of an amide is quantitatively similar to the change in steric environment experienced by the same substituent in moving from the acyl to the alkyl portion of an ester. Evidence is also presented that the change in six-number makes the greatest contribution to the change in steric environment.

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