Deuterated reactants

It should be indicated that the methylacetylene and propylene " are more complex reactants than the nonsubstituted counterparts and depict nonequivalent hydrogen atoms at the acetylenic and methyl group (methylacetylene) and at the vinyl and methyl group (propylene). Therefore, even the detection of the atomic hydrogen loss makes it difficult to elucidate if the hydrogen atoms are lost from the methyl group, the acetylenic/vinyl units, or from both positions. In these cases, it is very useful to conduct experiments with partially deuterated reactants J3-... 

Qualitative and quantitative analyzes of resin-bound molecules with any type of IR-spectroscopy is often limited by varying absorption coefficients and an overlapping of different vibrations.The use of deuterated reactants increases the selectivity of IR analysis, due to the fact that the region of C-D stretching vibration absorptions are in the range between 2300 and 2200 cm -. This region is free of other IR absorptions. An example of quantitative IR analysis is the benzoylation of amino methyl polystyrene resin [23], Fig-... 

Figure 16.9. Benzoylation of amino methyl resin with various degrees of deuteraled reactant (bottom). Five different concentrations of non deuterated/deuterated reactants were used. Top Aromatic C-D vibration with 0-100% deuterated reactant. Middle C-D derivative spectra with 0-100% deuterated reactant. Concentration of deuterated reactants 1,0% 2,20% 3,50% 4,80% 5,100%. (Reproduced from [23].)...

Figure 16.10. Calculated loading versus theoretical loading of resin with deuteraled reactant. (Reproduced from [23].)...

The use of deuterated reactants permits the real-time monitoring of solid-phase reactions via IR-microscopy. A few resin beads were trapped in a flow-through cell which can be charged with solvents and reagents using an HPLC pump. These beads were analyzed during the amidation of amino methyl polystyrene resin with deuterated benzoic acid, demonstrating that the reaction was complete after 12.7 min [36,37]. 

In another series of experiments, isotopically labelled reactants were used to establish mechanistic details of the various reactions. For one group of these studies, appropriate deuterated reactants were obtained by introducing either ethylene-d4 or ethane-cZc into the first stage of the machine. Reactions 7-10a show the results of these experiments. In cases where a given ion was observed with more than one isotopic composition, the relative yields are noted. 

In acyclic systems, the extent of anti versus syn elimination ean be determined by use of either stereospecifically deuterated reactants or diastereomeric reactants that give different products by syn and anti elimination. The latter approach showed that elimination from 3-phenyl-2-butyl tosylate is a stereospecific anti process. ... 

Analysis of the reaction products from the partially deuterated reactants allow one to calculate positional probabilities P(i) of various sites i... 

An example of using deuterated reactants for detailed kinetic studies of transition metal catalyzed reactions in ionic hquids vras contributed by Abu-Omar and coworkers. They studied the Rh-catalyzed epoxidation of olefins at ambient temperatures using [Dglstyrene and [Dio]-cylcohexene [71]. They also applied H-NMR experiments of [D3]-diperoxorhenium, formed in situ by reaction of [D3]-methyltrioxorhenium and urea hydrogen peroxide (UHP) to determine rate constants in single turnover experiments. 

TABLE VIII Comparison of Observed and Calculated Distributions of C3A 5 Isotopic Products from Ethylene Parent-Ion Reactions Using Deuterated Reactants... 

A perplexing feature of the observations is that the same product ratio is obtained from H2C=CD2 and cisotope effect acting on die proposed transition states would cause a change in product distribution for tte deuterated reactants. 

Noller and Thomke recommend the use of deuterated reactants or deuterated catalysts (OD group on the surface of oxide instead of OH groups), and give the following criteria for the three mechanisms. 

Funahashi and Ishihara used deuterated reactants to explore complexation and observed a reduction in rate constants of 20-30%. As kn/ko < 2 this result is in keeping with a secondary kinetic isotope effect, that is to say that while important, it is possible that proton transfer is not the slowest component of the reaction pathway. ... 

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