Methyl radical spectrum

The methyl radical spectrum enhanced by the photobleaching decays at 77 180 K. The disappearance of the methyl radical is partly complemented by the formation of the side chain radical, -COOCH2, due to the abstraction of a hydrogen atom from the side chain ester group, -COOCH3. 

Precise description of the pyramidal structures would also require that the bond angles be specified. The EPR spectrum of the methyl radical leads to the conclusion that its structure could be either planar or a veiy shallow pyramid. The IR spectrum of the methyl radical has been recorded at very low tempertures in frozen argon. This IR study puts a maximum of 5° on the deviation from planarity. A microwave study has also indicated... 

Information regarding the position of the substituents can be obtained from the mass spectra of the enamines of cyclic ketones. For instance in the case of the morpholine enamine of 3-methylcyclohexanone, which is shown to be a 2 1 mixture of/ and isomers by NMR spectroscopy, the fragmentation of the radical ion from the /) isomer results in the loss of a methyl radical from the C-3 position. The d isomer gives a complicated spectrum due to the loss of the hydrogen radical. 

Through radical trapping and ESR spectrum the same radical, i.e., A/-methyl-p-toluidine methyl radical, as in the BPO-DMT system was verified but with a weakened signal. Therefore, the above result favored our formerly proposed mechanism as follows ... 

In Figure 7 the peak at m/e 142, which shifts to m/e 148 in the mass spectrum of 10a and remains at m/e 142 in the spectrum of the D20-exchanged analog, probably arises by the loss of the C-3 and C-4 side chains. This ion could fragment further by eliminating a methyl radical from the ketal to give an ion at m/e 127 which shifts to m/e 130. 

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,. 

The EPR spectrum shows, in accordance with the XPS results, no feature that can be attributed to Ti centers. What is the nature of the radical observed in the EPR spectrum It might be thought that methyl radicals are the most natural products in the reduction of a mixed titaniiun-chlorine-methyl species according to the following simple reaction scheme ... 

However, a comparison of the line shape of the observed spectra with spectra of methyl radicals (Fig. lib) clearly proves that the species present here are not methyl radicals. The EPR spectrum of a methyl radical is a quartet of lines. However, the observed spectrum, though dominated by a quartet structure, shows a couple of additional lines pointing to additional interactions of the unpaired electron. By comparing the observed line shape to other alkyl radicals it turned out that the present spectrum can be attributed to ethyl radicals. Figure 11c shows the EPR spectrum of ethyl radicals created in an ethylchloride matrix generated by photolysis for comparison [121]. 

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 electron impact mass spectrum of methyl isobutyrate, 27, contains a signal for a [M—CH3]+ ion. 2H- and 13C-labelling clearly establishes that the eliminated methyl radical originates exclusively from the intact PCH3 group (6)12,13,1 . 

One other aspect of the photolysis of coordinate spin labeled derivatives is of interest. Nitroxides are good free radical scavengers (123). As a result, when methyl-cobalamin is photolyzed in the presence of a nitroxide, the methyl radical generated will react with the free nitroxide and cause disappearance of the ESR spectrum (123). However, once the nitroxide is coordinated it is no longer susceptible to attack by free radicals. Thus the nitroxyl function is quite well protected from approach by other species. 

Equation (2.3) describes line positions correctly for spectra with small hyperfine coupling to two or more nuclei provided that the nuclei are not magnetically equivalent. When two or more nuclei are completely equivalent, i.e., both instantaneously equivalent and equivalent over a time average, then the nuclear spins should be described in terms of the total nuclear spin quantum numbers I and mT rather than the individual /, and mn. In this coupled representation , the degeneracies of some multiplet lines are lifted when second-order shifts are included. This can lead to extra lines and/or asymmetric line shapes. The effect was first observed in the spectrum of the methyl radical, CH3, produced by... 

ESR spectrum of the methyl radical, CH3 (note discontinuities in magnetic field axis). Simulated using hyperfine splitting from ref. 3 and eqn (2.5). 

Methyl radicals formed on a silica gel surface are apparently less mobile and less stable than on porous glass (56, 57). The spectral intensity is noticeably reduced if the samples are heated to —130° for 5 min. The line shape is not symmetric, and the linewidth is a function of the nuclear spin quantum number. Hence, the amplitude of the derivative spectrum does not follow the binomial distribution 1 3 3 1 which would be expected for a rapidly tumbling molecule. A quantitative comparison of the spectrum with that predicted by relaxation theory has indicated a tumbling frequency of 2 X 107 and 1.3 X 107 sec-1 for CHr and CD3-, respectively (57). 

