Partial Deuteration Experiment

In a series of experiments [229, 230], a dramatic increase in the lifetime of the triplet state in aromatic hydrocarbons was measured when they were completely deuterated. At 77 K, naphthalene in a durene solid solution has a 2.5 s lifetime (inverse of the 

namely, Ws -t = (Equation 6.23). This line width is caused by the 

N—H stretching modes in Cr (III) complexes are important in radiationless deactivation. Deuteration of these solute molecules is accompanied by a drastic decrease in the rate of electronic relaxation (and hence increase in the lifetime of the excited states) due to the lower C—D or N—D frequencies (coish) 2400 cm ), respectively. 

From this, it appears that the description of the multimode problem using separable harmonic oscillators for the high-frequency modes is a good approximation for the analysis of a deuterium experiment. 

Eg state occurs predominantly by radiationless transition. With the 

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Hydropyridinyl radicals have given excellently resolved ESR spectra which have been assigned following MO calculations and partial deuteration experiments. Experimental results from various workers are compared in Table III for a series of C-monosubstituted 1-hydropyridinyl radicals. 

P21212i Z = 4 D = 1.663 R = 0.024 for 1,863 neutron intensities at 123 K. This is a neutron-diffraction, low-temperature refinement of a partially deuterated molecule. The undeuterated molecule had previously been studied by neutron diffraction at room temperature.10 The experiment was performed in order to seek evidence of favored replacement of hydrogen by deuterium at the anomeric hydroxyl group, but no evidence therefor was observed. 

P212121 Z = 4 Dn = 1.540 R = 0.032 for 1,051 neutron intensities at 123 K. This was an experiment similar to that of the partially deuterated / -L-arabinopyranose already described. The results here were also negative. The room-temperature, neutron-diffraction structure of the un-deuterated compound had been determined previously.11... 

In the shock tube investigation of 52, a series of experiments was performed using mixtures of THF and THF-da and also partially deuterated (3,3,4,4-D4) reactant, which enabled clear conclusions with regard to the cleavage of individual bonds. In this way it was shown that ethene is formed by elimination from the THF ring at the C-2-C-3 (C-4-C-5) (path B) and C-3-C-4 positions (path C) in a ratio of =2.2 1, which indicates that the rates of these paths are practically identical except for the statistical factor of 2. 

The MS data (negative ESI mode) provide information on the molecular mass of the partially deuterated molecules due to the use of D20 in the eluent. The MS experiments, however, were carried out via flow injection analysis (FIA-MS) on peaks that were cut from a separate chromatographic run in which H20 was used instead of D20. In this way, in addition to the fragmentation, the... 

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-... 

Partially deuterated PDMS was synthesized for NMR studies, as was described previously [21]. A detailed description of the sample preparations and the NMR experiments are given in the original p rs [7-15,21]. 

Later these experiments were repeated -with the conclusion that Morris findings were dubious. Zemany and Burton used equimolar mixtures of acetaldehyde and acetaldehyde- /4, at temperatures 510 and 465 °C, and found that partially deuterated methanes were formed in appreciable amounts. The ratio CHD3/ CD4 was found to be 1.2 and 1.0 at 510 and 465 °C, respectively (compared to the value of 1.6 obtained in the photolysis at 140 °C). These results clearly indicate the free radical origin of the methane. However, the fact that the CHD3/CD4 ratio is lower than the one found in the photolysis made the authors conclude that there IS some contribution from the molecular mechanism. An upper limit for the latter was estimated to be approximately 15 and 25 % of the total reaction at temperatures 510and465 °C, respectively. Zemany and Burton estimated the values for the ratios methane-rf3/ethane-d6 and methane-t /ethane-rfe, from which a chain length of 1000 can be derived, at 465 °C, for the Rice-Herzfeld type decomposition. 

It was proved by a separate experiment that isotope mixing in a mixture of methane and methane-i proceeds very slowly even above 600 °C. Thus, it must be concluded that, in the pyrolysis, the formation of the partially deuterated methanes is a result of free radical reactions and not of the secondary exchange of the methanes. Consequently, these results support the free radical mechanism of the acetaldehyde decomposition. 

In the experiments on reaction (10), described in detail in Section 2.3.2, Tully etal. [7] investigated the reaction of OH with deuterated and partially deuterated ethanes... 

The sequential mainchain assignment of perdeuterated proteins is achieved by collecting and analyzing 3D HNCACB, 3D HN(CO)CACB, and 4D HN(CACO)NH data (1). These sequences include "H decoupling when C is transverse and work best if H2O flip-back pulses and pulsed field gradients are employed. Complete aliphatic deuteration increases both resolution and sensitivity in these experiments by eliminating partially deuterated CHnDm moieties, which have different C chemical shifts due to the "H isotope shift. 

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