THE UNIMOLECULAR DECOMPOSITION OF METHYL CHLORIDE

1965 ◽  
Vol 43 (11) ◽  
pp. 3052-3056 ◽  
Author(s):  
W. Forst ◽  
P. St. Laurent
Keyword(s):  
Rate Constant ◽  
Level Density ◽  
Methyl Chloride ◽  
Good Deal ◽  
Order Rate Constant ◽  
Unimolecular Decomposition ◽  
Calculated Rate ◽  
Quantum Version ◽  
Experimental Activation Energy ◽  
Made In

The second-order rate constant for the unimolecular decomposition of methyl chloride[Formula: see text]has been calculated on a computer by the quantum version of the Marcus–Rice theory assuming no active rotations and using the experimental activation energy. With a harmonic energy level density count the calculated rate constant is 32 times smaller than the experimental value. When correction for anharmonicity is applied, the agreement is somewhat improved but the calculated rate constant is still some 20 times too small. These results are discussed in the light of the assumptions made in the course of the calculations. It is concluded that the quantum statistical collision theory, to which the Marcus–Rice theory reduces at low pressure, is a good deal more successful than Slater's, which is in error by a factor of 105–106.

Unimolecular decomposition of methyl chloride. II. Some refinements of the calculations

1967 ◽  
Vol 45 (24) ◽  
pp. 3169-3176 ◽  
Author(s):  
W. Forst ◽  
P. St. Laurent
Keyword(s):  
Angular Momentum ◽  
Rate Constant ◽  
Degrees Of Freedom ◽  
Methyl Chloride ◽  
Computational Procedure ◽  
Intramolecular Energy Transfer ◽  
Collision Theory ◽  
Unimolecular Decomposition ◽  
Rational Argument ◽  
Quantum Version

The quantum version of the statistical collision theory is applied to the unimolecular decomposition of methyl chloride in the second-order region using an improved computational procedure and a more realistic physical model. An attempt is made to determine active degrees of freedom, i.e. degrees of freedom participating in intramolecular energy transfer, by rational argument. These considerations point to at least one overall rotation as active, in addition to all nine vibrations as active. Conservation of angular momentum is explicitly considered in the case of one active rotation and an appropriate correction factor is included in the calculated rate constant, as is a correction for anharmonicity. The theoretical rate constant so computed is within less than a factor of two of the experimental value.

The homogeneous decomposition reactions of gaseous formic acid

1960 ◽  
Vol 255 (1283) ◽  
pp. 444-455 ◽  
Keyword(s):  
Formic Acid ◽  
Kinetic Parameters ◽  
Rate Constant ◽  
Ion Pairs ◽  
Order Rate Constant ◽  
Second Order ◽  
Unimolecular Decomposition ◽  
Order Component ◽  
First Order ◽  
Homogeneous Decomposition

By use of reaction vessels with specially treated surfaces the homogeneous decomposition of formic acid has been studied kinetically in the range 436 to 532°C. Neither of the two simultaneous reactions ( a ) HCOOH = CO 2 + H 2 , ( b ) HCOOH = CO + H 2 O, is retarded by the usual inhibitors of chain processes. Each appears to be molecular. Reaction ( a ) is of the first order in the range 3 to 650 mm, the first-order rate constant being given by k CO 2 = 10 4⋅8 exp (–30600/ RT )s -1 . It is suggested tentatively that the abnormal kinetic parameters might be explained by regarding the reaction as a decarboxylation of (H + ) (HCOO¯) ion pairs present in minute concentration. Reaction ( b ) shows a pressure dependence most simply explained by a superposition of a predominant second-order component with a small first-order component. The most satisfactory interpretation of the second-order reaction is that it represents the unimolecular decomposition of dimer molecules, known to be present in formic-acid vapour. On this basis the rate constant is given by k CO dimer = 10 13⋅58 exp (–42600/ RT )s -1 , the kinetic parameters thus being in the normal range. The various alternative interpretations are discussed.

THE THERMAL DECOMPOSITION OF ETHANE: PART II. THE UNIMOLECULAR DECOMPOSITION OF THE ETHANE MOLECULE AND THE ETHYL RADICAL

1966 ◽  
Vol 44 (20) ◽  
pp. 2357-2367 ◽  
Author(s):  
M. C. Lin ◽  
M. H. Back
Keyword(s):  
High Pressure ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Methyl Radicals ◽  
Unimolecular Decomposition ◽  
First Order ◽  
Order Rate ◽  
Ethyl Radical ◽  
Lower Temperature ◽  
Ethyl Radicals

The rate of the elementary dissociation of ethane into two methyl radicals has been measured in its pressure-dependent region at temperatures from 913–999 °K and at pressures from 1–200 mm. The high-pressure first-order rate constant obtained by extrapolation was in agreement with that obtained at lower temperatures,[Formula: see text]Comparison with calculated Kassel curves showed that the best fit of the data was obtained with the Kassel parameter s = 12 ± 1. The high-pressure first-order rate constant for the decomposition of the ethyl radical was obtained by extrapolation of the data reported in Part I, assuming the rate constant for combination of ethyl radicals is independent of temperature.[Formula: see text]From the measured constant for the dissociation of ethane, the rate constant for the combination of methyl radicals was calculated and compared with the values measured in a lower temperature region. Differences in the values of the rate constants and in the shapes of the unimolecular falloff curves are discussed.

