Kinetics of reactions in solutions under pressure. 49. Chlorine kinetic isotope effects in the methylation of pyridine and 2,6-lutidine

1979 ◽  
Vol 44 (5) ◽  
pp. 889-891 ◽  
Author(s):  
Le Noble W. J. ◽  
Arnold R. Miller
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Kinetics Of

Kinetics of the reduction of nicotinonitrile cations by 1,4-dihydronicotinamides

1985 ◽  
Vol 63 (6) ◽  
pp. 1245-1249 ◽  
Author(s):  
John W. Bunting ◽  
John C. Brewer
Keyword(s):  
Ionic Strength ◽  
Transition State ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Spectral Studies ◽  
Close Correspondence ◽  
Charge Generation ◽  
Kinetic Isotope ◽  
Hammett Σ Constants ◽  
Kinetics Of

The rates of reduction of a series of 1-(Z-benzyl)nicotinonitrile cations by a series of 1-(X-benzyl)-1,4-dihydronicotinamides have been studied at 25 °C in 20% CH3CN – 80% H2O (pH 7.0 (5 mM phosphate), ionic strength 1.0 (KCl)). Spectral studies indicate the formation of 1,4-dihydronicotinonitrile products, without the formation of the isomeric 1,2-dihydro- or 1,6-dihydro-nicotinamide intermediates. Second-order rate constants (k2) for these reductions are closely correlated with the Hammett σ constants for X and Z. Thus, for X = H, log k2 = 0.63σz − 1.05, while for Z = 4-CN, log k2 = −0.64σx − 0.65. The close correspondence between these ρx and ρz values indicates that charge neutralization on the nicotinonitrile cation exactly balances charge generation on the nicotinamide cation product in the rate-determining transition state. Thus the migrating hydrogen species is electrically neutral in the rate-determining transition state, which contrasts with the hydridic transition states previously reported in the reduction of isoquinolinium cations by 1,4-dihydronicotinamides. When 1-benzyl-4,4-dideuterio-1,4-dihydronicotinamide is used as the reductant, primary kinetic isotope effects of 3.0 and 2.7 are observed for the reduction of the 1-methylnicotinonitrile and 1-(4-cyanobenzyl)-nicotinonitrile cations, respectively. These data are evaluated in terms of the various mechanistic possibilities for hydride transfer.

The pH dependence of xanthine oxidase catalysis in basic solution

1980 ◽  
Vol 58 (5) ◽  
pp. 394-398 ◽  
Author(s):  
John W. Bunting ◽  
Keith R. Laderoute ◽  
Donald J. Norris
Keyword(s):  
Xanthine Oxidase ◽  
Isotope Effects ◽  
Ph Dependence ◽  
Kinetic Isotope Effects ◽  
Similar Rate ◽  
Basic Solution ◽  
Kinetic Isotope ◽  
Steady State Kinetics ◽  
Pyridinium Cations ◽  
Kinetics Of

The steady-state kinetics of the oxidation of the following six heteroaromatic substrates by xanthine oxidase have been investigated over the range pH 9.0–11.1 at 25 °C, ionic strength 0.1: 1-methylquinolinium, 6-methoxy-1-methylquinolinium, 1-methylnicotinamide, 3-acetyl-1-methylpyridinium, and 1-(4-methoxyphenyl)pyridinium cations and 1-methylnicotinate zwitterion. For the first four of these species, kc and Km were evaluated as a function of pH while only kc/Km was accessible in the latter two cases. Where available, kc is pH independent, whereas plots of log (kc/Km) vs. pH are linear with slopes in the range 0.54–1.17.The rates of enzymic oxidation of the 1-methylquinolinium cation and its 2-deuterio derivative were investigated and kinetic isotope effects were calculated at pH 9.8 and 10.6: kcH/kcD = 1.7 and KmH/KmD = 0.4 at each pH. Detailed comparisons of the oxidation of heteroaromatic cations and xanthine-derived substrates indicate that similar rate-determining steps control the enzymic oxidations of these two classes of substrate.

The thermally induced rearrangements of 2-vinyloxirane

1976 ◽  
Vol 54 (21) ◽  
pp. 3364-3376 ◽  
Author(s):  
Robert J. Crawford ◽  
Stuart B. Lutener ◽  
Robert D. Cockcroft
Keyword(s):  
Carbon Monoxide ◽  
Gas Phase ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Thermally Induced ◽  
Rate Determining Step ◽  
Kinetic Isotope ◽  
Carbonyl Ylide ◽  
Structural Isomerization ◽  
Kinetics Of

The kinetics of the gas phase thermolysis of 2-vinyloxirane (4) have been studied over the temperature range 270–310 °C. The racemization of chiral 4 occurs six times faster than the structural isomerization to 2,3-dihydrofuran, (E)- and (Z)-2-butenal, and 3-butenal. The butenals undergo a slow thermolysis to propene and carbon monoxide. cis-Deuterio- and trans-3-deuterio-vinyloxirane have been synthesized and their interconversion is slow. Deuterium kinetic isotope effects on mono- and dideuterio-4 suggest that for the formation of the butenals the rate determining step involves rupture of the oxirane C—O bond. The dihydrofuran is produced by thermolysis of the oxirane C—C bond. The preferred mechanistic interpretation is that a carbon–oxygen diradical serves as an intermediate for butenal formation, and that a carbonyl-ylide is involved in the formation of the dihydrofuran.The relative rates, at 307.4 °C, of cis–trans-5-isomerization:dihydrofuran formation:racemization: butenal formation for 3-deuterio-2-vinyloxirane are 1.0:0.88:40.2:5.94, respectively.

