THE SECONDARY HYDROGEN ISOTOPE EFFECTS IN THE PYROLYSIS OF ETHYL-d5 ACETATE AND ETHYL ACETATE-d3

1960 ◽  
Vol 38 (9) ◽  
pp. 1407-1411 ◽  
Author(s):  
Arthur T. Blades ◽  
P. W. Gilderson
Keyword(s):  
Ethyl Acetate ◽  
Rate Constant ◽  
Hydrogen Isotope ◽  
Experimental Error ◽  
Relative Rate ◽  
Isotope Effects ◽  
Relative Rate Constant ◽  
Temperature Ranges ◽  
Relative Rate Constants ◽  
Constant Expression

Rate constant expressions have been obtained for ethyl acetate and ethyl-d5 acetate in the temperature ranges 500–603 °C and 501–614 °C.[Formula: see text]By measuring the relative rate of production of C2H4 and C2D4 from identical mixtures of the two esters at the temperatures 387 and 490 °C, it has been possible to determine the temperature coefficient of the relative rate constant more accurately. This, coupled with the relative rate constants at 500 °C derived from the above equations, gives the relative rate constant expression.[Formula: see text]These data are compared with the intramolecular isotope effect in the decomposition of ethyl-1,1,2,2-d4 acetate, and the differences attributed to secondary isotope effects.The rate of decomposition of ethyl acetate-d3 was found to be identical within experimental error with that of the normal acetate.

THE HYDROGEN ISOTOPE EFFECTS IN THE PYROLYSIS OF ETHYL-1,1,2,2-d4 BROMIDE AND OF ETHYL-d5 BROMIDE

1962 ◽  
Vol 40 (8) ◽  
pp. 1533-1539 ◽  
Author(s):  
Arthur T. Blades ◽  
P. W. Gilderson ◽  
M. G. H. Wallbridge
Keyword(s):  
Isotope Effect ◽  
Rate Constant ◽  
Hydrogen Isotope ◽  
Relative Rate ◽  
Isotope Effects ◽  
Side Reaction ◽  
Relative Rate Constant ◽  
Temperature Range ◽  
Rate Controlling Step ◽  
Constant Expression

The relative rate constant expression has been obtained for the decomposition of ethyl-1,1,2,2-d4 bromide under inhibiting conditions in the temperature range 697.6 to 999.1 °K,[Formula: see text]The pressure dependence of the isotope effect has been investigated both with and without inhibitor, and in each case it has been shown that the isotope effect increases with decreasing pressure.The relative rate constant expression for the ethyl-h5, ethyl-d5 bromide comparison was also obtained in the temperature range 730.9 to 964.8 °K,[Formula: see text]The isotope effect is again pressure dependent, falling to lower values as the pressure is decreased.The data are used to demonstrate that the inhibited decomposition of ethyl bromide is primarily a molecular process, and that the rate-controlling step involves a carbon–hydrogen bond break.A side reaction that produces small amounts of ethane has been observed.

THE HYDROGEN ISOTOPE EFFECT IN THE PYROLYSIS OF ETHYL-1,1,2,2-d4 CHLORIDE

1962 ◽  
Vol 40 (8) ◽  
pp. 1526-1532 ◽  
Author(s):  
Arthur T. Blades ◽  
P. W. Gilderson ◽  
M. G. H. Wallbridge
Keyword(s):  
Isotope Effect ◽  
Hydrogen Isotope ◽  
Pressure Effect ◽  
Relative Rate ◽  
Isotope Effects ◽  
Deuterium Atom ◽  
Qualitative Explanation ◽  
Relative Rate Constant ◽  
Hydrogen Isotope Effect ◽  
Constant Expression

The hydrogen isotope effect in the pyrolysis of ethyl-1,1,2,2-d4 chloride has been investigated in the temperature range 758–989 °C, yielding the relative rate constant expression[Formula: see text]where kH and kD are the rate constants for the production of C2D4 (and HCl) and of C2D3H (and DCl) per β-deuterium atom respectively.The isotope effect is pressure dependent, its value increasing with decreasing pressure. The pressure effect in ethyl chloride has also been studied, and a qualitative explanation is given for the pressure dependence of intermolecular and intramolecular isotope effects.The data are compared with the isotope effects in ethyl-d4 bromide and ethyl-d4 acetate, and the conclusion is reached that the evidence supports a four-centered transition-state complex in the case of the halides.

