Methylene radical, structure

Isomeric Hydroperoxides Formed from Methylene the Structures Contributing to the Group Intermediate Free Radical Resonance Aldehydes Formed by Decom-... 

In the meso and racemic radical structures, the hyperflne coupling constants to the [3-methylene protons are not perturbed greatly by the change in stereochemistry on... 

Herzberg, G. Shoosmith, J. Spectrum and structure of the free methylene radical, Nature 1959,183, 1801-1802. 

The structure in Figure 28 contains information potentially pertaining to translocation of the methylene group of the 5-deoxyadenosyl radical from Co of cobalamin to the substrate 6 A away. The structure shows two conformations of the ribosyl ring in 5-deoxyadenosine, the C2 -endo and the CV-endo conformations. The two conformations project the 5 -methyl group 3.1 and 4.5 A, respectively, from Co. The orientation in the Cy-endo conformation, if replicated in the 5-deoxyadenosyl radical, would allow the methylene radical to... 

The methylene radical offers another surprise the ground state is a triplet, i.e. it contains two unpaired electrons with parallel spins The electronic structure is therefore different from that of CCI2 which, as we have seen, contains a non-bonding electron pair in an sp hybrid AO on the C atom. In the ground state of CH2 one non-bonding electron remains in... 

The starting radical was photochemically generated fh)m a molecule of the corresponding bromide the radical obtained was fixed by the nitroso compound (radical trap). The position of the alkyl radical added to the molecule-trap was established from the EPR spectrum of the formed stable nitroxyl radical. The rate constant is determined by the radical structure and, depending on the number of methylene groups n, it equals (benzene, 313 K)... 

Herzberg, G., The spectra and structure of free methyl and free methylene radical, Proc. Roy. Soc. London Ser. A, 262, 291, 1961. 

Shimizu and Ohtsu [69] have proposed a chemical method to determine head-to-head structures in PVC. Mitani et al. [70] found 2.5-7.0 head-to-head structures per 1,000 monomer units, increasing with the polymerization temperature. It has not been possible to detect internal head-to-head structure by C-NMR spectroscopy with the detection limit of 2 per 1,000 monomer units [71]. Starnes et al. [71] found evidence for the absence of neighboring methylene groups by C-NMR spectroscopy. However, the proposed reaiTangement of head-to-head units at the radical chain ends resulting in chloromethyl branches [Eq. (6)] would partially explain their consumption during polymerization and their absence in the final product. 

Methoxy radical 210 Methyl-de-diazoniation 253 Methylene, energy of triplet state 178 Molecular orbital method, applications to ArNj structure and to dediazoniations - ab initio 84ff., 177ff., 270, 280... 

The (TMS)3SiH mediated addition of phosphorus-centered radicals to a number of alkenes has been investigated in some detail. Reaction (73) is an example of phosphorous-carbon bond formation using four structurally different phenylseleno derivatives with 3 equiv of (TMSlsSiH and AIBN in refluxing benzene for 2h. Comparative studies on the reaction of the four phosphorus-centered radicals have been obtained. Although the reaction with 1-methylene cyclohexane is efficient with all four derivatives, different selectivity is observed with electron-rich or electron-poor alkenes. 

The charged and radical centers may coincide (e.g., elimination of n-electron) or may be separated (e.g., ionization of rr-bond). These centers may be quite far away from one another in the fragment ions. For example, SO2 loss from the molecular ion of tetrahydrothiophendioxide initially leads to a linear chain of four methylene groups, while the charge and the unpaired electron are located at the opposite ends of the chain. Certainly such an ion may further isomerize into a more stable structure. 

The second example depicted in Scheme 3.64 is the trioxotriphenylamine cation-radical. Kuratsu et al. (2005) compared structures of the cation-radical and its neutral counterpart. The neutral compound has a shallow bowl structure, whereas the cation-radical has a planar structure. In the latter, spin delocalization embraces a whole molecular contour, involving the oxygen atoms. This contribntes to the cation-radical stability. (The solid species is easily formed after oxidation of the neutral parent compound with tris(p-bromophenyl)aminiumyl hexafluorophosphate in methylene... 

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