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Reactions homolytic

There are very few homolytic reactions on triazolopyridines. A suggestion that the ring opening reactions of compound 1 involved free radical intermediates is not substantiated (98T9785). The involvement of radical intermediates in additions to ylides is discussed in Section IV.I. The reaction of radicals with compound 5 and its 1-substituted derivatives gives 4-substituted compounds such as 234 (96ZOK1085). A more detailed study of the reaction of the 1-methyl and 1-phenyl derivatives with r-butanol and ammonium persulfate produced 4-methyl substitution with a silver nitrate catalyst, and the side chain alcohol 235 without the catalyst (96ZOK1412). [Pg.42]


Theoretical reactivity indices of heteroaromatic systems distinguish reactivity toward electrophilic, nucleophilic and homolytic reactions. [Pg.5]

There are differences in the high temperature behavior. While oxaziridines almost always isomerize to acid amides, a similar reaction of diaziridines, which should lead to amidines, has not been observed. Sensitivity towards bases, often encountered in oxaziridines, is observed only in some special substituted diaziridines. The tendency of some classes of oxaziridines to transfer the nitrogen function also lacks in the diaziridine field. On homolytic reactions of diaziridines there are only a few observations. [Pg.212]

Homofolic acid, 5,11-methenyl-tetrahydro-biological activity, 3, 327 Homofolic acid, tetrahydro-biological activity, 3, 327 Homoisoflavanones occurrence, 3, 722 thermoisomerization, 3, 722 thermolysis, 3, 728 Homolytic reactions heterocyclic compounds reviews, 1, 74 Homophthalic acid isocoumarins synthesis from, 3, 830 synthesis, 3, 830 Homophthalic anhydride isochroman-l-one synthesis from, 3, 860 20a-Homoporphyrin nomenclature, 1, 30 Homopterocarpin isolation, 4, 998 ( )- D- Homotestosterone synthesis, 1, 453 Homer-Emmons reaction chromene synthesis by, 3, 749 Hortiacine isolation, 3, 149 Hortiamine isolation, 3, 149... [Pg.645]

If homolytic reaction conditions (heat and nonpolar solvents) can be avoided and if the reaction is conducted in the presence of a weak base, lead tetraacetate is an efficient oxidant for the conversion of primary and secondary alcohols to aldehydes and ketones. The yield of product is in many cases better than that obtained by oxidation with chromium trioxide. The reaction in pyridine is moderately slow the intial red pyridine complex turns to a yellow solution as the reaction progresses, the color change thus serving as an indicator. The method is surprisingly mild and free of side reactions. Thus 17a-ethinyl-17jS-hydroxy steroids are not attacked and 5a-hydroxy-3-ket-ones are not dehydrated. [Pg.242]

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... [Pg.8]

The nucleophilic substitution reactions are still more limited in scope owing to the instability of the isoxazole ring toward nucleophilic reagents. Homolytic reactions appear to be unknown though some of the reactions being studied are possibly of this type. Besides those reactions which are characteristic of the reactivity of the isoxazole nucleus itself, we shall consider in this section some substitution reactions in the side chain organomagnesium synthesis in the isoxazole series, condensation reactions of the methyl groups of methyl-isoxazoles, and finally some miscellaneous reactions. [Pg.382]

Whereas most reactions in the isoxazole series are undoubtedly those of electrophilic substitution, mercuration of isoxazoles, as well as some cases of mercuration of aromatic compounds, could be considered as homolytic reactions. However, the ready mercuration of... [Pg.388]

The addition of acetate ion to an arenediazonium ion is also an O-coupling. As the equilibrium of this reaction lies very much to the side of the starting ions (Suschitzky, 1967), and since diazoacetates play an important role as transient intermediates in homolytic reactions of A-nitrosoacetanilides, we will discuss diazoacetates in that context (Sec. 10.10). [Pg.115]

Dediazoniations that follow a homolytic mechanism are, however, always (as far as they are known today) faster than heterolytic dediazoniations. A good example is afforded by the rates in methanol. In a careful study, Bunnett and Yijima (1977) have shown that the homolytic rate is 4-32 times greater than the heterolytic rate, the latter being essentially independent of additives and the atmosphere (N2, 02, or argon). In water the rate of heterolytic dediazoniation, measured at pH <3, is lower than that of the homolytic reactions that take place in the range pH 8-11 (Matrka et al., 1967 Schwarz and Zollinger, 1981 Besse and Zollinger, 1981). [Pg.199]

