Studies on the decomposition of tetra-alkylammonium salts in solution. Part III: Interpretation of Hammett correlations

1970 ◽  
Vol 48 (12) ◽  
pp. 1865-1868 ◽  
Author(s):  
E. C. F. Ko ◽  
K. T. Leffek
Keyword(s):  
Free Energy ◽  
Nitrogen Atom ◽  
Phenyl Group ◽  
Acetone Solution ◽  
Reaction Site ◽  
Decomposition Reactions ◽  
Linear Plot ◽  
Alkylammonium Salts ◽  
Alkylammonium Halides

Hammett free energy correlations are reported for the decomposition reactions of tetra-alkylammonium halides in chloroform and acetone solution. All the salts contained a substituted benzyl group attached to the nitrogen atom and decomposed to yield a benzyl iodide and dimethylaniline as the only products.The curved Hammett plots for para-substituted benzyl compounds are compared to the linear plot found previously for a series of salts each containing a para-substituted phenyl group, and it is concluded that curved Hammett plots cannot be used as evidence for a change of mechanism, unless direct conjugative effects between substituent and reaction site are absent.

Studies on the decomposition of tetra-alkylammonium salts in solution. Part II. Dependence of the activation parameters on the structure of the substrate

1969 ◽  
Vol 47 (20) ◽  
pp. 3725-3728 ◽  
Author(s):  
J. T. Burns ◽  
K. T. Leffek
Keyword(s):  
Free Energy ◽  
Nitrogen Atom ◽  
Tertiary Amine ◽  
Chloroform Solution ◽  
Activation Parameters ◽  
Decomposition Reaction ◽  
Energy Correlation ◽  
Entropy Of Activation ◽  
Alkylammonium Salts ◽  
Enthalpy And Entropy

The enthalpy and entropy of activation for the decomposition reaction of seven tetra-alkylammonium iodides in chloroform solution have been measured. All the salts contained the benzyl group attached to the nitrogen atom and decomposed to yield benzyl iodide and a tertiary amine as the only products.A Hammett free energy correlation is made and used to deduce the nature of the transition state, and a rationalization of the variation of the enthalpy and entropy of activation with the structure of the substrate is given.

scholarly journals Basicity of N5 in semiquinone enhances the rate of respiratory electron outflow inShewanella oneidensisMR-1

2019 ◽  
Author(s):  
Yoshihide Tokunou ◽  
Keisuke Saito ◽  
Ryo Hasegawa ◽  
Kenneth H. Nealson ◽  
Kazuhito Hashimoto ◽  
...  
Keyword(s):  
Free Energy ◽  
Electron Transport ◽  
Nitrogen Atom ◽  
Outer Membrane ◽  
Diffusion Constant ◽  
Shewanella Oneidensis ◽  
Molecular Structures ◽  
Redox Potentials ◽  
Transport Reaction ◽  
Extracellular Electron Transport

AbstractExtracellular electron transport (EET) occurs in environmental iron-reducing bacteria and is mediated by an outer membrane multi-heme cytochrome complex (Cyts). It has critical implications for global mineral cycling and electrochemical microbial catalysis. The rate of EET mediated by multiple heme redox centers significantly increases in the presence of flavins and quinones. Their electron free energy does not entirely account for the fact that differential effects on EET rate enhancement vary significantly by factors ≥100. Here, we report on whole-cell electrochemical analysis ofShewanella oneidensisMR-1 using six flavin analogs and four quinones. We demonstrated that protonation of the nitrogen atom at position 5 (N5) of the isoalloxazine ring is essential for electron outflow acceleration as a bound non-covalent cofactor of Cyts. EET mediated by Cyts was accelerated at a rate dependent on pKa(N5). The EET rate largely decreased in response to the addition of deuterated water (D2O), while low concentration of D2O (4 %) had little impact on electron free energy difference of the heme and non-covalent bound cofactors, strongly suggesting that the protonation of N5 limits the rate of EET. Our findings directly link EET kinetics to proton transport reaction via N5 and provide a basis for the development of novel strategies for controlling EET-associated biological reactions.Significance statementThe potential of various small molecules such as flavins and quinones to enhance the rate of extracellular electron transport (EET) has been exploited to develop environmental energy conversion systems. Flavins and quinones have similar molecular structures but their abilities to enhance EET vary by >100× inShewanella oneidensisMR-1. These large differences are inconsistent with conventional models, which rely on redox potentials or diffusion constant of shuttling electron mediators. In this study, we demonstrated that the basicity of the nitrogen atom of the isoalloxazine ring (N5) enhances the rate of electron outflow when a flavin or quinone is a non-covalent cofactor ofS. oneidensisMR-1 outer membranec-type cytochromes.

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.