The photodecomposition of isopropyl alcohol on silica gel produces a seven-line spectrum having a hyperfine separation of 20.7 G and an amplitude ratio of 1 6.7 20.2 31 21.1 7.4 1.5 (68). This spectrum was attributed to SiOCMe2 formed from the ether surface groups. In addition to this spectrum the spectrum of the methyl radical was also observed. Irradiation of adsorbed tert-butyl alcohol produced a three-line spectrum which was attributed to SiOMe2OCH2 (68). Apparently the splitting from the methyl protons was too small to be observed. 

When ions at m/z 315 are isolated and submitted to CID, the product ion spectrum shown in Figure 2.15(b) is obtained. Productions at m/z 300,297,273 and 269 can be attributed to losses of a methyl radical, water, cyclopropane and formic acid, respectively. These decompositions, together with other information and a more detailed study of the MS [2] spectrum, enable the identification of the compound with [M+H]+ at m/z 315 as proto-nated 7-oxodehydroabietic acid. 

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). 

To select between these two alternative structures it was necessary to synthesize a labeled analog. Three hydrogen atoms of the methyl moiety of the ester group were substituted for deuterium. One of the principal pathways of fragmentation of [M N2]+ ions involves the loss of CH3 radical. Since all R substitutes in diazo ketones 4-1 were also methyls it was important to detect what group exactly is eliminated from the [M N2]+ ion. The spectrum of deuterated sample has confirmed that the methyl radical of the ester moiety leaves the parent ion. As a result the cyclic structure 4-2 was selected as the most probable. The ketene structure 4-3 is hardly able to trigger this process, while for heterocyclic ion 4-2 it is highly favorable (Scheme 5.22). 

The pre-eminent advantage of C-nitroso-compounds as spin traps is that in the spin adduct the scavenged radical is directly attached to the nitroxide nitrogen. Consequently, the esr spectrum of the spin adduct is likely to reveal splittings from magnetic nuclei in the trapped radical, and these will greatly facilitate its identification. A simple example is presented in Fig. 2, which shows the spectrum of the spin adduct of the methyl radical with 2-methyl-2-nitroso-... 

The El mass spectrum of acetone is comparatively simple. It basically shows three important peaks at m/z 58, 43, and 15. According to the formula C3H6O, the peak at m/z 58 corresponds to the molecular ion. The base peak at m/z 43 is related to this signal by a difference of 15 u, a neutral loss which can almost always be assigned to loss of a methyl radical, CH3. The m/z 15 peak may then be expected to correspond to the ionic counterpart of the methyl radical, i.e., to the CH3 carbe-nium ion (Fig. 6.3). The question remains, as to whether this mass spectrum can be rationalized in terms of ion chemistry. Let us therefore consider the steps of electron ionization and subsequent fragmentation in greater detail. 

The molecular ion is relatively abundant (30-50%), as is the (M — ion. The latter may be represented as either (a) or (b) (Scheme 32). The clue which points out unequivocally to an isopavine nucleus is the presence of the (M — 43) + ion in intensities varying from 30 to about 60%. It is formed by the retro-Diels-Alder condensation of the molecular ion, resulting in loss of a CH2=NCH3 unit. This particular ion is practically absent in the spectrum of a pavine (77). An additional peak of moderate intensity is associated with the (M — 86) ion which is formed by a subsequent loss of a methyl radical and carbon... 

An unexpectedly encountered peak in the spectrum of reframidine (27) is due to the (M + 14)+ ion, formed by the transfer of a methyl radical from one molecular ion to another, followed by hydrogen expulsion (77). Furthermore, an (M - 16)+ peak has been spotted in the spectrum of amurensine (24), being attributable to the elimination of a methyl radical from the (M — 1)+ ion (77). The presence of a rather unusual (M — 17)+ peak in the spectrum of amuren-sinine (25) remains unexplained (71). 

The g-value of the methyl radical whose centre of ESR spectrum appears at 329.4 mT in a spectrometer operating at 9-233 G. Hz (h = 6-627 x 1034 Js, electron Bohr Magneton = 9-27 X 1024 JTl) is. The number of lines in the ESR spectrum of this methyl radical predicated ... 

The ESR spectrum of radicals in poly(4-methyl-l-pentene) induced by ultraviolet light 4,5) is composed of a sharp quartet with the hyper-fine splitting constant of 22.5 gauss and a broad quartet. The sharp component has been attributed to methyl radicals (XI) while the broad component could be caused by polymer radicals of structures XXIII and/or XXIV. 

Figure 6 ESR spectrum of methane hydrate irradiated by x-rays at 11 K. Methyl radicals and hydrogen atoms in synthetic methane hydrates (Takeya et al., 2004).,m...

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