Deuterium transfer

One can note some interesting features from these trajectories. For example, the Mulliken population on the participating atoms in Figure 1 show that the departing deuterium canies a full electron. Also, the deuterium transferred to the NHj undergoes an initial substantial bond stretch with the up spin and down spin populations separating so that the system temporarily looks like a biradical before it settles into a normal closed-shell behavior. 

The results of this study are presented in Table 4.7. As can be seen from the data in Table 4.7, decarbonylation with hydrogen or deuterium transfer to the resulting radical is a relatively efficient process. The failure to observe this reaction using acetone or acetophenone as photosensitizer would suggest a singlet pathway for the direct photolysis of the aldehyde. In agreement, decarbonylation could not be quenched by naphthalene, piperylene, or 1,3-cyclohexadiene when the aldehyde was excited directly. The reaction could, however, be somewhat quenched by the addition of tri-n-butylstannane. The products in this case were... 

Frey W, Laermer F, Elsaesser T (1991) Femtosecond studies of excited-state proton and deuterium transfer in benzothiazole compounds. J Phys Chem 95 10391-10395... 

Pfeiffer M, Lenz K, Lau A et al (1997) Analysis of the vibrational spectra of heterocyclic aromatic molecules showing internal proton and deuterium transfer. J Raman Spectrosc... 

Studies aimed at the elucidation of reaction mechanisms have been performed by many groups, notably by those of Backvall [28]. In test reactions, typically enantiopure 1-phenylethanol labeled with deuterium at the 1-position (8) is used. The compound is racemized with acetophenone (9) under the influence of the catalyst and after complete racemization of the alcohol, the deuterium content of the racemic alcohol is determined. If deuterium transfer proceeds from the a-carbon atom of the donor to the carbonyl carbon atom of the acceptor the deuterium is retained, but if it is transferred to the oxygen atom of the acceptor it is lost due to subsequent exchange with alcohols in the reaction mixture (Scheme 20.4). 

Complications that arise with this simple reaction are twofold. First, because of the low mass of the hydrogen atom its movement frequently exhibits non-classical behavior, in particular quantum-mechanical tunneling, which contributes significantly to the observed kinetic isotope effect, and in fact dominates at low temperature (Section 6.3). Secondly, in reaction 10.2 protium rather than deuterium transfer may occur ... 

Dual fluorescence spectra of many species have been studied in detail (see a review by Barbara et al. [1989]) and allow the rate constants for hydrogen and deuterium transfer to be measured as a function of temperature. As a typical example, the spectrum of 2,5-bis(2-benzox-azonile)-4-methoxyphenone... 

The temperature dependence of this rate constant was measured by Al-Soufi et al. [1991], and is shown in Figure 6.17. It exhibits a low-temperature limit of rate constant kc = 8x 105 s 1 and a crossover temperature 7 C = 80K. In accordance with the discussion in Section 2.5, the crossover temperature is approximately the same for hydrogen and deuterium transfer, showing that the low-temperature limit appears when the low-frequency vibrations, whose masses are independent of tunneling mass, become quantal at Tisotope effect increases with decreasing temperature in the Arrhenius region by about two orders of magnitude and approaches a constant value kH/kD = 1.5 x 103 at T[Pg.174]

Analysis of the pH-dependence of the kinetic parameters and competitive inhibitor K values indicates that the p/fa values of the Bi and B2 groups are 7.6 and 6.0, respectively.791 These groups have not been identified, but the observed low degree of deuterium transfer ( 8%)80 82) suggests that the basic group Bi is polyprotic and, therefore, may be the -amino group of a lysine residue. 

Thus, deuterium transfer from D20 was faster than the mixed disproportionation leading to the allylic alcohol 29, which in turn had proved to be much faster than the potential radical trapping leading to the organometallic intermediate 34. This strongly suggests that deuterium incorporation in 35 cannot occur via hydrolysis of 34 [73, 74],... 

The 57% of deuterium incorporation in 40 demonstrates that deuterium transfer from D20 was slightly faster than the hydrogen transfer from 1,4-CHD, which had been shown to be much faster than the radical trapping by a second equivalent of Cp2TiCl. As before, deuterium incorporation in 40 can therefore not occur via protonation of an organometallic intermediate, such as 41 (Scheme 28). 

Proton (Deuterium) Transfer in Phenol-Water Clusters and Fluctuations of the HB Network... 

In the framework of Marcus theory (Marcus, 1968), the difference between Gibbs energy activation for hydrogen and deuterium transfer is given by the equation... 

In this work the products from the thermal dissolution of subbitu-minous Kaiparowitz coal at 427 C in tetralin are examined by spectroscopic ( C, H, NMR), molecular weight (GPC and vapor pressure osmometry (VPO)), and elemental and hydroxyl group analysis. Some of the data presented here are a refinement and extension of data presented in part in earlier work (5). The use of 1,1-dideuterotetralin (5) in con junction with NMR to monitor the time dependence of introduction of deuterium into aliphatic and aromatic structures is presented along with the structural distributions of deuterium transferred. 

As discussed earlier, transfer of deuterium to organic reactant was observed when 2,3-dimethylbutene-1 was contacted with a synthetic partially deuterated decationated Y zeolite (DHY). From Table XIV, it is seen that such HY catalysts have appreciable catalytic activity for isomerization even at extremely lowtemperatures. Transferof deuterium to olefinic reactant was associated with a decrease in the intensity of the catalyst 0—D band near 2620 cm". Similar patterns of deuterium transfer accompanied the isomerization of 1-hexene over DHY at 25°. 

Isomerization of 1-olefins such as 1-heptene by [PdCl2(PhCN)2] in benzene at 55 C gives all possible straight chain internal olefins. Deuterium transfer from l-heptene-3-d2 to unlabeled pentene occurs during isomerization. Finally, during isomerization of... 

Figure 4.5 Probability densities for the diabatic ground state and the product state resulting from a reaction surface description of the deuterium transfer in salicylaldimine.

Figure 4.6 One-dimensional cuts through the diabatic PES forthe deuterium transfer in salicylaldimine along the substrate mode shown in the right. The thick solid lines indicate the two diabatic states shown in Fig. 4.5 for details see Ref [57].

Figure 4.7 Population dynamics of the ten lowest diabatic states of a seven-dimensional model of the deuterium transfer in salicylaldi-mine after inital population of the product...

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