Methyl radical electron distribution

Loss of a radical can, however, take place in certain circumstances, as exemplified by Methoxsalem. Figure 6.7 shows an ion at miz 202, which corresponds to the loss of 15 Da from mIz 217 MH [32]. In this case, it is the loss of a methyl radical from the methoxy group attached to the conjugated ring system. The resulting radical ion can effectively distribute the lone electron via several canonical forms, thus making the radical loss energetically more favourable. 

Calculate CH bond dissociation energies in propene and in toluene, leading to allyl and benzyl radicals, respectively. (The energy of hydrogen atom is given at right.) Is bond dissociation easier or more difficult in these systems relative to bond dissociation in 3-ethylpentane (methyl CH) Examine spin density surfaces for allyl and benzyl radicals. Draw Lewis structures that account for the electron distribution in each radical. Does spin delocalization appear to stabilize radicals in the same way charge delocalization stabilizes ions ... 

We have spent a good part of this chapter discussing the formation and reactions of the methyl free radical CH3. Just what is this molecule like What is its shape How are the electrons distributed and, in particular, where is the odd electron ... 

More recently Henglein has shown that Ag(CN)2 is reduced at a low rate by radiolytically generated hydroxy methyl radicals [27e]. It was shown that the reduction is much faster when colloidal silver seed particles are present in the solution, resulting in larger silver particles with a narrow size distribution. The reduction occurs on tiny nuclei formed by hydrolysis in solution. The mechanism proposed here involves CH2OH radicals, which transfer electrons to the seed particles, and the stored electrons reduce the Ag(CN)2 directly on the surface of the seeds. Ag(CN)2 was also shown to be rapidly reduced by the organic radicals in the... 

Molecular orbital calculations can be used to model the location of electron density from unpaired electrons in a radical. Open the molecular models on the book s website for the methyl, ethyl, and tert-butyl radicals. The gray wire mesh surfaces in these models represent volumes enclosing electron density from unpaired electrons. What do you notice about the distribution of unpaired electron density in the ethyl radical and rert-butyl radical, as compared to the methyl radical What bearing does this have on the relative stabilities of the radicals in this series ... 

Figure 5 shows the calculated electron density distribution as a slice through the C-H-C linkage of the transition state. Clearly, the H atom has equal electron overlap between the C atom of the parent butane molecule and the C atom of the incoming methyl radical. As such, it can go downhill either way along the energy potential surface. This is an important feature, it keeps the radical alive and therefore makes the chain reaction propagate. 

Exception 1. You will have noticed that all our examples of correct Lewis structures contain an even number of electrons that is, aU are distributed as bonding or lone pairs. This distribution is not possible in species having an odd number of electrons, such as nitrogen oxide (NO) and neutral methyl (methyl radical, -CHs see Section 3-1). 

The radical and ions are exceptionally stable due to resonance the free electron or charge is not localized on the methyl carbon atom but is distributed over the benzene rings. 

Interestingly, one-electron oxidants partly mimic the effects of OH radicals in their oxidizing reactions with the thymine moiety of nucleosides and DNA. In fact, the main reaction of OH radicals with 1 is addition at C-5 that yields reducing radicals in about 60% yield [34, 38]. The yield of OH radical addition at C-6 is 35% for thymidine (1) whereas the yield of hydrogen abstraction on the methyl group that leads to the formation of 5-methyl-(2 -de-oxyuridylyl) radical (9) is a minor process (5%). Thus, the two major differences in terms of product analysis between the oxidation of dThd by one-electron oxidants and that by the OH radical are the distribution of thymidine 5-hydroxy-6-hydroperoxide diastereomers and the overall percentage of methyl oxidation products. 

Frontier electron density distribution for the 3-methylcarbamyl-4-methyl anilinyl radical... 

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