Hydrogen exchange, and

M. G. Reinecke, Tetrahedron 38, 427 (1982) R. Mumgan, Meta/Zation, Conformationa/Ana/ysis, Hydrogen Exchange and Rearrangement in Amides, Doctoral thesis. University of Plorida, Gainesville, 1987 A. Weissberger and E. C. Taylor, eds.. The Chemistry of Heteroyc/ic Compounds, in Ref. 11, pp. 448—449. 

Similar reactions are available for the other alkali metals. Metalation (metal-hydrogen exchange) and metal addition to alkenes provide further routes, e.g. 

The substrate molecules may become labeled with deuterium by rapid hydrogen exchange, and then the newly labeled molecule may become cleaved in the rate-determining step. 

The occurrence of hydrogen exchange and double-bond migration in heterogeneous catalytic hydrogenation means that the hydrogenation does not necessarily... 

Deuterium-labelled Tetralin and deuterium were used to determine incorporation of hydrogen by structural position in the Tetralin and coal products. Approximately two-thirds of the protium incorporated into the Tetralin-di2 was found in the a-alkyl position, indicating that hydrogen exchange between the coal and tetralin involves the a-Tetralinyl radical. In the case of the coal products, the terms 2H >yFy and 1HX (1-Fy) were used to calculate the deuterium and protium contents or eacn structural position. Preferential incorporation was found in the a-aliphatic position of the soluble coal products, indicating that these positions participated preferentially in hydrogen exchange and addition. The... 

Larcher, A. V., Alexander, R., Rowland, S. J. and Kagi, R. I. (1986) Acid catalysis of alkyl hydrogen exchange and configurational isomerisation reactions acyclic isoprenoid acids. Organic Geochemistry 10, 1015. 

Notwithstanding the beatiful results obtained with the DF method, this one appears to be much less successful in calculating transition states and barriers for hydrogen exchange and abstraction reactions [122], Parrinello and coworkers have voiced concerns about the accuracy ofDF theory with respect to chemical reactions in solution [121]. 

EHT calculations of, 34 173 hydrogen exchange and, 33 104-116 ionic and nonionic types, 33 122 monohydride and dihydride sites, 33 120-122... 

Smith, D.L. Dharmasiri, K. Protein-ligand binding studied by amide hydrogen exchange and mass spectrometry. NATO ASI Ser. C 1998, 510, 45-58. 

Wang Y., Gross M.L. Application of hydrogen exchange and electrospray ionization mass spectrometry in studies of protein structure and dynamics, in Applied Electrospray Mass Spectrometry (Practical Spectroscopy), ed. Pramanik BN, Ganguly AK, Gross ML 2002, pp 389-410. 

Englander S.W., Kallenbach N.R. Hydrogen exchange and structural dynamics of proteins and nucleic acids. Q. Ret). Biophys. 1984, 16, 521-655. 

No eleven-vertex arachno species is known, but BjoHig" (III- and IV-NIO) 129, 132) in the presence of diborane indulges in total boron and hydrogen exchange, and a transient arachno intermediate BuHie has been suggested 124). 

Fig. 2. Plot of normalized rate vs. the activity of silicic acid for the LAWABP1 (see Table 1) glass composition at two temperatures (26 and 40 °C). Rates are all computed at steady-state conditions. Boron and Na release rates are identical at low silica activities, then decrease, and become constant at or near saturation with respect to amorphous silica (vertical dot-dashed line). Note that the B rate decreases more than the Na rate. This behaviour can be rationalized as competition between two concurrent reactions alkali-hydrogen exchange and matrix dissolution (see text). Error bars represent 2-

The hydrogenation mechanisms discussed above indicate the reversible formation of intermediates. The degree of reversibility depends on the nature of the catalyst and the alkene, and on reaction conditions. Some nonreducible internal alkenes undergo slow hydrogen exchange and isomerization, indicating that reversible steps can occur in these cases. The reversible formation of alkylmetal intermediates provides a ready explanation for the isomerization of alkenes in the presence of certain metal complexes (see Section 4.3.2). 

For the purpose of comparing the rates of nitration of different substrates, standard conditions have been defined as T = 25 °C, H0 = -6.6 (75% H2S04 at 25 °C). The procedure for the determination of standard rates from the experimentally measured rates has been evolved <75JCS(P2)1600>. The standard rates of individual substrates towards hydrogen exchange and nitration have been compared. This shows clearly that there is no unique scale of reactivity valid for electrophilic substitution reactions (75JCS(P2)1624). 

Base-catalyzed displacement reactions, such as base-catalyzed halogenation, hydrogen exchange, and condensation reactions, belong to a separate class of reactions. The reactive species, in this case, is the phenolate ion rather than unionized phenol, and the reactive positions are limited to those ortho and para to the hydroxyl group. In a guaiacyl propane unit, no reaction occurs at positions 2 and 6, and displacement at position 5 will generally proceed more rapidly than the displacement of the side chain. 

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