By Alkyl Radicals

The derivative obtains when the m pairs of H-atoms are replaced by alkyl radicals. The group of the structure formula (Sec. 56) is the direct product (Sec. 27) of m factors... 

Replacing the H-atoms by alkyl radicals, that is, replacing / by the generating series r(x) of the alkyl radicals (as in Sec. 58) and representing the m C-atoms of the initial compound by the factor X , we get the generating function of the special disubstituted paraffins discussed here, namely... 

Homologous series. Consider a chemical compound containing s H-atoms which can be replaced by alkyl radicals, We call... 

AA sec acrylic acid abstraction sec hydrogen atom transfer abstraction v,v addition and micleophilicity 35 by aikoxy radicals 34-5, 124-5, 392 by alkoxycarbonyloxy radicals 103,127-8 by alkyl radicals 34 5, 113, 116 by f-amyloxy radicals 124 by arenethiyl radicals 132 by aryl radicals 35, 118 by benzovloxy radicals 35, 53, 120, 126 wilh MM a" 53, 120 by /-butovy radicals 35, 53, 55, 124 solvent effects 54, 55. 123 with alkenes 122 3 with ally I acrylates 122 wilh AMS 120, 123 wilh BMA 53, 123 with isopropenvl acetate 121 with MA 120 with MAN 121 with MMA 53, 55, 120.419 with VAc 121 with vinyl ethers 123... 

For a review that lists many rate constants for abstraction of hydrogen at various positions of many molecules, see Hendry, D.G. Mill, T. Piszkiewicz, L. Howard, J.A. Eigenmann, H.K. J. Phys. Chem. Ref. Data, 1974, 3, 937 Roberts, B.P. Steel, A.J. Tetrahedron Lett., 1993, 34, 5167. See Tanko, J.M. Blackett, J.F. J. Chem. Soc., Perkin Trans. 2,1996, 1775 for the absolute rate constants for abstraction of chlorine by alkyl radicals. 

Alkylation of the 1,2,4-triazole ring by alkyl radical species has been achieved reaction of 1-methyl-1,2,-4-triazole 37 with alkyl carboxylic acids in the presence of a silver catalyst gave the corresponding 2-alkylated triazoles 38a-e in moderate yields (Equation 9 and Table 1) <2001TL7353>. 

Enthalpies, Activation Energies, and Rate Constants of the Reduction of Hydroperoxides by Alkyl Radicals Calculated by I PM Model [68]... 

Comparison of the Thermodynamic and the Kinetic Characteristics of Substitution and Reduction of Peroxides by Alkyl Radicals... 

The intriguing point is that the actual alkylation step may be the same at the anode and cathode, presumably by alkyl radicals which, in analogy to the Paneth reaction, alkylate the metal. The lifetime of the radical ion, reactivity of the radical ion or the radical towards the metal, stabilization of the radical by adsorption on the electrode surface, stabilization of each of the intermediates by solvation, their build-up in the double layer, the potential applied, all have an important contribution to the outcome. In certain cases the ET takes place catalytically, by a mediator or under the influence of surface effects17. It is therefore important to keep in mind the possible subtle differences between cases described below that otherwise appear similar. 

Termination is principally via radical coupling forming hexabutylditin, or to a lesser degree via the coupling of ketyl radicals. In the case of the mr ketones a different mechanism is proposed. The rate of abstraction of H from the tributyltinhydride by benzylic radicals is slower than the corresponding abstraction by alkyl radicals. Since the rate at which the tributyltin radical will add to aromatic carbonyls is similar to the addition rate to aliphatic carbonyls, the dominant radical species for the tttt systems is the ketyl radical. The primary termination process involves the coupling of the predominant radical species resulting in pinacol formation. 

The abstraction ability from cyclohexane of radicals derived from dialkyl peroxides has been reported. The experiments were performed with and without the trapping agent MSD (a-methylstyrene dimer), the abstracting species being alkoxy radicals derived from the peroxides. However, some dehydro dimer yields indicated that abstraction was also occurring by alkyl radicals. 

