Cleavage reactions heterolytic

A more detailed mechanistic analysis reveals that in the case of an Sn2 reaction both R—C and HO are involved in the rate-deterrniriitig step (formation of the transition state), while in a SnI reaction heterolytic cleavage of the C—X bond is the rate-determining step, and, thus, only the concentration of R—X influences the kinetics. Scheme 2.2.7 displays the two different borderline cases and their ratedetermining steps. 

Heterogeneous reaction (Section 6 1) A reaction involving two or more substances present in different phases Hydro genation of alkenes is a heterogeneous reaction that takes place on the surface of an insoluble metal catalyst Heterolytic cleavage (Section 4 16) Dissociation of a two electron covalent bond in such a way that both electrons are retained by one of the initially bonded atoms Hexose (Section 25 4) A carbohydrate with six carbon atoms High density lipoprotein (HDL) (Section 26 11) A protein that carries cholesterol from the tissues to the liver where it is metabolized HDL is often called good cholesterol Histones (Section 28 9) Proteins that are associated with DNA in nucleosomes... 

It has recently been suggested that a free radical mechanism i.e., homo-lytic cleavage of the oxygen-oxygen bond rather than the heterolytic cleavage pictured) may be involved in the reaction of some substituted benzophenones and peroxyacetic acid. 

The broadest classification of reactions is into the categories of heterolytic and homolytic reactions. In homolytic (free radical) reactions, bond cleavage occurs with one electron remaining with each atom, as in... 

Compound 104 could not be obtained from 103, and a hypothesis about its formation considered the (homolytic or heterolytic) cleavage of the O—N bond (Scheme 43) (68TL2417). The sensitized reaction didnotgive adifferentresult the author supposed that the reaction involved the excited triplet state of the molecule. When the reaction was carried out in methanol, 104 was obtained in 8% yield... 

Potassium peroxodisulphate (K2S2Og) also oxidizes sulphoxides to sulphones in high yield, either by catalysis with silver(I) or copper(II) salts at room temperature85 or in pH 8 buffer at 60-80 °c86-88. The latter conditions have been the subject of a kinetic study, and of the five mechanisms suggested, one has been shown to fit the experimental data best. Thus, the reaction involves the heterolytic cleavage of the peroxodisulphate to sulphur... 

Chemical reaction rate, see Rate of reaction Chemical reactions condensed phases, 42-46 enzymatic, see Enzymatic reactions gas phase, see Gas-phase reactions heterolytic bond cleavage, 46, 47, 51,... 

In contrast to the abundant examples of radical cleavage, only a few proposals of ionic cleavage of carbon-carbon a bonds have been put forward in the long saga of mechanistic studies on heterolytic cleavage reactions. 

The enantioselective P-borylation of a,P-unsaturated esters with (Bpin) was studied in the presence of various [CuCl(NHC)] or [Cu(MeCN)(NHC)] (NHC = chiral imidazol-2-ylidene or imidazolidin-2-ylidene) complexes. The reaction proceeds by heterolytic cleavage of the B-B bond of the (Bpin), followed by formation of Cu-boryl complexes which insert across the C=C bond of the unsaturated ester. Best yields and ee were observed with complex 144, featuring a non-C2 symmetric NHC ligand (Scheme 2.31) [114]. 

The reaction of OsHCl(CO)(P Pr3)2 with HC1 gives the dichloro derivative OsCl2( n2-H2)(CO)(PIPr3)2.35 In solution, this complex is stable under argon for a matter of days. However, the dihydrogen unit is highly activated toward heterolytic cleavage, as demonstrated by deprotonation with NaH and by reactions with carbon monoxide and /ert-butyl isocyanide, which afford OsHCl(CO)L(P Pr3)2 (L = CO, r-BuNC) and HC1. 

This review has been concerned largely with interactions and reactions of unsaturated hydrocarbons with zinc oxide. The picture of the active site as a metal oxide pair capable of heterolytic fission of an acidic C—H bond provides a consistent framework for discussion of these results. We believe this view may be generally applicable. In its application, however, we must keep in mind that zinc oxide may be much more effective for heterolytic cleavage (i.e., more basic) than oxides such as, say, alumina.4... 

Figure 4. Reaction Mechanism for N-Acetoxy Arylamines (V). Ac, acetyl RSCH3 methionine RNH2, N2-guanine-nucleosides, -nucleotides, or -nucleic acids RCH, C8-guanine-nucleo-sides, -nucleotides, or -nucleic acids. Pathways and heterolytic cleavages a and b are discussed in the text. Dashed arrows indicate proposed pathways.

Photosolvolysis of some vinyl iodonium substrates can be compared with thermal solvolysis of the same substrates. Photochemical reaction of (E)- and (Z)-2-phenylprop-l-enyl(phenyl)iodonium tetrafluoroborate (31) in methanol and TFE gave products of heterolytic cleavage of vinylic C-I bond as summarized in Table III (for the product structures see eq 14.17 In contrast to... 

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