Hydrogen-deuterium kinetic data

When one of the ortho hydrogens is replaced by deuterium, the rate drops from 1.53 X 10 " s to 1.38 X lO s. What is the kinetic isotope effect The product from such a reaction contains 60% of the original deuterium. Give a mechanism for this reaction that is consistent with both the kinetic isotope effect and the deuterium retention data. 

The hydrogen-deuterium exchange rates of indolizine and some methyl derivatives have been measured at 50 °C in D20/dioxane. It has been shown that the exchange rates reflect the regioselectivity of protonation. Kinetic data have been discussed using HMO and PPP calculations (71T4171). Some pKa values of indolizines and azaindolizines are given in Table 9. 

Ozaki et al. (33) compared the rate of ammonia synthesis on a doubly promoted iron catalyst with that of deuteroammonia, and found that deuterium reacts markedly faster than hydrogen imder the same reaction condition. From the kinetic data, as well as the isotope effect, they reached the conclusion that the rate-determining step of the overall reaction is the chemisorption of nitrogen on a surface mainly covered with NH radicals, and that the isotope effect is due to the fact that NH is adsorbed more strongly than ND. 

Several conclusions follow from the present results (i) The per-bond nonthermal F-to-HF reactivities for Ci-Ce alkanes are roughly equivalent. Steric and/or bond strength eflFects in these substances may give rise to 10-15% reactivity diflFerences, (ii) The deuterium kinetic isotope eflFects for the per-bond nonthermal F-to-HF (DF) reactivities are quite small for cyclopentane and C2-C5 alkanes, (iii) The nonthermal corrections to the MNR H F yields for low-reactivity hydrogen donors are negligibly small, and (iv) For reactive hydrocarbons the uniform per-bond reactivity model may be combined with the simple collision fraction mixture law and hard sphere elastic cross sections obtained from gas-liquid critical data to estimate the nonthermal H F yield corrections in MNR experiments. The simple mixture law should provide a good description of the trace nonthermal yields in experiments in which the total thermal competitor concentration is held constant. 

In the UHV the successful results of the TPR experiments towards ethene hydrogenation on different cluster sizes are further investigated. Vibrational information (IRRAS) in combination with the electronic stfucture (EES) of cluster adsorbates is believed to elucidate the size dependent behavior. In this respect, first isotope experiments with deuterium look promising to elucidate the role of the hydrogen activation in the hydrogenation reaction. In addition, the application of isothermal pMBRS will help to gain kinetic data which will make the results more widely applicable [1 ]. 

Another possibility for the comparison of the acid strength of different hydroxyl groups has been proposed, using kinetic data such as the rate of hydrogen-deuterium exchange followed by time-resolved IR spectroscopy, as has been shown upon adsorption of deutero benzene in dealuminated zeolites Y [45j. 

Hydrogen abstraction from propan-2-ol and propan-2-ol- /7 by hydrogen and deuterium atoms has been studied by pulsed radiolysis FT-ESR. A secondary kinetic isotope effect was observed for H (D ) abstraction from the C—H (C—D) bonds. The results were compared with ab initio data. In similar work, the kinetic isotope effects in H and D abstraction from a variety of other alcohols in aqueous solvents have been measured. It was found that, compared with the gas phase, the reactions exhibit higher activation energies in agreement with the ability of solvation to decrease the dipole moment from the reactant alcohol to the transition state. 

The data given in Table 7 indicate that the deuterium-tritium kinetic isotope effect in hydrogen exchange with bases is in fact positive and lies within the limits of approximate theoretical estimates (Bigeleisen, 1949 Melander, 1960 Zollinger, 1958). The differences in the values... 

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