Numerous derivatives of (1) have been thus prepared, notably 2,3-dimethyl (or dialkyl)benzofurans Bz-substituted by alkyl radicals,36,213-218 methoxyl groups,101,219-221 halogen atoms,217,222-224 aryl groups,225 acetyl groups,215,218,226 formyl groups,222,226 and carboxyl groups.226,227 The method is especially valuable in the case of formyl derivatives, which are difficult to obtain otherwise. 

The same photolytic treatment of O-acyl esters (2) in the presence of disulfides, diselenides, and ditellurides effectively produces the corresponding alkyl sulfides, alkyl selenides, and alkyl tellurides respectively, through SHi reaction on the chalcogen atoms by alkyl radicals, as shown in eq. 8.9. The reactivities somewhat depend on the kind of chalcogenides. Thus, the effective formation of alkyl sulfides requires 30 eq. of disulfides, that of alkyl selenides requires 10 eq. of diselenides, and that of alkyl tellurides requires 2 eq. of ditellurides [27, 28]. 

Since these reactions are influenced by changes in the redox potential of the metal complex, it is possible to change from one process to the microscopic reverse process by changing the ligands attached to the metal. For example, with acetate ligands cobalt(II) is stable with respect to cobalt(III), and, in the presence of bromide ions, cobalt(III) is reduced by alkyl radicals in a ligand transfer oxidation ... 

Fig. 3. Arrhenius parameters of hydrogen abstraction reactions. The curve drawn suggests the trend of the compensation phenomenon. Key o abstraction by alkyl radicals from C—H bonds (Kondratiev, 1970) A abstraction by F or Cl atoms and HO radicals from C—H bonds (Kondratiev, 1970) O abstraction by CCls radical from methane (Hautecloque, 1970) further data are given in Table 7, as follows No. 1 Nos. 2-9 No. 10 BNo. 11 0 Nos. 12,13 x No. 14 No. 15 No. 16 V Nos. 17,20,21 + Nos. 18, 19, 22, 23.

Note Pyrazine may be C-alkylated directly, e.g., by alkyl radicals also by addition to give an alkylated hydropyrazine, sometimes amenable to subsequent... 

When pyrrole 987 was subjected to the usual reaction conditions, l-(2,3-dihydro-17/-pyrrolizin-5-yl)-l-ethanone 988 was obtained as the major product. The desired diketone 989 was isolated in very low yield together with a small amount of the unexpected sulfone 984 (Equation 234). This compound is formed by alkyl radical addition at C-5, and subsequent aromatization by the loss of an acetyl radical. When pyrrole 987 was reacted with BusSnH/AIBN in the absence of CO, dihydropyrrolizines 988 and 984 were isolated in 74% and 23% yields, respectively <2000TL3035>. 

In fact, the stripping of a hydrogen by alkyl radicals is not random it depends on the degree of substitution of the carbon atom. The bond is split more easily on... 

There appears to be some specificity of attack on the different mirrors. Rice and Glasebrook find that although Zn, Cd, Bi, T1 and Pb mirrors are attacked by alkyl radicals, they are not affected by methylene on the other hand, methylene does remove Te, Sb, Se and As mirrors. Once again, there is some lack of agreement between different groups of workers. For example, Norrish and Porter find that Bi is removed by methylene, while both methylene and alkyl radicals attack Pb and Zn but slowly. Atomic hydrogen removes mirrors of As, Sb, Te, Ge or Sn, but not mirrors of Pb or Bi. Biuton et have utilised the... 

Minisci, F., Gain, R., Cecere, M., Malatesta, V., Caronna, T. Nucleophilic character of alkyl radicals new syntheses by alkyl radicals generated in redox processes. Tetrahedron Lett. 1968, 5609-5612. 

Hydrogen atoms in combination with carbon may also be replaced by alkyl radicals, by means of the halogen alkyls. Since under these conditions another radical is introduced into the molecule, it presents a method of preparing the higher members of a series from the lower, simpler ones. Various examples of this will be taken up later in labor-... 

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