Kinetics of the thermal decomposition of cyclobutanone

1969 ◽  
Vol 47 (4) ◽  
pp. 615-617 ◽  
Author(s):  
Arthur T. Blades
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Carbon Monoxide ◽  
Rate Constant ◽  
Relative Rate ◽  
Relative Rate Constant ◽  
Pressure Sensitive ◽  
Photochemical Decomposition ◽  
Kinetics Of ◽  
Constant Expression

The thermal decomposition of cyclobutanone into cyclopropane and carbon monoxide has been shown to occur simultaneously with the major decomposition to ethylene and ketene. The relative rate constant expression is given by [Formula: see text] Both reactions are pressure sensitive below 10 Torr and this quasi-unimolecular behavior is most pronounced in the cyclopropane forming reaction, consistent with the higher activation energy. The data are also discussed in relation to the photochemical decomposition and it is shown that cyclopropane formation from the ground singlet is an important feature of the photolysis at 3130 Å.

Solvent isotope effects as a probe of general catalysis and solvation in phosphoryl transfer

1996 ◽  
Vol 74 (6) ◽  
pp. 931-938 ◽  
Author(s):  
Clinton D. Bryan ◽  
K. Barbara Schowen ◽  
Richard L. Schowen
Keyword(s):  
Ionic Strength ◽  
Transition State ◽  
Rate Constant ◽  
Relative Rate ◽  
Isotope Effects ◽  
Phosphoryl Transfer ◽  
Relative Rate Constant ◽  
Nitrophenyl Phosphate ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

Phosphoryl transfer to methanol from tris(p-nitrophenyl) phosphate (PNNN), methyl bis(p-nitrophenyl) phosphate (PMNN), and dimethyl p-nitrophenyl phosphate (PMMN) exhibits general base catalysis by acetate ion but no detectable catalysis by acetic acid. For PNNN, acetate catalysis produces normal solvent isotope effects kROH/kROD of 1.68 ± 0.01 at high ionic strength (0.475) and 1.77 ± 0.04 at low ionic strength (0.048). A linear proton inventory indicates most simply that the isotope effect arises from a one-proton catalytic bridge in the transition state, although this model cannot strongly be distinguished from a generalized solvation effect. Reactions of methoxide ions produce slight inverse isotope effects kROD/kROH of 1.1–1.2, far smaller than the inverseeffect of about 2.5 expected for complete and uncompensated desolvation of the reactant-state methoxide ion. The transition state is thus stabilized by substantial interaction with the solvent. The proton inventory for the least reactive substrate PMMN (relative rate constant 1) is suggestive of transition-state stabilization by a combination of one-proton catalytic bridge(s) and distributed sites, while the proton inventory for the most reactive substrate PNNN (relative rate constant 1388) suggests only generalized transition-state solvation (many distributed sites); the proton inventory for PMNN, a substrate of intermediate reactivity (relative rate constant 60), suggests an intermediate situation. The data are consistent with a model in which transition states with exterior concentrations of charge favor stabilization of the charge by isotope-fractionating one-proton bridges, while transition states with distributed charge favor stabilization of the charge by many distributed sites. Key words: phosphoryl transfer, proton inventories, solvent isotope effects.

Hydrogen Isotope Exchange in 2-Butanone. Further Measurements and Some Comments

1972 ◽  
Vol 50 (19) ◽  
pp. 3239-3241 ◽  
Author(s):  
R. A. Cox ◽  
J. W. Thorpe ◽  
J. Warkentin
Keyword(s):  
Acetic Acid ◽  
Temperature Dependence ◽  
Rate Constants ◽  
Hydrogen Isotope ◽  
Isotope Exchange ◽  
Relative Rate ◽  
Aqueous Media ◽  
Acetate Buffer ◽  
Isokinetic Temperature ◽  
Relative Rate Constants

