Carbanion reactivity — σ-adduct formation and elimination in the reactions of the carbanion from bis(phenylsulfonyl)methane with 4-nitrobenzofurazan derivatives

2008 ◽  
Vol 86 (3) ◽  
pp. 225-229 ◽  
Author(s):  
Basim H.M. Asghar ◽  
Michael R Crampton ◽  
Chukwuemeka Isanbor
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Intrinsic Rate ◽  
Adduct Formation ◽  
Nmr Studies ◽  
H Nmr ◽  
A Value ◽  
Elimination Reactions ◽  
Intrinsic Rate Constant

1H NMR studies in [2H6]-DMSO show that the carbanion 4 from bis(phenylsulfonyl)methane reacts with 4,6-dinitrobenzofuroxan to yield a σ-adduct that undergoes base-catalysed elimination to yield an alkene derivative. Rate constants, measured spectrophotometrically, are reported for the corresponding reactions in methanol of 4 with 4-nitrobenzofurazan and some derivatives that give adducts at the 5-position. The intrinsic rate constant, ko, for this process has a value of 1.5 ± 0.5. The 5-adducts undergo methoxide-catalysed elimination of phenylsulfinic acid to yield alkene derivatives and rate constants for this process are reported.Key words: carbanions, 4-nitrobenzofurazan, σ-adducts, elimination reactions.

scholarly journals A Two-part Approach to the Determination of Intrinsic Rate Constants of an Alpha-amylase Catalysed Reaction

2020 ◽  
pp. 8-21
Author(s):  
Ikechukwu I. Udema
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Catalytic Efficiency ◽  
Intrinsic Rate ◽  
Product Formation ◽  
Intermolecular Potential ◽  
Diffusion Controlled ◽  
Quantitative Results ◽  
Intrinsic Rate Constant

Background: There is a need for equations with which to calculate the intrinsic rate constants that can further characterise enzyme catalysed reactions despite what seems to be conventional differences in methodology in the literature. Methods: Theoretical, experimental (Bernfeld method), and computational methods. Objectives: 1) To derive an alternative intrinsic rate constant equations consistent with their dimension, 2) derive electrostatic intermolecular potential energy equation, (xe), 3) calculate the intrinsic rate constants for forward (k1) and reverse (k2) reactions, and 4) define the dependence or otherwise of kinetic constants on diffusion and deduce the catalytic efficiency. Results and Discussion: The ultimate quantitative results were ~ 64.69 ±  0.49 exp (+3)/ min (k2) (and kd (s) = ~ 60.66 exp (+3)/ min), ~ 1594.48 ± 11.99 exp (+3) exp (+3) L/mol.min (k1) (and ka (s) = ~1482.47 exp (+3) L/mol.min), ~ 58.00 ± 10.83 exp (+3) /min, the apparent rate constant for reverse reaction (kb), and ~ 75.83 ± 10.83 exp (+3) /min, the rate constant for product formation (k3). The catalytic efficiency was: 3.025 exp (+ 9) L / mol.     Conclusion: The relevant equations were derived. Based on the derived equations the intrinsic rate constants can be calculated. Since k3 is > kb, then k3 is diffusion controlled and it appears that the enzyme has reached kinetic perfection. The evaluation of rate constants either from the perspective of diffusion dependency or independency cannot be valid without Avogadro number.

A magnetically aligning lyotropic mesophase with a clay inclusion

1985 ◽  
Vol 63 (10) ◽  
pp. 2628-2632 ◽  
Author(s):  
M. A. Desando ◽  
L. W. Reeves
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Ternary Phase ◽  
Type I ◽  
Slow Process ◽  
Phase Relaxation ◽  
H Nmr ◽  
Tenfold Increase

The inclusion of clay (bentonite) (ca. 0.08–0.64 wt.%) in the lyotropic mesophase formed by potassium dodecanoate + KCl + 2H2O has been observed by 2H nmr not to alter the type I CM character of the phase. Relaxation of the mesophase director has been analyzed in terms of two processes over a range of 2H2O concentrations. A slow process with rate constants of ca. 2 × 10−4 − 8 × 10−4 s−1 exists for the phase with clay over 2H2O concentrations of 63.9–65.9 wt.%. A tenfold increase in the rate constant with an increase in the 2H2O content from 62.5 to 65.5% was observed for the ternary phase at 302 K.

scholarly journals Absolute rate constant and O(<sup>3</sup>P) yield for the O(<sup>1</sup>D)+N<sub>2</sub>O reaction in the temperature range 227 K to 719 K

2008 ◽  
Vol 8 (20) ◽  
pp. 6261-6272 ◽  
Author(s):  
S. Vranckx ◽  
J. Peeters ◽  
S. A. Carl
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Room Temperature ◽  
Marked Decrease ◽  
Quantum Yields ◽  
Absolute Rate ◽  
Temperature Range ◽  
A Value ◽  
Relative Quantum ◽  
Absolute Rate Constant