It is likely that Cohen s method is a homolytic reaction (Sec. 8.6). The catalysis can be represented by Schemes 10-7 to 10-9. The last step of this mechanism is based on competitive hydroxy-/halo-de-diazoniations investigated by Hanson et al. (1991) and discussed in Section 10.5. [Pg.226]

Galli (1988, p. 781) does not discuss this problem in his review. However, March (1992, p. 719) emphasizes the complexity of the elementary steps in homolytic reactions forming biaryls (footnote 334). [Pg.259]

From the point of view of general synthetic applicability, Table 10-6 shows clearly that there is no overall rationale in these cyclization reactions. The range of yields is enormous and, in addition, it is hardly possible to specify whether heterolytic or homolytic reaction conditions are preferred. [Pg.262]

Br, 2,600 5-C1, 2,700 5-CN, 260277,277a. A good correlation of the substituted dimethoxybenzene data with the Hammett equation was obtained with p = —4.0 this value was taken to further confirm the heterolytic nature of the rate-determining step. The incursion of an apparently homolytic reaction was detected if the aromatics were distilled from diethyl ether, anomalously high but quite reasonably... [Pg.112]

The versatility, predictability and functional-group tolerance of free radical methodology has led to the gradual emergence of homolytic reactions in the armory of synthetic chemistry. Tin hydrides have been successfully employed in radical chemistry for the last 40 years however, there are drawbacks associated with tin-based chemistry. Organotin residues are notoriously difficult to remove from desired end products, and this, coupled with the fact that many organotin compounds are neurotoxins, makes techniques using tin inappro-... [Pg.48]

In this reaction scheme, hydrogen adsorption (on an empty site ) can occur only after OH removal. Since the adsorption energy of hydrogen is gained only in the second step, this may shift the onset of the reaction to more cathodic potentials. We wUI see later that on a surface covered by Pt monolayer islands that allow an easy formation of Had (see below), a homolytic reaction according to... [Pg.473]

Having a weak O—O bond, peroxides split easily into free radicals. In addition to homolytic reactions, peroxides can participate in heterolytic reactions also, for example, they can undergo hydrolysis under the catalytic action of acids. Both homolytic and heterolytic reactions can occur simultaneously. For example, perbenzoates decompose into free radicals and simultaneously isomerize to ester [11]. The para-substituent slightly influences the rate constants of homolytic splitting of perester. The rate constant of heterolytic isomerization, by contrast, strongly depends on the nature of the para-substituent. Polar solvent accelerates the heterolytic isomerization. Isomerization reaction was proposed to proceed through the cyclic transition state [11]. [Pg.117]

PARABOLIC MODEL OF BIMOLECULAR HOMOLYTIC REACTION 4.4.1 Main Equations of IPM... [Pg.187]

In the oxidized hydrocarbon, hydroperoxides break down via three routes. First, they undergo homolytic reactions with the hydrocarbon and the products of its oxidation to form free radicals. When the oxidation of RH is chain-like, these reactions do not decrease [ROOH]. Second, the hydroperoxides interact with the radicals R , RO , and R02. In this case, ROOH is consumed by a chain mechanism. Third, hydroperoxides can heterolytically react with the products of hydrocarbon oxidation. Let us consider two of the most typical kinetic schemes of the hydroperoxide behavior in the oxidized hydrocarbon. The description of 17 different schemes of chain oxidation with different mechanisms of chain termination and intermediate product decomposition can be found in a monograph by Emanuel et al. [3]. [Pg.207]

The concurrent slow homolytic reaction gives rise to free radicals [14]. The occurrence of the homolytic reaction can be revealed by the consumption of free radical acceptors [8,15], CL [16], or NMR spectroscopy [17,18]. The introduction of phosphite into the hydroperoxide-containing cumene causes an initiation, pro-oxidative effect related to the formation of free radicals [6]. The yield of radicals from aliphatic phosphites is much lower (0.01-0.02%) than that from aromatic phosphites (up to 5%) [17]. The homolytic reaction of phosphites with hydroperoxide has a higher activation energy than the heterolytic reaction, which results in the predominance of the former reaction at elevated temperatures. [Pg.595]

These catalytic reactions are distinguished from the homolytic reactions in that no evidence exists for paramagnetic intermediates. The epoxidation is stereospecific, trans- and c/.v-alkenes yielding trans- and o.v-epoxides, respectively. Under the same conditions, complexes of Cu, Mn, and Fe give no yields or... [Pg.80]