The ratio of rate constants for exchange at the methylene and methyl positions of butanone, [Formula: see text], is shown to be near 1.69 in 1:1 acetic acid–acetate buffer; nearly twice the value (0.86) for deuterioxide catalysis at 54.8°. Methods of obtaining rate constants for acetate catalysis from composite rates (acetate and deuterioxide), or from rates in buffered media, are shown to be adequate for estimating rate ratios.Detailed temperature dependence of the relative rate constants for either system is not yet available but the effects are known to be small. For butanone enolizations the isokinetic temperature is in the neighborhood of 35°, when reaction is catalyzed by deuterioxide in aqueous media.

Arrhenius-Parameter und kinetischer Isotopeneffekt für die Reaktion von Wasserstoffatomen mit Silan

1974 ◽  
Vol 29 (3) ◽  
pp. 493-496 ◽  
Author(s):  
Peter Potzinger ◽  
Louis C. Glasgow ◽  
Bruno Reimann
Keyword(s):  
Kinetic Isotope Effect ◽  
Relative Rate ◽  
Isotope Effects ◽  
Preexponential Factor ◽  
Kinetic Isotope Effects ◽  
Hydrogen Atoms ◽  
Kinetic Isotope ◽  
Abstraction Reaction ◽  
Upper Limits ◽  
Relative Rate Constants

The Reaction of Hydrogen Atoms with Silane; Arrhenius Parameters and Kinetic Isotope Effect Relative rate constants were measured for the systems H + C2H4/SiD4 and D + C2D4/SiH4 over a wide temperature range. From the known arrheniusparameter for the reaction H + C2H4 the activation energy EA and the preexponential factor A of the abstraction reactionH + SiD4 → HD + SiD3may be calculated. Values of EA = 3.2 kcal/Mol and A = 4.92 • 1013 cm3 Mol-1 sec-1 were obtained. Upper limits for the kinetic isotope effects are given in the paper

Secondary deuterium kinetic isotope effects on the thermolysis of 1-pyrazolines

1968 ◽  
Vol 46 (21) ◽  
pp. 3301-3304 ◽  
Author(s):  
Basil H. Al-Sader ◽  
Robert J. Crawford
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Relative Rate ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Relative Rate Constants

Secondary kinetic isotope effects on four deuterated 1-pyrazolines support the formation of a trimethylene intermediate during gas phase thermolysis. Calculation of cyclization relative rate constants for the trimethylene intermediates reveals that substitution of hydrogen by deuterium has no effect when the terminal methylenes are substituted, but the rate constants are decreased when the central methylene's hydrogens are substituted. Explanations are advanced for all of the observed effects.

scholarly journals Notable Substituent Effects on the Rate Constant of Thermal Denitrogenation of Cyclic Azoalkanes: Strong Evidence for a Stepwise Denitrogenation Mechanism

2010 ◽  
Vol 63 (12) ◽  
pp. 1615 ◽  
Author(s):  
Chizuko Ishihara ◽  
Manabu Abe
Keyword(s):  
Rate Constant ◽  
Linear Correlation ◽  
Strong Evidence ◽  
Bond Cleavage ◽  
Relative Rate ◽  
Substituent Effects ◽  
Relative Rate Constant ◽  
Rate Determining Step ◽  
Singlet Diradicals ◽  
Type Radical

The thermal denitrogenation rates (k) of a series of 7,7-dimethoxy-1,4-diaryl-2,3-diazabicyclo[2.2.1]hept-2-ene derivatives 2 with a variety of aryl groups (p-CNC6H4, C6H5, p-MeC6H4, p-MeOC6H4) were determined to investigate the denitrogenation mechanism. A linear correlation (r = 0.988) between the relative rate-constant (log krel) of the denitrogenation reaction and Arnold’s σα• parameter for benzylic-type radical-stabilization was observed. However, the relative rate-constant was not correlated with the substituent effect on the lifetime of the resulting singlet diradicals DR2. These results indicate that the rate-determining step of denitrogenation of 7,7-dimethoxy-2,3-diazabicyclo[2.2.1]hept-2-ene derivatives involves stepwise C–N bond cleavage.

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