Kinetics of the Anation Reaction of Nickel(II) and 1,10-Phenanthroline in Ethanol

1972 ◽  
Vol 50 (23) ◽  
pp. 3861-3865 ◽  
Author(s):  
M. L. Sanduja ◽  
W. MacF. Smith
Keyword(s):  
Rate Constant ◽  
Sodium Perchlorate ◽  
Order Rate Constant ◽  
Stopped Flow ◽  
Tetrabutyl Ammonium ◽  
Kinetics Of Formation ◽  
Kinetics Of ◽  
Nickel Perchlorate ◽  
Anation Reaction ◽  
Made In

The kinetics of formation of the monophenanthroline complex of nickel(II) in ethanol has been studied using stopped-flow methods over the temperature range 7 to 35 °C. Tetrabutyl ammonium perchlorale in concentration 0.044 M does not affect the rate appreciably, sodium perchlorate at the same concentration depresses the rate significantly. Most measurements were made in the absence of electrolytes other than nickel perchlorate and a trace of perchloric acid. The second order rate constant is not significantly dependent on the nickel(II) concentration over a four-fold change in value indicating that the concentration of encounter pairs is small relative to the concentration of the free reactants. The rate constant at 25 °C (31 × 103 M−1 s−1)is consistent with a dissociative interchange mechanism and the rate constant for ethanol exchange on nickel. However, the value of ΔH≠ for the overall reaction (15.9 ± 1.0 kcal mol−1) is about 5 kcal mol−1 higher than that reported for ethanol exchange.

Development of Sustained Release Multi-Component Microparticulate System of Diclofenac Sodium and Tizanidine Hydrochloride

1970 ◽  
Vol 1 (1) ◽  
pp. 97-105
Author(s):  
Kamlesh Dashora ◽  
Shailendra Saraf ◽  
Swarnalata Saraf
Keyword(s):  
Particle Size ◽  
Sustained Release ◽  
Cellulose Acetate ◽  
Rate Constant ◽  
Diclofenac Sodium ◽  
Order Rate Constant ◽  
Anomalous Transport ◽  
First Order ◽  
Sem Study ◽  
Transport Type

Sustained released tablets of diclofenac sodium (DIC) and tizanidine hydrochloride (TIZ) were prepared by using different proportions of cellulose acetate (CA) as the retardant material. Nine formulations of tablets having different proportion of microparticles developed by varied proportions of polymer: drug ratio ‘’i.e.’’; 1:9 -1:3 for DIC and 1:1 – 3:1 for TIZ. Each tablet contained equivalent to 100 mg of DIC and 6mg of TIZ. The prepared microparticles were white, free flowing and spherical in shape (SEM study), with  the particle size varying from 78.8±1.94 to 103.33±1.28 µm and 175.92± 9.82 to 194.94±14.28µm for DIC  and TIZ, respectively.  The first order rate constant K1 of formulations were found to be in the range of  K1 = 0.117-0.272 and 0.083- 0.189 %hr-1for DIC and TIZ, respectively. The value of exponent coefficient (n) was found to be in the range of 0.6328-0.9412  and 0.8589-1.1954 for DIC and TIZ respectively indicates anomalous  to  non anomalous transport type of diffusions among different formulations

scholarly journals Alkylation of glyceraldehyde-3-phosphate dehydrogenase with haloacetylphosphonates. An unusual pH-dependence

1991 ◽  
Vol 275 (3) ◽  
pp. 767-773 ◽  
Author(s):  
Y K Li ◽  
J Boggaram ◽  
L D Byers
Keyword(s):  
Isotope Effect ◽  
Rate Constant ◽  
Ph Dependence ◽  
Thiol Group ◽  
Order Rate Constant ◽  
Acidic Group ◽  
Irreversible Inhibitors ◽  
Effects Of Ph ◽  
Solvent Isotope ◽  
Bell Shaped Curve

