Absolute rate constants for hydrocarbon autoxidation. XVI. Reactions of peroxy radicals at low temperatures

1969 ◽  
Vol 47 (20) ◽  
pp. 3803-3808 ◽  
Author(s):  
K. Adamic ◽  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Rate Constants ◽  
Low Temperatures ◽  
Equilibrium Constants ◽  
Activation Parameters ◽  
Resonance Spectroscopy ◽  
Peroxy Radicals ◽  
Ambient Temperatures ◽  
Alkyl Groups ◽  
Bond Scission ◽  
Spin Resonance

The equilibrium constants for the formation of some t-alkyl tetroxides and the rate constants for irreversible decay of the tetroxides have been measured by electron spin resonance spectroscopy at low temperatures. The equilibrium constant appears to be virtually independent of the nature of the alkyl groups. It is concluded that differences in the rate of constants for chain termination by t-peroxy radicals at ambient temperatures are due chiefly to the differences in rate constants for irreversible tetroxide decomposition. The activation parameters for this reaction indicate that it occurs by one bond rather than two bond scission.

ESR-Untersuchung zur N-Inversion an freien Radikalen / N-Inversion in Free Radical Molecules Studied by ESR

1983 ◽  
Vol 38 (5) ◽  
pp. 570-578 ◽  
Author(s):  
Volker Fischer ◽  
Werner Bühler ◽  
Klaus Scheffler
Keyword(s):  
Computer Simulation ◽  
Free Radical ◽  
Rate Constants ◽  
Time Scale ◽  
Low Temperatures ◽  
Activation Parameters ◽  
Esr Spectra ◽  
Amine Group ◽  
Ambient Temperatures ◽  
Radical State

The temperature dependence of the ESR spectra of 4-[(Mono-rsp. Di-organyl-amino)-methyl]- 2.6-di-tert.-butyl-phenoxyls is studied. The observed coalescence behaviour of the hfs-parameters of the methylene protons is interpreted by N-inversion in the amine group. Thus it is shown that the μsec time scale of ESR makes it possible to study these processes near ambient temperatures. Evaluation of rate constants and activation parameters was done by computer simulation of the DESR spectra. Comparing these values with those given by DNMR methods at low temperatures show that the radical state of the molecule has no significant effect on the inversion rate constants.

The decomposition of aliphatic N-nitro amines in aqueous sulfuric acid. Bisulfate as a nucleophile

1996 ◽  
Vol 74 (10) ◽  
pp. 1774-1778 ◽  
Author(s):  
Robin A. Cox
Keyword(s):  
Sulfuric Acid ◽  
Water Molecule ◽  
Rate Constants ◽  
Activation Parameters ◽  
Standard State ◽  
Aqueous Sulfuric Acid ◽  
Alkyl Groups ◽  
Different Temperatures ◽  
State Rate ◽  
Acid Catalyzed

In aqueous sulfuric acid, aliphatic N-nitro amines decompose to N2O and alcohols. An excess acidity analysis of the observed rate constants for the reaction shows that free carbocations are not formed. The reaction is an acid-catalyzed SN2 displacement from the protonated aci-nitro tautomer, the nucleophile being a water molecule at acidities below 82–85% H2SO4, and a bisulfate ion at higher acidities. Bisulfate is the poorer nucleophile by a factor of about 1000. Twelve compounds were studied, of which results obtained for nine at several different temperatures enabled calculation of activation parameters for both nucleophiles. The reaction appears to be mainly enthalpy controlled. The intercept standard-state rate constants are well correlated by the σ* values for the alkyl groups; the slopes are negative, with a more negative value for the slower bisulfate reaction. Interestingly the m≠m* slopes also correlate with σ*, although the scatter is bad. Key words: N-nitro amines, excess acidity, bisulfate, nucleophiles, acid-catalyzed, kinetics.

