Methyl radicals, absorption spectrum

After the first unsuccessful attempts to record a matrix IR spectrum of the methyl radical, reliable data were obtained by the use of the vacuum pyrolysis method. IR spectra of the radicals CH3 and CD3 frozen in neon matrices were measured among the products of dissociation of CH3I, (CH3)2Hg and CD3I (Snelson, 1970a). The spectra contained three absorptions at 3162 (1 3), 1396 V2) and 617 cm (I l) belonging to the radical CH3 and three bands 2381, 1026 and 463 cm assigned to the radical CD3. Normal coordinate analysis of these intermediates was performed and a valence force field calculated. In accordance with the calculations, methyl radical is a planar species having symmetry >31,. 

Ito and Matsuda studied the y-radiolysis of 2-methyltetrahydrofuran (MTHF) solutions of diphenyl sulfone and dibenzothiophene-S,S-dioxide (DBTSD) at 77 K. They found that the radical anions of these sulfone compounds are formed and have intense absorption bands at 1030 nm and 850 nm, respectively. The blue glassy solution of y-irradiated diphenyl sulfone has absorption bands at both 1030 nm and 360 nm while the absorption spectrum of the benzenesulfonyl radical formed by UV irradiation of diphenyl sulfone solution at 77 K showed only a peak at 382 nm. Gamma-irradiated phenyl methyl sulfone solution showed an absorption band only at 385 nm. Consequently the appearance of the absorption bands in 800-1030 nm of diphenyl sulfone and DBTSD may suggest that the unpaired electron is delocalized on two phenyl rings. The same authors studied the radiolysis of MTHF solutions of disulfones (diphenyl and dihexyl disulfones). They found a blue coloring of the solution by the y-radiolysis of diphenyl disulfone and dihexyl disulfone due to absorption peaks at 695 nm and 690 nm respectively, besides smaller absorptions at 300-400 nm. Comparing these results to the previous observation, that phenyl methyl sulfone solution absorbs only at 398 nm, results in the conclusion that the absorption band at 690 nm is due to the linked two sulfone moieties. The authors found that substituents on the phenyl ring lead to shifts in the absorption maxima of the... 

Photolysis in the gas phase leads to the quantitative production of nitrogen and methyl radicals. Photolysis in solution, however, results in a shift in the absorption spectrum to longer wavelengths due to the production of a new species, which is identified as the cw-azomethane (the trcms configuration is the normal isomer). Similarly, irradiation of tro/u-azoisopropane<3) results in trans-cis isomerization to the cis isomer ... 

The optical spectrum of a triplet aromatic carbene can be recorded at low temperature and generally consists of two or more absorption bands. The position of these bands is often similar to the closely related transitions found in the correpsonding radical (Trozzolo and Gibbons, 1967). For example, DPM has absorptions with maxima near 300 and 465 nm and the diphenyl-methyl radical exhibits maxima at 336 and 515 nm (Porter and Strachan, 1958). 

The absorption spectrum of the methyl radical has been observed by Herzberg11 during the flash photolysis of methyl iodide and bromide, but... 

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. 

ESR spectrum for the methyl radical recorded as the first derivative of the absorption spectrum... 

Figure 2. a) Transient absorption spectra recorded after excitation of di- -butyltetramethylindo-carbocyanine benzyltriphenylborate in benzene solution with a 18 ps laser pulse. Negative absorbance related to the bleaching of the dye absorption. The band at Amax = 430 nm is attributed to the presence of the cyanine dye radical b) transient absorption spectra recorded after excitation of naphthyltriphenyl borate in benzene solution with a 18 ps laser pulse. The new feature is attributed to the presence of the (2-naphthyl)methyl radical c) the difference spectrum obtained by subtracting spectrum A from spectrum B the maximum at 385 nm is characteristic for the 2-methylnaphthyl radical. Data are taken from [25],... 

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. 

There is normally interaction with more than one magnetic nucleus. Consider, for example, the methyl radical. Each proton may be in either of two spin states, a and jS, so that there are four possible resultant magnetic spin-states ,a,a ,a,jS a,j8,j8 j8,j8,)3. The spectrum therefore has four components, and since the configurations ,a,j8 and a,j3,j8 may each be achieved in three ways whereas the other two configurations are unique, the relative intensities of the absorptions are 1 3 3 1. The resulting spectrum is shown in Fig. 1 the radical was generated by the interaction of t-butyl hydroperoxide with titanous ion (Section IID) and the hyperfine splitting constant, —the separation of the mid-points of... 

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... 

From the seeds of Castilleja rhexifolia deoxyrhexifoline (24) was isolated (35). The molecular ion was observed at m/z 191, 16 amu less than 23, and the difference of one oxygen atom was confirmed by high-resolution measurement. The base peak was observed at m/z 176 due to loss of a methyl radical. No hydroxyl absorption was seen in the IR spectrum, and the NMR spectrum showed no downfield oxymethine proton. Rather, two sets of methylene protons (3.38,3.13 ppm 2.38,1.67 ppm) were seen. Thus, the alkaloid was deduced to be the 5-deoxy derivative and was named deoxyrhexifoline (24) (35). The relationship between methyl boschniaki-nate and deoxyrhexifoline has not been established, but the available data would appear to indicate that they are the same alkaloid. Neither group reported an [a]D for the respective isolates. 

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 ... 

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