Methyl radicals, absorption spectrum reaction

Mesitylfhjorenyl anion (9MsF ) is unreactive towards Mel at temperatures below —78 °C.100 Above —60 °C the absorption spectrum of 9MsF in the presence of Mel is replaced by that of the corresponding 9-mesitylfluorenyl radical (9MsF), and 9-methyl-9-mesitylfluorene is formed in low yield, hi a study of the electron-transfer photochemistry of chrysanthemol, an intramolecular S 2 reaction of a vinylcycloprop-ane radical cation has been observed.101 hi a long series of studies of the reactivity of the acids of trivalent phosphorus and their derivatives, the behaviour of P—O nucleophiles towards arylmethyl bromide systems has been examined.102 Further evidence for an X-philic substitution/SET tandem mechanism has been obtained. 

Secondary reactions then follow involving these and subsequently formed radicals. The nature of the species formed in the primary photolytic act has been inferred from the product distribution and other kinetic evidence, and also from observations of transient spectra during flash photolysis studies. For example, spectra characteristic of CIO, BrO, and 10 have been observed following the flash photolysis of methyl chloride , methyl bromide and methyl iodide in the presence of oxygen, and the absorption spectrum of the free methyl radical has been ob-served during the flash photolysis of methyl iodide and methyl bromide. 

In the decay of the radical cation of 4-methyldiphenylamine (44), for which an electronic absorption spectrum with A.max = 689 nm was observed, the main reaction route is the formation of a benzidine-type dimer, similarly to that in the case of 39+. The dimerization rate constant is 2.3 x 104 M 1 s 1. However, in the presence of a large excess of parent molecules acting as a base, the formation of cyclized dimers was also suggested. In contrast, the formation of cyclic structures was found to be characteristic of the radical cations of 3 -substituted (45) and 3,3 -disubstituted (46) derivatives of diphenylamine. On the basis of CV measurements, the formation of dihydrodiphenylphenazine derivatives may be anticipated and, consequently, 47 is assumed to be the product of dimerization of 45. In both cases the rate constants were as fast as ca 1 x 107 M 1 s-1 the 3-methyl substituent promotes visibly the reaction between the 6-position of the phenyl ring of... 

A y-ray and electron-pulse radiolytic study of aqueous methane has been effected. The absorption spectrum of the methyl free radical has been measured in the range 210—270 nm [at 210 nm, (CH8) = 8501 mol" cmr ), and by determining its rates of formation and decay the rate constants for the reactions ... 

Reaction between iV,JV-dimethylaniline and chloranil in polar solvents yields a violet material with an absorption spectrum corresponding to that of the crystal violet cation. The diamagnetic complex (D A) and semiquinone radical were identified as intermediates. The overall course of the reaction is apparently as given above. The intermediate steps must involve an intermolecular methyl migration. 

---