Determination of the Rates of Ring-Closure of Oxygen-Containing Analogs of Hex-5-Enyl Radical by Kinetic Electron Spin Resonance Spectroscopy

1987 ◽  
Vol 40 (1) ◽  
pp. 157 ◽  
Author(s):  
ALJ Beckwith ◽  
SA Glover
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Activation Parameters ◽  
Ring Closure ◽  
Electron Spin Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Restricted Rotation ◽  
Conformational Effects ◽  
Spin Resonance

The hex-5-enyl (1), 3-oxahex-5-enyl (6), 2-oxahex-5-enyl (9) and 2,2-dimethylbut-3- enoyloxymethyl (13) radicals have been generated by interaction of the corresponding bromides with trialkyltin or trialkylgermanium radicals, and their rate constants and activation parameters for cyclization have been determined by kinetic e.s.r . spectroscopy. The 3-oxa species (6) undergo 1,5-ring closure more rapidly than does hex-5-enyl radical (1) because of favourable stereoelectronic factors. Spectral evidence has been obtained for restricted rotation about the O-CH2* bond in the 2-oxa radical (9) as a consequence of which its ring closure is relatively slow. Similarly, 1,5-ring closure of the ester derived radical (13) is slow because of unfavourable conformational effects arising from restricted rotation about the CO-O bond. The radical (22) formed from allyl bromoacetate does not undergo ring closure. Spectral data have been obtained for various radicals (16), (19), (23), (24) formed by intermolecular addition.

scholarly journals Kinetics and Thermodynamics of the Adsorption of Lead (II) on a Activated Carbon from Coconut Shells

2013 ◽  
Vol 15 (4) ◽  
pp. 283 ◽  
Author(s):  
L. Largitte ◽  
P. Lodewyckx
Keyword(s):  
Activated Carbon ◽  
Standard Enthalpy ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Activation Parameters ◽  
Effect Of Temperature ◽  
Standard Entropy ◽  
Exponential Factor ◽  
Different Temperatures ◽  
Coconut Shells

The effect of temperature on the adsorption of lead by an activated carbon from coconut shells is investigated. The pseudo second order equation is applied to the kinetic data obtained at different temperatures in order to determine the adsorption rate constants at these temperatures. Then, the Arrhenius equation is applied to the rate constants to determine the activation energy of the sorption reaction and the pre-exponential factor. By applying the Eyring equation to the rate constants, the standard thermodynamic activation parameters of the sorption reaction can also be calculated. In addition, the isotherms of lead adsorption on the activated carbon from coconut shells, at different temperatures, are determined and fitted by the Langmuir equation. The Van’t Hoff equation is applied to the Langmuir equilibrium constants in order to determine the standard enthalpy of the sorption reaction. The other standard thermodynamic parameters<br />(Gibbs standard enthalpy and standard entropy) are deduced. The isosteric standard sorption enthalpy is also determined by using both the classical approach and an adapted Clausius Clapeyron equation. The results are identical. The value obtained is higher, but more correct than that of Langmuir. On the basis of these<br />thermokinetic parameters, the activated carbon from Coconut shells can be considered as a very efficient carbon for the sorption of lead and its sorption efficiency (rate and quantity) increase with the temperature.

Kinetics and mechanisms of the reaction of 2,4,6-trinitrocumene and 2,4,6-trinitroethylbenzene with 1,1,3,3-tetramethylguanidine in N,N-dimethylformamide solvent

1987 ◽  
Vol 65 (5) ◽  
pp. 1007-1011 ◽  
Author(s):  
Mihir K. Biswas ◽  
Arnold Jarczewski ◽  
Kenneth T. Leffek
Keyword(s):  
Carbon Atom ◽  
Complex Formation ◽  
Proton Transfer ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Activation Parameters ◽  
Reaction Parameters ◽  
Deuterium Isotope Effect ◽  
Constant Rate

The reaction of tetramethylguanidine (TMG) with trinitrocumene (TNC) and trinitroethylbenzene (TNEB) in dimethylformamide solvent has been studied with respect to products and kinetics. For TNC only σ-complex formation with the benzene ring was observed, for which the equilibrium constant, rate constants, and activation parameters were measured. For TNEB, both σ-complex formation and proton transfer from the σ-carbon atom of the ethyl group were observed. The equilibrium constants, rate constants, and activation parameters were separately determined for each reaction and a primary deuterium isotope effect, kH/kD = 13.6 (at 20 °C), was found for the proton transfer. The reaction parameters are compared to those for proton transfer from TNT to tetramethylguanidine in DMF solvent.

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