Glen A. Russell

Spin Densities in Azo-Type Radical Anions

Various methods of calculating 14N hyperfine splittings are compared with the experimental splitting constants observed for benzo[c]cinnoline, trans-azobenzene, and 1,4-dimethyltetrazine radical anions in dimethyl sulfozide [80%]—t-butyl alcohol [20%] solution. The theory of Stone and Maki gives reasonable results although better argument is obtained by use of a modified value for QCNN of 13.8 G.

Free Radical Chain Processes in Aliphatic Systems involving an Electron Transfer Reaction

Publisher Summary This chapter reviews that the occurrence of electron transfer reactions greatly expands the scope of free radical chain processes and provides a crossing of the boundary between polar and homolytic processes. The formation of a radical ion from a neutral substrate or a radical from an ion can be considered to be a type of activation. Electron transfer between radical ions and easily oxidized or reduced substrates is a common process. It explores that the mechanistic possibilities for free radical chain processes are greatly expanded by the recognition that there is a bridge between radical ion chemistry and the chemistry of separated radicals and ions because in appropriate cases radical ions can dissociate to form a radical and an ion, or conversely, radicals may add to ions to form radical ions. The occurrence of free radical chain processes involving electron transfer is likely to occur when easily oxidized or reduced substrates are involved with radical anion formation being favored by strongly basic or reductive conditions and radical cations by acidic or oxidative environments.

Reactivity of the 5-hexenyl radical toward the anion of 2-nitropropane and borohydride anion

Abstract The 5-hexenyl radical adds to the anion of 2-nitropropane with a rate constant of ≈ × 106 L/mol-s at 40°. Hydrogen atom abstraction from BH4− occurs more slowly than abstraction from CH3O− and with a rate constant less than 1 × 104 L/mol-s at 30°. The reaction of Δ5- hexenylmercury chloride with sodium borohydride in MeOH/NaOH proceeds via hydrogen abstraction by the hexenyl radical from RHgH and not from NaBH4.

Free radical substitution reactions of phenylacetylene derivatives by an addition-elimination mechanism

Phenylacetylenes (PhCCQ with Q = PhSO2, I, SPh, Bu3Sn PhCCHg) undergo free radical chain substitution reactions with RHgCl, R2Hg, (EtO)2P(O)HgCl, (PhS)2Hg or (PhSO2)2Hg. The relative reactivities of PhCCQ towards c-C6H11 · are Q = PhSO2 (65) > I (19) > Bu3Sn (1.0).

Solvent effects in the reactions of free radicals and atoms—VI : Separation of polar and resonance effects in the reactions of chlorine atoms☆

Abstract Aromatic solvents have a large effect upon the reactivity of chlorine atoms toward carbon-hydrogen bonds having different bond dissociation energies. When the difference in reactivity of two carbon-hydrogen bonds is determined by polar effects, aromatic solvents have little effect upon the relative reactivities toward chlorine atoms. Two polar effects are important in the reactions of atoms and radicals with carbon-hydrogen bonds. When extensive bond rupture in the transition state occurs, a resonance contribution to the transition state involving charge separation is important (e.g. bromine atoms). For an atom as reactive as chlorine where little bond breaking occurs in the transition state, the polar effect is best considered in terms of a repulsion curve between the chlorine atom and the carbon-hydrogen bonds, repulsion being higher the lower the electron density of the carbon-hydrogen bond.

Electron transfer processes. 34. Reactions of .alpha.-halo ketones with nucleophiles

On etudie les reactions des chlorures de p-nitro- ou p-cyano phenacyle ou de leurs derives dimethyl-1,1 avec divers nucleophiles

The reaction of carbanions with 2-substituted-2-nitropropanes : Substitution and dimerization occurring by radical chain processes involving electron transfer☆

Abstract The reaction of mono-enolate anions with O2NCMe2X where X = Cl, NO2, p-MePhSO2 yield coupling (RCOCH(R′)(CMe2NO2) and enolate dimerization products (RCOCH(R′)CH(R′)COR) by free radical chain mechanisms involving bimolecular substitution or electron transfer reactions between the enolate anion and the intermediate nitro alkane radical anion (XCMe2NO2− ).

13C‐Hyperfine Splitting in Semidiones

A number of ketyls and semidiones containing 13C have been examined by ESR spectroscopy. Grossly different values of aCOC in the ketyls (∼ 50 G) and the semidiones (∼ 1 G) allow for an easy differentiation of the two species. This is important because strained ring ketyls can undergo a decomposition reaction leading to the semidione with one additional carbonyl group added to the ketyl. Values of aCOC, aαC, and aβC for keyls and semidiones are reporduced by the Karplus–Fraenkel equation if the term QCC′C is allowed to increase by 15% when C′ is altered from methyl to t‐butyl. No evidence for the nonplanarity of di‐t‐butyl ketyl could be deduced. Some unusual long‐range 13C hfsc (aγC) have been detected in certain bicyclic semidiones possessing a nearly coplanar, zigzag arrangement of three carbon–carbon bonds with a pz orbital.

The reaction of carbanions with tert-Butyl radicals

Abstract The SRN1 free radical chain reaction of Me3CHgCl with nitronate (−O2NC(R1)(R2)) and phenone enolate (PHC(0−)C(R1)(R2)) anions yields the C-alkylation products (Me3CC(R1)(R2)N02, PhCOC(R1)(R2)CMe3). Competitive reactions between pairs of anions demonstrate that as the basicity of the anion increases the reactivity toward Me3C at first increases and then decreases. An inverted reactivity order is also observed with phenylacetonitrile anions. In early transition state reactions, the nucleophilic character of the tert -butyl radical apparently controls the reactivity by virtue of a transition state involving transfer of the electron from radical to the LUMO of the resonance stabilized anion.

Nucleophilic substitution in organomercury halides by a free-radical chain process (SRN1)

Abstract Primary and secondary alkylmercury halides react with the salts of secondary nitroalkanes to afford tertiary nitroalkanes, mercury, metal, and halide ion. The reaction is light initiated and is strongly inhibited by radical scavengers. Cyclized products resulted from the reaction of 1-chloromercury-5-hexene establishing the 5-hexene-1-yl radical as an intermediate. A chain mechanism involving radical ions is proposed to account for these substitution reactions. Aryl???nd 1-alkenylmercury halides are either unreactive towards nitronate ions or are reductively symmetrized to the bis[organo]mercury compounds and mercury metal. Alkyl mercurials are unreactive towards nucleophiles other than nitronate ions or, in the case of benzylmercury chloride, may be reduced to bibenzyl.