Concerted Pathway to the Mechanism of the Anilinolysis of Bis(N,N-diethylamino)phosphinic Chloride in Acetonitrile

2017 ◽  
Vol 70 (1) ◽  
pp. 101 ◽  
Author(s):  
Hasi Rani Barai
Keyword(s):  
Nucleophilic Substitution ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Substituted Anilines ◽  
Substitution Reactions ◽  
Nucleophilic Substitution Reactions ◽  
Kinetic Isotope ◽  
Kd Values ◽  
Kinetics Of

The kinetics of the nucleophilic substitution reactions of bis(N,N-diethylamino)phosphinic chloride with substituted anilines (XC6H4NH2) and deuterated anilines (XC6H4ND2) are investigated in MeCN at 65.0°C. The deuterium kinetic isotope effects (DKIEs) are secondary inverse (kH/kD < 1: 0.706–0.947) and the magnitudes of the secondary inverse DKIEs (kH/kD) increase constantly as the nucleophiles are changed from weakly basic to strongly basic anilines. The magnitudes of the selectivity parameters are ρX(H) = –6.34, and βX(H) = 2.24 with substituted anilines and ρX(D) = –6.13 and βX(D) = 2.17 with deuterated anilines. A concerted SN2 mechanism involving predominant backside attack is proposed based on the kH/kD values with substituent X.

A Combined Computational–Experimental Study of the Kinetics of Intramolecular Diels–Alder Reactions in a Series of 1,3,8-Nonatrienes

2015 ◽  
Vol 68 (2) ◽  
pp. 230 ◽  
Author(s):  
William J. Lording ◽  
Alan D. Payne ◽  
Tory N. Cayzer ◽  
Michael S. Sherburn ◽  
Michael N. Paddon-Row
Keyword(s):  
Density Functional ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Kinetic Isotope Effects ◽  
Alder Reaction ◽  
Diels Alder ◽  
Functional Theory ◽  
Kinetic Isotope ◽  
Diels Alder Reaction ◽  
Kinetics Of

Activation enthalpies for a series of five 1,3,8-nonatriene intramolecular Diels–Alder (IMDA) reactions involving substrates 1–5 have been determined experimentally and Singleton’s natural abundance method has been employed to determine kinetic isotope effects in the IMDA reaction of fumarate 3. The activation enthalpies for the IMDA reactions of the systems possessing a –CH2OCH2– diene/dienophile tether are significantly smaller than their counterparts possessing the –CH2OC(=O)– tether. The experimental activation enthalpies have been used to benchmark computed values from four model chemistries, namely two density functional theory functionals, B3LYP and M06-2X, and two generally very accurate composite ab initio wave function methods, CBS-QB3 and G4(MP2). G4(MP2) outperformed the computationally more expensive CBS-QB3 method, but the vastly cheaper M06-2X/6-31G(d)//B3LYP/6-31G(d) method was sufficiently accurate to be the recommended method of choice for calculating activation parameters. Experimental 2H kinetic isotope effects for the IMDA reaction of fumarate 3 confirmed the computational predictions that this Diels–Alder reaction is concerted but asynchronous.

scholarly journals How does tautomerization affect the excited-state dynamics of an amino acid-derivatized corrole?

2021 ◽  
Author(s):  
John A. Clark ◽  
Rafał Orłowski ◽  
James B. Derr ◽  
Eli M. Espinoza ◽  
Daniel T. Gryko ◽  
...  
Keyword(s):  
Excited State ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Important Class ◽  
Singlet Excited State ◽  
Free Base ◽  
Excited State Dynamics ◽  
Kinetic Isotope ◽  
Kinetics Of ◽  
Photoinduced Processes

AbstractIn the first two decades of the XXI century, corroles have emerged as an important class of porphyrinoids for photonics and biomedical photonics. In comparison with porphyrins, corroles have lower molecular symmetry and higher electron density, which leads to uniquely complementary properties. In macrocycles of free-base corroles, for example, three protons are distributed among four pyrrole nitrogens. It results in distinct tautomers that have different thermodynamic energies. Herein, we focus on the excited-state dynamics of a corrole modified with l-phenylalanine. The tautomerization in the singlet-excited state occurs in the timescales of about 10–100 picoseconds and exhibits substantial kinetic isotope effects. It, however, does not discernably affect nanosecond deactivation of the photoexcited corrole and its basic photophysics. Nevertheless, this excited-state tautomerization dynamics can strongly affect photoinduced processes with comparable or shorter timescales, considering the 100-meV energy differences between the tautomers in the excited state. The effects on the kinetics of charge transfer and energy transfer, initiated prior to reaching the equilibrium thermalization of the excited-state tautomer population, can be indeed substantial. Such considerations are crucially important in the design of systems for artificial photosynthesis and other forms of energy conversion and charge transduction.

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