Deuterium isotope effect, on the

Methylene-l-pyrazoline Secondary deuterium isotope effects on the reaction rate 81CJC2556... 

If the deuterium isotope effect on the rearrangement rate ( H/ D3)r is larger than unity and is approximately equal to that on the rate of dediazoniation ( H/ D3)S, it can be concluded that the ion-molecule pair 8.13 is the more likely intermediate for the rearrangement reaction. On the other hand, an isotope effect on the rearrangement rate that is smaller than or equal to unity would indicate the involvement of the benzenespirodiazirine cation 8.17 as an intermediate. 

Any mechanism which involves isoenergetic, radiationless internal conversion from C, P, or T to a high vibrational level of the ground state would be expected to show a large deuterium isotope effect on the rate of internal conversion. In the direct photolysis of perdeuterio and perhydrostilbene, Saltiel<8a) found no isotope effect on the photostationary state or upon the quantum yields of cis-to-trans and trans-to-cis conversion. 

FIGURE 2.11. 19F NMR spectrum of l,6-difhiorohexane-l,l-d2, demonstrating the deuterium isotope effect on the fluorine chemical shift... 

Wells and coworkers53 have prepared a series of deuterated tetramethyltin compounds, which they used to study the long-range deuterium isotope effects on the proton chemical shifts of tetramethyltin. The various deuterated tetramethyltin compounds, with one to four trideuteromethyl groups on the tin atom, were prepared by a series of methyl group exchanges beginning with tri-trideuteromethyltin chloride and undeuterated tetramethyltin (Scheme 12). 

Wei and collaborators180 studied the long-range deuterium isotope effects on the proton chemical shifts of tetramethyllead and chlorotrimethylplumbane. The perdeuterated analogues of these organolead compounds were generated in situ by reaction of equimolar amounts of (CD3)3SnCl and (CH3)4Pb in methanol-d, in equation 118. 

At low hydroxide-ion concentrations, the rate of approach to equilibrium after a temperature jump decreases as the hydroxide-ion concentration increases. At higher concentrations the reaction becomes first order in hydroxide ion. The value of the kinetic solvent deuterium isotope effect on the reaction shows little variation over the range of hydroxide-ion concentrations studied as shown in Fig. 19. The ratio t-1(H20)/t 1(D20) at a particular concentration of OL (L = H or D) remains within the range 2.0 to 3.0 for OL" concentrations of 0.001 to 0.100 mol dm - 3 and provides little mechanistic information. Similar results were obtained in the original work (Perlmutter-Hayman and Shinar, 1978). 

Prakash et al. (1985) used the deuterium isotope effect on the l3C NMR spectrum of [47] to provide further evidence for the symmetrical, homoaromatic nature of this ion. They prepared the specifically deuterated trishomocyclopropenyl cation [57] by superacid treatment of the corresponding alcohol [58]. The 13C NMR spectrum of [57] displayed a triplet for the deuterated methine only 0.2 ppm to higher field than the undeuterated methine, indicating only an isotopic perturbation of resonance and not a rapidly equilibrating classical ion system (see Siehl, 1987). 

A full report has now appeared of solvent effects on the rates of hydrolysis of benzyltriphenylphosphonium bromide. The remarkable increase in rate in media of low polarity is largely attributable to a shift of the pre-equilibrium between phos-phonium and hydroxide ions in favour of the intermediate hydroxyphosphorane.129 In a similar vein, a study of medium and deuterium isotope effects on the rate of hydrolysis of tetraphenylphosphonium chloride in acetone-water mixtures has been reported.130... 

The 13 C resonances in derivatives of aniline reveal that the carbon bearing a partially deuterated NH2 group appears as a multiplet because of the deuterium isotope effect on the 13C chemical shift, when the hydrogen exchange is low. This effect is larger for... 

Armstrong D, Kutob R, Sipes I. 1985. Deuterium isotope effect on the expiration and tissue distribution of 1,2-dibromoethane [Abstract]. Toxicologist 5 174. 

White RD, Gandolfi AJ, Bowden GT, et al. 1983. Deuterium isotope effect on the metabolism and toxicity of 1,2-dibromoethane. Toxicol AppI Pharmacol 69 170-178. 