Abstract. The absolute rate constant for the reaction that is the major source of stratospheric NOx, O(1D)+N2O → products, has been determined in the temperature range 227 K to 719 K, and, in the temperature range 248 K to 600 K, the fraction of the reaction that yields O(3P). Both the rate constants and product yields were determined using a recently-developed chemiluminescence technique for monitoring O(1D) that allows for higher precision determinations for both rate constants, and, particularly, O(3P) yields, than do other methods. We found the rate constant, kR1, to be essentially independent of temperature between 400 K and 227 K, having a value of (1.37±0.11)×10−10 cm3 s−1, and for temperatures greater than 450 K a marked decrease in rate constant was observed, with a rate constant of only (0.94±0.11)×10−10 cm3 s−1 at 719 K. The rate constants determined over the 227 K–400 K range show very low scatter and are significantly greater, by 20% at room temperature and 15% at 227 K, than the current recommended values. The fraction of O(3P) produced in this reaction was determined to be 0.002±0.002 at 250 K rising steadily to 0.010±0.004 at 600 K, thus the channel producing O(3P) can be entirely neglected in atmospheric kinetic modeling calculations. A further result of this study is an expression of the relative quantum yields as a function of temperature for the chemiluminescence reactions (kCL1)C2H + O(1D) → CH(A) + CO and (kCL2)C2H + O(3P) → CH(A) + CO, both followed by CH(A) → CH(X) + hν, as kCL1(T)/kCL2(T)=(32.8T−3050)/(6.29T+398).

scholarly journals The kinetics of oxygen exchange between the sulfite ion and water

1970 ◽  
Vol 48 (13) ◽  
pp. 2035-2041 ◽  
Author(s):  
R. H. Betts ◽  
R. H. Voss
Keyword(s):  
Aqueous Solution ◽  
Ionic Strength ◽  
Rate Constant ◽  
Rate Constants ◽  
Time Rate ◽  
A Value ◽  
First Time ◽  
Kinetics Of ◽  
Sulfite Ion ◽  
Gross Rate

Oxygen of mass 18 was used as a stable tracer to measure the rate of exchange between the sulfite ion and water as a function of pH and total sulfite concentration. A value for the rate constant of hydration of SO2 in aqueous solution was determined. The gross rate constants k1 and k−1 for the overall reaction[Formula: see text]at 24.7 °C and ionic strength = 0.9 were evaluated from exchange results to be [Formula: see text]Also, for the first time, rate constants for the pyrosulfite equilibrium[Formula: see text]Were obtained[Formula: see text]at 24.7 °C and ionic strength = 0.9

Thermal effects in flash photolysis with special reference to Br atom recombination

1968 ◽  
Vol 46 (20) ◽  
pp. 3229-3234 ◽  
Author(s):  
George Burns
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Thermal Effects ◽  
Reaction Rate ◽  
Flash Photolysis ◽  
Reaction Rate Constants ◽  
A Value ◽  
Recombination Rate Constant ◽  
Reaction Vessels

Thermal effects, which accompany flash photolyses, are known to interfere with the determination of reaction rate constants. There are two approximate models currently being used in literature to estimate the magnitude of these effects (1, 8). The first model (1) is the more widely accepted. It is based on the assumption that thermal effects are due to the cooling of reacting gas at the walls of the reaction vessel. The second model (8) is based on the assumption that thermal effects are due to nonuniformity in the concentrations of free radicals produced in flash photolysis; it neglects the heat exchange at the wall of the reaction vessel.It is shown that the second model can be used to calculate the magnitude of thermal effects in reaction vessels of reasonable length. The model was applied to calculate [Formula: see text], the rate constant for the reaction 2Br + Br2 → 2Br2. The value of [Formula: see text], is found to be very sensitive to the choice of model for thermal effects. At room temperature the most reasonable value of [Formula: see text], using the second model, is (4.3 ± 1.3) × 1010 l2 mole−2 s−1. This value agrees very well with independent determinations of [Formula: see text] using a stationary photochemical technique. The first model for treatment of thermal effects (1) was used previously to show that such effects do not influence the measured rates of chemical reactions, and calculations of rate constants using this model have not usually been attempted. In one case (5), however, the first model (1) for thermal effects was employed to calculate a value for [Formula: see text] which was found to be six times larger than our value. Consequently, the second model (8) appears to be a better approximation for quantitative evaluation of thermal effects.Using the raw data (8) and [Formula: see text] = 43 × 109 l2 mole−2 s−1, the value of kAr, the recombination rate constant of Br atoms in excess of argon, was found to be (3.0 ± 0.2) × 109 l2 mole−2 s−1, which agrees well with data available in the literature.

THE LIFETIME OF THE STATE OF N2

1965 ◽  
Vol 43 (2) ◽  
pp. 369-374 ◽  
Author(s):  
L. F. Phillips
Keyword(s):  
Decay Rate ◽  
Rate Constant ◽  
Rate Constants ◽  
Blue Emission ◽  
Order Rate Constant ◽  
The State ◽  
Active Nitrogen ◽  
First Order ◽  
A Value ◽  
Mean Lifetime

The decay of the blue emission from the active nitrogen – iodine flame has been measured at iodine pressures down to 1.4 × 10−4 torr. Extrapolation of the decay rate to zero iodine pressure yields a value of 0.89 ± 0.41 s−1 for the first-order rate constant in absence of iodine, corresponding to a mean lifetime of 1.1 s for the [Formula: see text] state of N2. The rate constants for the reactions[Formula: see text]and[Formula: see text]are (2.6 ± 0.3) × 10−11 exp (−68 ± 34/RT) and (8.3 ± 1.2) × 10−14 cm3 molecule−1 s−1 respectively.

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