Free-energy relationships in coordination chemistry. II. Requirements for linear relationships

1970 ◽  
Vol 48 (16) ◽  
pp. 2565-2573 ◽  
Author(s):  
E. Nieboer ◽  
W. A. E. McBryde
Keyword(s):  
Free Energy ◽  
Strong Interactions ◽  
Thermodynamic Quantities ◽  
Reaction Site ◽  
Independent Variables ◽  
Linear Free Energy ◽  
Linear Relationships ◽  
In Series ◽  
Energy Relationships ◽  
Equilibrium Relationships

This paper discusses factors predisposing to linear free energy relationships among families of metal complexes. It is postulated that changes occurring at a reaction site in a test series of reactions and the corresponding changes in a reference series have their origins in the same independent variables. Linearity is seen to be favored when changes in the reaction site or in ligand substituents are small, and in the absence of strong interactions with the solvent. In addition to such considerations of a molecular sort, a number of relationships among the thermodynamic quantities ΔH0, ΔS0, and ΔG0 which have been identified as having a significant influence on rate and equilibrium relationships in series of organic reactions are discussed in terms of their effect on metal–ligand systems.

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.

Dipolar and calorimetric study of the complexes between N,N-dimethyl-N′-phenylformamidines and phenols

1976 ◽  
Vol 54 (4) ◽  
pp. 610-616 ◽  
Author(s):  
Alfred F. Foubert ◽  
Pierre L. Huyskens
Keyword(s):  
Hydrogen Bond ◽  
Nitrogen Atom ◽  
Electron Pair ◽  
Dipole Moments ◽  
Phenyl Group ◽  
Ion Pair ◽  
Proton Donor ◽  
Pair Type ◽  
Calorimetric Study ◽  
Imino Nitrogen

The dipole moments µb of N,N-dimethyl-N′-phenylformamidine and its 4-methylphenyl and 4-chorophenyl derivatives and the dipole moments µab of some 20 complexes of these bases with phenols were determined in cyclohexane at 298 K. Assuming the additivity of the bond moments, the angles αb between µb and the axis C1C4 phenyl group were computed for the three bases. Dipole increments [Formula: see text] were then computed assuming the hydrogen bond involved the electron pair of the sp2 hybridized imino nitrogen atom. The variation of the Δµ computed in this way with the complexation enthalpy ΔHab is described by the same curve as that for the systems phenols–anilines and phenols–pyridines. This is not the case when other structures are chosen for computing Δµ and this provides evidence for the 'imino' structure of the complexes. For a given amidine, the dipole increment increases when the proton donor becomes more acidic. The derivative d Δµ/dpKa here is of the order of −0.5 D per pKa unit whereas this value is only −0.2 for the pyridines. The absolute values of Δµ are also greater for the amidines. This can be ascribed in part to a higher proportion of H-bonds of the ion pair type [Formula: see text] when the amidine is complexed by the same phenol as the pyridines.

Infrared Absorption of the Carbonyl Group of Semicarbazides, Semicarbazones, and Pyrazolecarboxamides

1968 ◽  
Vol 22 (3) ◽  
pp. 167-169 ◽  
Author(s):  
Tze Seng Wang
Keyword(s):  
Nitrogen Atom ◽  
Carbonyl Group ◽  
Infrared Absorption ◽  
Phenyl Group ◽  
Frequency Region ◽  
The Third ◽  
Alkyl Groups ◽  
Carbonyl Absorption

The carbonyl frequency in semicarbazides, semicarbazones, and pyrazolecarboxamides is higher than that in ureas. A phenyl group attached to the third nitrogen atom of semicarbazides lowers the carbonyl frequency. A phenyl group substituted on the first nitrogen atom shifts the carbonyl absorption in semicarbazides to a higher frequency region than do alkyl groups.

scholarly journals Electrofugality of Some Ferrocenylphenylmethyl Cations

2019 ◽  
Vol 92 (2) ◽  
pp. 307-313
Author(s):  
Sandra Jurić ◽  
Marijan Marijan ◽  
Olga Kronja
Keyword(s):  
Free Energy ◽  
Phenyl Ring ◽  
Positive Charge ◽  
Narrow Range ◽  
Phenyl Group ◽  
Linear Free Energy Relationship ◽  
Methyl Ethyl ◽  
Linear Free Energy ◽  
Ferrocenyl Group ◽  
Complete Set

The electrofugality scale has been extended with new substituted ferrocenylphenylmethyl cations 1-4. Ef values were determined by applying the linear free energy relationship (LFER): log k = sf (Ef + Nf). Due to ability of the ferrocene moiety to efficiently stabilize the positive charge, ferrocenylphenylmethyl cations constitute a group of very powerful electrofuges (Ef > 1). Impact of the phenyl group in ferrocenylphenylmethyl derivatives on stabilization of the positive charge is considerably leveled by the ferrocenyl group, so the rate effect of the alkyl substituents (methyl, ethyl and tert-butyl) on the phenyl ring is suppressed, causing narrow range of Ef parameters. Lack of breakdown of Hammett-Brown plot if the rates for the complete set of substrates 1–5 have been correlated, indicates that the ferrocenyl group in α-position diminishes the stabilizing effects of electron-donating substituents as well.

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