Deuterium secondary

Deuterium secondary isotope effects in an olefinic cationic polycyclization have been reviewed by Borcic and coworkers237. 

Saunders also used calculations on his model reaction (54) to determine the relationship between the secondary hydrogen-deuterium (secondary hydrogen-tritium) KIEs and secondary deuterium-tritium KIEs for doubly labelled substrates and to investigate how tunnelling affects this relationship. To obtain secondary KIEs that could be checked experimentally, Saunders calculated the secondary k lk% and k lk KIEs for the hypothetical E2 reaction of a pair of doubly labelled substrates [17] and [18]. 

Kurz, L.C. and Erieden, C. (1980). Anomalous equilibrium and kinetic alpha-deuterium secondary isotope effects accompanying hydride transfer from reduced nicotinamide adenine dinucleotide. J. Am. Chem. Soc. 102, 4198-4203... 

The a-deuterium secondary KIE (k /k -)) for the rearrangements of (2,2-dideuteriocyclo-propyl)chlorocarbene to chlorocyclobutenes 390 and 391 have been... 

Secondary deuterium isotope effect studies of solvolytic substitutions and eliminations of organic sulphonates have been reviewed by Shiner196 and by Sunko and Borcic197. In the present section, more recent works are described and general remarks on deuterium secondary isotope effects are made. 

C.L. Perrin and his students have measured [3-deuterium secondary isotope effects on amine basicities and found that deuteration increases the basicities of the compounds investigated [552]. The effect is attributed to a lowering of the ZPE of a C-H bond adjacent to an amine nitrogen. The Perrin group has also applied the same techniques to carboxylic acids and phenols [553], andpyridines [554]. 

The very small secondary isotope effect arising from replacement cf p-CHs by p-CDs is instructive largely because it shows that full development of carbonium ion character is not necessarily associated with a substantial benzylic deuterium secondary isotope effect. It must be recalled in this connection that the Hammett rho for Ki value is —4.410 and that the effect of one p-methyl group on the equilibrium corresponds to a typical cr+ value, i.e., the reaction is quite sensitive to stabilization of charge and p-methyl shows enhanced participation in stabilization. The observed effect is consistent with the analogous very small effects which have been observed in aromatic substitution (105), including bromination, for which p is —12, but smaller than those which have been reported for solvolyses of benzylic (106) and benzhydryl (107) compounds. It does not appear to be possible to draw a general conclusion from these data. 

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

Indicate mechanisms that would account for the formation of each product. Show how the isotopic substitution could cause a change in product composition. Does your mechanism predict that the isotopic substitution would give rise to a primary or secondary deuterium kinetic isotope effect Calculate the magnitude of the kinetic isotope effect from the data given. 

Replacement of a primary or secondary hydroxyl function with deuterium is usually carried out by first converting the alcohol into a mesylate or tosylate ester, which can then be displaced by treatment with lithium aluminum deuteride. The... 

The Diels-Alder reaction of a diene with a substituted olefinic dienophile, e.g. 2, 4, 8, or 12, can go through two geometrically different transition states. With a diene that bears a substituent as a stereochemical marker (any substituent other than hydrogen deuterium will suffice ) at C-1 (e.g. 11a) or substituents at C-1 and C-4 (e.g. 5, 6, 7), the two different transition states lead to diastereomeric products, which differ in the relative configuration at the stereogenic centers connected by the newly formed cr-bonds. The respective transition state as well as the resulting product is termed with the prefix endo or exo. For example, when cyclopentadiene 5 is treated with acrylic acid 15, the cw fo-product 16 and the exo-product 17 can be formed. Formation of the cw fo-product 16 is kinetically favored by secondary orbital interactions (endo rule or Alder rule) Under kinetically controlled conditions it is the major product, and the thermodynamically more stable cxo-product 17 is formed in minor amounts only. 

Important additional evidence for aryl cations as intermediates comes from primary nitrogen and secondary deuterium isotope effects, investigated by Loudon et al. (1973) and by Swain et al. (1975 b, 1975 c). The kinetic isotope effect kH/ki5 measured in the dediazoniation of C6H515N = N in 1% aqueous H2S04 at 25 °C is 1.038, close to the calculated value (1.040-1.045) expected for complete C-N bond cleavage in the transition state. It should be mentioned, however, that a partial or almost complete cleavage of the C — N bond, and therefore a nitrogen isotope effect, is also to be expected for an ANDN-like mechanism, but not for an AN + DN mechanism. 

The deuterium isotope effect for each hydrogen atom ortho to the diazonio group ( H/ D = 1.22, Swain et al., 1973b) is the largest secondary aromatic hydrogen isotope effect yet observed. It is comparable to those observed for a-deuterium in reactions involving carbocation formation from secondary aliphatic esters. Ob-... 

The secondary a-deuterium isotope effects on azo coupling reactions are small, i.e., km/kiv is very close to unity. For the reaction of the 4-nitrobenzenediazonium ion with the trianion of l-D-2-naphthol-6,8-disulfonic acid catalyzed by pyridine, km/kiv = 1.06 0.04 (Hanna et al., 1974). 

Both of these reported kinetic hydrogen-deuterium isotope effects are disturbingly small, yet they are probably too large to be considered secondary isotope effects. These results lend support to the intermediate complex hypothesis, but they can be accommodated equally well by all three of the mechanisms that have been considered. These results, therefore, afford no basis for discrimination among the possible mechanisms. 

What concerns us here are three topics addressing the fates of bromonium ions in solution and details of the mechanism for the addition reaction. In what follows, we will discuss the x-ray structure of the world s only known stable bromonium ion, that of adamantylideneadamantane, (Ad-Ad, 1) and show that it is capable of an extremely rapid degenerate transfer of Br+ in solution to an acceptor olefin. Second, we will discuss the use of secondary a-deuterium kinetic isotope effects (DKie) in mechanistic studies of the addition of Br2 to various deuterated cyclohexenes 2,2. Finally, we will explore the possibility of whether a bromonium ion, generated in solution from the solvolysis of traAU -2-bromo-l-[(trifluoromethanesulfonyl)oxy]cyclohexane 4, can be captured by Br on the Br+ of the bromonium ion, thereby generating olefin and Br2. This process would be... 

The use of secondary deuterium kinetic isotope effects in mechanistic studies of olefin bromination... 

Apart from a few studies (ref. 7), the use of deuterium kinetic isotope effects (kie s) appears to have had limited use in mechanistic studies of electrophilic bromination of olefins. Secondary alpha D-kie s have been reported for two cases, trans-stilbene fi and p-substituted a-d-styrenes 2, these giving relatively small inverse kie s of... 

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