Two new alkylating reagents, chloro- and bromo-acetylphosphonate, were found to be very effective thiol-blocking reagents. The pH-dependence of the reaction of BAP with 2,4-dinitrothiophenol (25 degrees C, I 0.5) shows a tailing bell-shaped curve (with a plateau at high pH) characteristic of two ionizing groups: the thiol group (pKa 3.2) and the phosphonate group (pKa2 4.6). The rate constant for the reaction of the monoanionic inhibitor with dinitrothiophenolate (k2 = 7 M-1.s-1) is 120 times larger than that of the dianionic species. The haloacetylphosphonates were found to be irreversible inhibitors of glyceraldehyde-3-phosphate dehydrogenase from a variety of sources. They react with the active-site thiol group (Cys-149) and are half-site reagents with yeast glyceraldehyde-3-phosphate dehydrogenase. Thus, when two of the identical four subunits are modified the enzyme is catalytically inactive. The effects of pH (7-10), 2H2O and NAD+ on the reaction with the yeast enzyme were examined in detail. NAD+ enhances the alkylation rates. The second-order rate constant does not show a simple sigmoidal dependence on pH but rather a tailing bell-shaped curve (pKa 7.0 and 8.4) qualitatively similar to that obtained with dinitrothiophenol. There is no significant solvent isotope effect on the limiting rate constants and a normal isotope effect on the two pKa values. The results are consistent with the more reactive enzyme species containing a thiolate and an acidic group that may either donate a proton to the dianionic haloacetylphosphonate or orient the inhibitor.

scholarly journals Specificity of activated human protein C

1985 ◽  
Vol 230 (2) ◽  
pp. 497-502 ◽  
Author(s):  
S R Stone ◽  
J Hofsteenge
Keyword(s):  
Amino Acid ◽  
Rate Constant ◽  
Amino Acid Residue ◽  
Protein C ◽  
Activated Protein C ◽  
Order Rate Constant ◽  
Human Protein ◽  
Functional Protein ◽  
Hydrophobic Residues ◽  
Apolar Residue

Peptide p-nitroanilide substrates and peptidylchloromethane inhibitors were used to examine the specificity of activated human Protein C. Substrates with arginine in the P1 position had the highest activity. The best substrates and inhibitors, as judged by the second-order rate constant for their interaction with the enzyme, had an apolar residue in the P2 position. In contrast with thrombin [Kettner & Shaw (1981) Methods Enzymol. 80, 826-842], activated Protein C was able to accommodate large hydrophobic residues such as phenylalanine and leucine in the P2 position. In the P3 position, the enzyme preferred an apolar D-amino acid residue. The results of the present study have also indicated a suitable substrate and inhibitor to be used in the assay of functional protein C and of thrombomodulin.

Unions and the Popular Front: The West Coast Waterfront in the 1930s

1986 ◽  
Vol 30 ◽  
pp. 59-78 ◽  
Author(s):  
Bruce Nelson
Keyword(s):  
New York ◽  
Communist Party ◽  
Good Deal ◽  
The United States ◽  
Popular Front ◽  
Human Face ◽  
History Of ◽  
Patterns Of Behavior ◽  
The Relationship ◽  
Made In

Recent discussions of the history of American communism have generated a good deal of controversy. A youthful generation of “new social historians” has combined with veterans of the Communist party to produce a portrait of the Communist experience in the United States which posits a tension between the Byzantine pursuit of the “correct line” at the top and the impulses and needs of members at the base trying to cope with a complex reality. In the words of one of its most skillful practitioners, “the new Communist history begins with the assumption that … everyone brought to the movement expectations, traditions, patterns of behavior and thought that had little to do with the decisions made in the Kremlin or on the 9th floor of the Communist Party headquarters in New York.” The “new” historians have focused mainly on the lives of individuals, the relationship between communism and ethnic and racial subcultures, and the effort to build the party's influence within particular unions and working-class constituencies. Overall, the portrait has been critical but sympathetic and has served to highlight the party's “human face” and the integrity of its members.

scholarly journals Sodium Movements in the Human Red Blood Cell

1970 ◽  
Vol 56 (3) ◽  
pp. 322-341 ◽  
Author(s):  
John R. Sachs
Keyword(s):  
Blood Cell ◽  
Rate Constant ◽  
Transport Mechanism ◽  
Extracellular Potassium ◽  
Sodium Influx ◽  
Influx Rate ◽  
High K ◽  
Inner Surface ◽  
Pump Mechanism ◽  
Made In

Measurements were made of the sodium outflux rate constant, okNa, and sodium influx rate constant, ikNa, at varying concentrations of extracellular (Nao) and intracellular (Nac) sodium. okNa increases with increasing [Nao] in the presence of extracellular potassium (Ko) and in solutions containing ouabain. In K-free solutions which do not contain ouabain, okNa falls as [Nao] rises from 0 to 6 mM; above 6 mM, okNa increases with increasing [Nao]. Part of the Na outflux which occurs in solutions free of Na and K disappears when the cells are starved or when the measurements are made in solutions containing ouabain. As [Nao] increases from 0 to 6 mM, ikNa decreases, suggesting that sites involved in the sodium influx are becoming saturated. As [Nac] increases, okNa at first increases and then decreases; this relation between okNa and [Nac] is found when the measurements are made in high Na, high K solutions; high Na, K-free solutions; and in (Na + K)-free solutions. The relation may be the consequence of the requirement that more than one Na ion must react with the transport mechanism at the inner surface of the membrane before transport occurs. Further evidence has been obtained that the ouabain-inhibited Na outflux and Na influx in K-free solutions represent an exchange of Nac for Nao via the Na-K pump mechanism.

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