The Relative Activation Energies of Removal of Primary, Secondary and Tertiary Hydrogen Atoms by Methyl Radicals1

1958 ◽  
Vol 80 (2) ◽  
pp. 291-293 ◽  
Author(s):  
Francis Owen Rice ◽  
Thomas A. Vanderslice
Keyword(s):  
Activation Energies ◽  
Hydrogen Atoms ◽  
Relative Activation

scholarly journals On the catalytic dehydrogenation of naphthenes II. Competition experiments and energies of C-H bonds

1947 ◽  
Vol 190 (1022) ◽  
pp. 309-328 ◽  
Keyword(s):  
Activation Energy ◽  
Active Sites ◽  
Catalyst Surface ◽  
Resonance Energy ◽  
Activation Energies ◽  
Theoretical Treatment ◽  
Catalytic Dehydrogenation ◽  
Simple Relationship ◽  
Hydrogen Atoms ◽  
Methyl Cyclohexane

The rates of dehydrogenation in competition experiments using mixtures of two naphthenes, or a naphthene and a cyclic mono-olefine or two cyclic mono-olefines, have been examined theoretically and experimentally for the stationary state conditions. Provided the two reactants can occupy the same sites on the catalyst surface, then the ratio of the rates should be directly proportional to the ratio of the partial pressures at any instant. Theory suggests that a constant which can be derived from these competition experiments should be independent of the overall pressures, or of the initial ratio of concentrations or of the overall extent of dehydrogenation. Further, the ratio of the rates in competition should bear no simple relationship to the ratio of the individual rates alone, but should be related to the slopes of the 1/rate against 1/pressure plot for the two components considered separately. Moreover, the constant should be a ratio of two functions each of which is characteristic of one of the naphthenes. The theoretical conclusions have been confirmed experimentally which proves either that the groups of active sites on the catalyst surface are widely separated or that any set of sites is available for the reaction of any molecular species, and no interference takes place between naphthene molecules adsorbed on adjacent sites. Proof that a naphthene and cyclohexene are dehydrogenated on the same sites is supplied by the observation that a constant is obtained when different mixtures of cyclohexene and trans -1:4-dimethyl cyclohexane are allowed to compete for the surface. The ratios for methyl, ethyl, the three dimethyl and the three trimethyl cyclohexanes in competition with cyclohexane have been accurately determined at temperatures of 400 and 450° C. From the constants so derived the activation energy differences for the removal of the first pair of hydrogen atoms has been obtained. These values are discussed in terms of the possible transition complexes, and it is shown that the reaction proceeds by the loss of a pair of hydrogen atoms simultaneously and not by a half-hydrogenated state mechanism. Using these activation energies and the experimentally found overall activation energy of 36 kcal./g. mol., the resonance energy per resonating structure was determined as 1-73 kcal. This is in good agreement with the energies of C-H bonds in alkyl radicals (2-2 kcal./g.mol./ resonating structure). The theoretical treatment suggests that the weakest C-H link in methyl cyclohexane should be in the three position to the methyl group. A study of the activation energies involved shows that the methyl cyclohexene produced from methyl cyclohexane is not 1-methyl-1-cyclohexene, thus confirming the theoretical deduction.

Calculation of the relative activation energies for reactions forming metal sulfides

1977 ◽  
Vol 12 (2) ◽  
pp. 213-215 ◽  
Author(s):  
Yu. N. Makurin ◽  
V. I. Dvoinin ◽  
G. A. Kitaev
Keyword(s):  
Activation Energies ◽  
Metal Sulfides ◽  
Relative Activation

THE ABSTRACTION OF HYDROGEN ATOMS FROM AMINES AND RELATED COMPOUNDS

1960 ◽  
Vol 38 (8) ◽  
pp. 1339-1345 ◽  
Author(s):  
R. K. Brinton
Keyword(s):  
Reaction Rates ◽  
Activation Energies ◽  
Methyl Radicals ◽  
Hydrogen Atoms ◽  
Temperature Range ◽  
Exponential Factors ◽  
Related Compounds

The reaction of methyl radicals with a group of amines and amine-like compounds has been investigated in the temperature range 125° to 157 °C. The abstraction activation energies of hydrogen atoms from these compounds, the corresponding pre-exponential factors, and the actual reaction rates indicate that the N—H hydrogen atoms are more labile than the C—H atoms in these compounds.

Hydrogen–Water Deuterium Exchange over Unsupported Group VIII Noble Metals

1974 ◽  
Vol 52 (16) ◽  
pp. 2960-2967 ◽  
Author(s):  
Norman H. Sagert ◽  
Rita M. L. Pouteau
Keyword(s):  
Noble Metals ◽  
Chemical Activation ◽  
Activation Energies ◽  
Graphitized Carbon Black ◽  
Hydrogen Chemisorption ◽  
Group Viii ◽  
Hydrogen Atoms ◽  
Hydrogen Water ◽  
Surface Areas ◽  
Specific Activities

Specific activities of unsupported powders of all six Group VIII noble metals have been determined for hydrogen – water deuterium isotope exchange. The metal surface areas, which are required to calculate the specific activities were measured by hydrogen chemisorption and were checked by electron microscopy. Specific activities were measured as a function of temperature in the range 353 to 573 K and also as a function of the partial pressure of hydrogen and water at suitable temperatures and over a tenfold range of partial pressures.The variation in the specific activities was Pd < Ir ≤ Ru < Rh < Os < Pt, and these specific activities varied over a range of about 1000. The observed orders with respect to hydrogen and water are shown to be consistent with a mechanism in which chemisorbed hydrogen atoms exchange with physically adsorbed water.From the orders and the apparent activation energies, the chemical activation energies (E0) were calculated. These varied randomly within the range 61 ± 6 kJ mol−1 for all the metals studied. Previously we showed that there was a correlation of E0 with the work function of the metal when metals were supported on a highly graphitized carbon black, and suggested that electron donation from the carbon to the metal was responsible for the correlation. This suggestion is supported by the present results which show that E0 is relatively constant for all six metals in the absence of a support.

Remarks on the diffuse interstellar lines

1967 ◽  
Vol 31 ◽  
pp. 91-93 ◽  
Author(s):  
G. Herzberg
Keyword(s):  
Hydrogen Atoms ◽  
Interstellar Gas

It is suggested that the diffuse interstellar lines are produced in the interstellar gas by molecules consisting of a few hydrogen atoms and one other atom, such as CH4+ or NH4. Diffuseness of the lines is assumed to result from predissociation of these molecules.

Sign in / Sign up

Export Citation Format

Share Document