Methylene derived radical

The reduction of tosylhydrazones can also be performed with sodium borodeuteride in boiling methanol or dioxane, but the mechanism of this reaction (in boiling dioxane at least) is radically different from that of the lithium aluminum deuteride reductions.82 With sodium borohydride the first step is apparently hydride attack on the carbon atom of the C=N bond which is probably concerted with the elimination of the tosylate anion (110 - 111). Migration of the hydrogen from nitrogen to C-3 in (111) concerted with expulsion of nitrogen, provides the corresponding methylene derivative (100).82... 

Table 4. 1H Hyperfine coupling constants [G] for radical cations of quadricyclane, norbomadiene, and their 7-methylene derivatives...

The radical cations of the 7-methylene derivatives, 7-MQ, and 7-MN, also show interesting contrasts [325], illustrating the role of homoconjugation in delocalizing... 

The 3-methylene derivatives of both 2,3-dihydro- and tetrahydro- 4/7-thiopyran-4-ones undergo a radical-promoted addition of alkyl and aryl halides producing 3-substituted thiopyran l-ones (Equations 52 and 53) <1996SL261>. 

Whereas strained ring systems are usually reactive and often unstable, molecules which satisfy the criteria for aromaticity exhibit enhanced stability. As is evident from the structural formula of 1, the cycloproparenes set these features in juxtaposition as they are strained molecules in which a single carbon atom is fused across adjacent centres of an aromatic system. The interest of the experimentalist in strained molecules has been matched by the theoretician in the search for suitable models for developing the concepts of chemical bonding and aromaticity. The cycloproparenes have been particularly important in this regard as they meet the criterion for partial aromatic bond localization and consequent bond length alternation in the aromatic ring as proposed by Mills and Nixon in 1930, viz. la vs lb. The cation 5, anion 6 and radical 7 derived from 1, and also the ketone 8 and exocyclic methylene derivative 9, are of interest in this respect. 

Hexamethylene is so-called because it consists of six methylene (CH2) radicals in combination. It resembles the saturated hydrocarbons in properties. Similar derivatives have been obtained from the homologues of benzene. 

At pH > 10.3, the concentration of RSH relative to RS is small and reaction 4, the hydrogen atom abstraction from RSH by the methylene blue derived radical MB, is a rate limiting factor. If reaction 4, along with the disulfide radical anion formation in reaction 2, are the rate limiting steps in the chain sequence, the reaction would follow the derived rate law shown in Eq. 12. Note that, in terms of the measurable kinetic... 

Finding hydrogen atom abstraction from the thiol is the chain propagating step that produces the chain-carrying thiyl radical rather than electron transfer from a sulfide ion is not unexpected in terms of the expected chemical behavior of the methylene blue derived radical MB. The most probable structure... 

Phenol-formaldehyde resins are produced by a system of chemical reac tions in which the linkage of phenol molecules by meth dene groups plays a predominant part. How ever, because of the rapidity nith Yhich con-ieeutive phenol-formaldehyde reactions usually take place, the isolation d simple methylene derivatives containing onb two or three phenolic nuclei is often extremely difficult. This is particularlj true of phenols in which the active oi tho and para positions are unsubstituted and in which pnups which tend to lower reactivity, such as nitro and carboxyl radicals, are absent. Since in these cases a large number of simple isomeric products can be formed, the separation of any one isomer in a pure state is difficult. The isolation of the simple methylene derivatives is noteworthy, since it clarifies our knowledge of the mechanism by which the more complicated products are produced. 

Bivalent radicals derived from saturated unbranched alkanes by removal of two hydrogen atoms are named as follows (1) If both free bonds are on the same carbon atom, the ending -ane of the hydrocarbon is replaced with -ylidene. However, for the first member of the alkanes it is methylene... 

Bivalent radicals of the form O—Y—O are named by adding -dioxy to the name of the bivalent radicals except when forming part of a ring system. Examples are —O—CHj—O— (methylene-dioxy), —O—CO—O— (carbonyldioxy), and —O—SOj—O— (sulfonyldioxy). Anions derived from alcohols or phenols are named by changing the final -ol to -olate. 

The avermectins also possess a number of aUyflc positions that are susceptible to oxidative modification. In particular the 8a-methylene group, which is both aUyflc and alpha to an ether oxygen, is susceptible to radical oxidation. The primary product is the 8a-hydroperoxide, which has been isolated occasionally as an impurity of an avermectin B reaction (such as the catalytic hydrogenation of avermectin B with Wilkinson s rhodium chloride-triphenylphosphine catalyst to obtain ivermectin). An 8a-hydroxy derivative can also be detected occasionally as a metaboUte (42) or as an impurity arising presumably by air oxidation. An 8a-oxo-derivative can be obtained by oxidizing 5-0-protected avermectins with pyridinium dichromate (43). This also can arise by treating the 8a-hydroperoxide with base. 

Chemical initiation generates organic radicals, usually by decomposition of a2o (11) or peroxide compounds (12), to form radicals which then react with chlorine to initiate the radical-chain chlorination reaction (see Initiators). Chlorination of methane yields all four possible chlorinated derivatives methyl chloride, methylene chloride, chloroform, and carbon tetrachloride (13). The reaction proceeds by a radical-chain mechanism, as shown in equations 1 through. Chain initiation... 

Thermal cycloadditions of butadiene to 3-bromo- 133 and 3-methoxy-5-methylene-2(5//)-furanones 220 were studied (95TL749). These systems contain substituents at C3 capable of stabilizing also a possible radical intermediate, influencing hereby the rate and/or the course of the reaction. Thus, the reaction of 133 and 220, respectively, with butadiene at 155°C afforded mixtures of the expected 1,4-cycloadducts 221 and 222, respectively, and of the cyclobutane derivatives... 

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