The observation of second-order kinetics (ku) for the spectral decay of the anisole cation radical in Fig. 15 points to the disappearance of AN + - after its separation from the initially formed triad in (63). Owing to the high yields of nitroanisoles obtained, such a process can be formulated as in Scheme 11 as the bimolecular (homolytic) reaction in (64) that produces the critical Wheland intermediate in aromatic nitration according to Perrin (1977) and Ridd (1991). [Pg.247]

Cleavage by nucleophiles 79 Acid-catalyzed reactions with nucleophiles 81 Reactions of dialkylalkylthiosulfonium ions 83 Cycloelimination reactions of alkyl thiolsulfinates 88 Homolytic reactions of aryl thiolsulfinates 92 Oxidation of thiolsulfinates by peracids 94 Isomerizations of sulfoxides and thiolsulfinates 95... [Pg.65]

Molecules in heterolytic (polar) reactions form and break bonds by "coordination" and molecules in homolytic (nonpolar or free radical) reactions form and break bonds by "colligation."75 (Two more new terms ) Heterolytic reactions occur mostly in solutions, usually involving ion formation and electrophilic or nucleophilic reactions homolytic reactions occur mostly in gases and do not involve ions because less energy is required to distance the atoms into neutral radicals.76... [Pg.234]

Only a few secondary /3-deuterium KIEs have been measured for homolytic reactions and the mechanistic utility of these, invariably small, KIEs is limited. The first secondary /3-deuterium KIE for a radical reaction was published by Seltzer and Hamilton in 1966. They found a small (kH/k0)p = 1.052 (= 1.017 per D) for the thermal decomposition of the azo-bis(l-phenylethane) (reaction (40)) at 105°C in ethylbenzene and concluded that it was due to hyperconjugation... [Pg.211]

In the past this was referred to as a homolytic reaction [23], It is clear that it would be highly unlikely that dihydrogen would be split into a metal hydride and a highly energetic hydrogen radical in this sense the term homolytic splitting is misleading. [Pg.49]

The other isolated molecule index, the free valence F, is used in discussing homolytic reactions, and determines the effect of reduction of resonance integrals between an atom r under attack and its two neighbours. Denoting the two neighbours by p and q, the change in resonance integral... [Pg.80]

Chlorine and bromine react under favourable conditions (activation by other substituent, appropriate nucleophile). Iodine may also be photosubstituted by nucleophiles but is easily induced to enter into homolytic reaction pathways. One has to bear in mind that the heavier substituents (iodine, bromine and even chlorine) increase the rate of intersystem crossing which, depending on the conditions, increases or decreases the quantum yield. [Pg.252]

The taking apart or separation of a single substance or molecular entity into two or more other substances or different molecular entities. Dissociation includes het-erolytic and homolytic reactions, the release of free ions from ion pairs, the depolymerization process of a polymer consisting of smaller subunits, etc. [Pg.206]


See other pages where Reactions homolytic is mentioned: [Pg.205]    [Pg.204]    [Pg.211]    [Pg.726]    [Pg.42]    [Pg.116]    [Pg.7]    [Pg.20]    [Pg.24]    [Pg.167]    [Pg.288]    [Pg.92]    [Pg.967]    [Pg.73]    [Pg.87]    [Pg.122]    [Pg.122]    [Pg.54]    [Pg.147]   
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See also in sourсe #XX -- [ Pg.12 ]

See also in sourсe #XX -- [ Pg.8 ]

See also in sourсe #XX -- [ Pg.200 ]

See also in sourсe #XX -- [ Pg.103 ]




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Addition reactions homolytic radicals

Bond cleavage reactions homolytic

Carbon radicals homolytic addition reactions

Chemical reaction homolytic dissociation

Cleavage reactions homolytic

Free radicals substitution homolytic bimolecular reactions

Homolytic

Homolytic (Free-Radical) Reactions

Homolytic addition bimolecular reaction

Homolytic aromatic substitution reactions

Homolytic bond fission reactions

Homolytic reactions elementary radicals

Homolytic reactions fragmentation

Homolytic reactions hydrogen atoms

Homolytic reactions of oxaziridines

Homolytic reactions radical structures

Homolytic reactions, definition

Homolytic substitution reactions

Homolytic substitution reactions allylic derivatives

Hydrides radical reactions, homolytic hydrogen atom

Intramolecular reactions homolytic additions

Radical reactions, homolytic bond

Radical reactions, homolytic bond dissociation energies

Substitution homolytic bimolecular reactions

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