The absorption cross sections of the Sn Si transition are determined from the kinetic analyses based on the two-photon absorption measurement. In contrast, tetraphenylporphin scarcely show the S2 state fluorescence. In order to elucidate the effect of the imino hydrogens on the radiationless transitions, deuterium isotope effect on the relaxation processes from the lowest excited singlet state of metal free porphyrins has been investigated. 

Recently, it was shown that in deuterated tetraphenylporphin the fluorescence quantum yield and lifetime, and the triplet yield increase in a similar manner relative to the undeuterated one (24). Such a deuterium isotope effects on the state suggested the participation of Sq internal conversion in the energy dissipating... 

Deuterium Isotope Effect on the Si v- Sq Internal Conversion of Free Base Porphyrins... 

Deuteration has been previously shown to cause an increase in the lifetime of triplet free-base porphyrins ( 7). This has been attributed to the strong coupling of N-H tautomerism with nonradiative decay. In the case of mesoporphyrin IX the increase upon deuteration is approximately two-fold ( ) As indicated in Table III deuteration of the picket fence porphyrin results in little change in the photostationary state composition but an almost twofold increase in the quantum yield of 4,0 -> 3>1. As stated above there is no measurable deuterium isotope effect on the thermal reaction the proportionate increase in quantum yield and triplet lifetime upon deuteration of the picket fence porphyrin is thus completely consistent with the adiabatic mechanism described above. Although the evidence amassed does not completely rule out other possibilities, it seems that the photoatropisomerization is to date best described by the adiabatic pathway in which the porphyrin ground and excited state potential surfaces are modified much as illustrated in Figure 3. 

Reaction of atomic carbon with alkenes generally involves both DBA and vinyl C—H insertion. An interesting example is the reaction of C atoms with styrene in which the major products are phenylallene (21) and indene (22). The synthesis of a number of specifically deuterated styrenes and the measurement of the deuterium isotope effects on the 21/22 ratio led to the conclusion that 21 was formed by DBA followed by ring expansion and by C—H(D) insertion into and followed by rearrangement of the resultant frawi-vinylcarbene (23). The indene was formed by C—H(D) insertion into Xb followed by cyclization of the resultant cw-vinylcarbene (24) (Eq. 18). An examination of the product ratios and their label distributions when atoms are used leads to the conclusion that the ratio of C=C addition to C—H insertion is 0.72 1 in this case. 

Table 1 Deuterium isotope effect on the rate constants of oxidation of 2 -deoxyguanosine 5 -monophosphate by one-electron oxidants in neutral aqueous solutions (adapted from [14] and [61]) ...

Table 2 Deuterium isotope effect on the rate constants of the oxidation of guanine and 8-oxoguanine by 2-aminopurine neutral radicals in double-stranded DNA duplexes (adapted from [11] and [13]) ...

Fig. 9 Deuterium isotope effect on the kinetics of oxidation of G by 2AP(-H) radicals in the [2AP]T2GGTio duplex in oxygenated H2O/D2O buffer solutions (pH 7.0) [13]. The kinetic profiles (resolution of 0.5 us/point) of the 2AP(-H) decay (365 nm) and the G(-H) formation (320 nm) were linearized according to a semilogarithmic form of Eq. 7. The solid lines are the best linear fits to the experimental data. Reprinted with permission from the J Phys Chem, Copyright (2001) American Ghemical Society...

Hales,D. B., Ho, B. Thompson,J. A. (1987). Inter-and intramolecular deuterium isotope effects on the cytochrome P-450-catalyzed oxidative dehalogenation of 1,1,2,2-tetrachloroethane. Biochemical and Biophysical Research Communications, 149, 319—25. 

The kinetics of hydrolysis of N-salicylidene-2-aminothiazole (119 = HL) have been studied in aqueous 5% methanol in the presence and absence of Co11, Ni, Cu11 and Zn11.408 The solvent deuterium isotope effect on the rate of spontaneous and hydroxide-catalyzed hydrolysis of the Schiff-base anion (L ) is consistent with intramolecular catalysis by the phenoxide ion. Only... 

Bielski BFIJ, Saito E (1971) Deuterium isotope effect on the decay kinetics of perhydroxyl radical. J Phys Chem 75 2263-2266... 

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