Radical diyls

Divalent and trivalent radicals can be named analogously, using -diyl or -triyl with appropriate locants, or -ylidene or -ylidyne in the case of geminal di- and tri-radicals. 

There is a degree in the continuity and discontinuity of the orbital phase [20]. 2-Oxopropane-l,3-diyl (Scheme 10) is a hetero analog of trimethylenemethane (TMM) where the orbital phase is continuous in the triplet diradical (Sect. 2.1.5) and discontinuous in the singlet diradical (Sect. 2.1.6). The n and orbitals of carbonyl bonds are lower in energy than those of C=C bonds. The lowering strengthens the interaction of the radical orbitals (a, b) with and weakens that... 

Similarly, Hammad and Wenthold have shown that l,4-dicyanocyclohexane-l,4-diyl radical anion forms spontaneonsly upon ionization of 2,5-dicyano-l,5-hexadiene (Eq. 5.13). 3... 

Other selected examples include tris(tetramethylethylene diamine-sodium)-9,9-dianthryl 143,154 alkali metal salts of 9,10-bis(diisopropylsilyl)anthracene 144,155 as well as the closely related naked 9,10-bis(trimethylsilyl)anthra-cene radical anion 145.156 This chemistry is further extended to the solvent-shared and solvent-separated alkali metal salts of perylene radical anions and dianions 146, 147,156 while other examples focus on alkali metal salts of 1,2-diphenylbenzene and tetraphenylethylene derivatives, where reduction with potassium in diglyme afforded contact molecules with extensive 7r-bonding, [l,2-Ph2C6H4K(diglyme)] 148.157 Extensive 7r-coordination is also observed in (1,1,4,4 tetraphenylbutadiene-2,3-diyl)tetracesiumbis(diglyme)bis(methoxyethanolate) 149.158... 

Nitroblue tetrazolium (NBT, 3,3 -(3,3,-dimethoxy-l,l,-biphenyl-4,4 -diyl)bis-2-(4-nitrophe-nyl)-5-phenyl-2H-tetrazolium dichloride) is reduced by superoxide to formazan as a final product, which can be measured spectrophotometrically [73]. Although the rate constant for NBT reduction by superoxide is moderately high 5.88+0.12x 104 1 mol 1 s 1 [74], the formation of formazan is not a simple one-electron transfer process, and the final product is formed as a result of disproportionation of intermediate free radicals. Similar to cytochrome c, NBT is easily reduced by the other reductants that confines its application for superoxide detection. Moreover, similar to epinephrine, NBT free radical is apparently... 

Dai et al. (1990) have reported direct spectroscopic measurements on a similar bishomobenzene radical cation. The system they studied was the bicyclo[3.3.0]octa-2,6-diene-4,8-diyl radical cation [159] generated by radiolytic oxidation of semibullvalene [83] in Freon matrices. The hydrogen... 

The sequential removal of H and H+ from isobutene-type structural units (so-called H2+ abstraction ) was also used to generate the radical anion of non-Kekule benzene , i.e. l,3-dimethylenecyclobutane-l,3-diyl (39) (Scheme 11). As shown by Hill and Squires161, this highly unusual, distonic C(,II(, isomer can be produced in pure form by reaction of O with 1,3-dimethylenecyclobutane (38). Working in a flowing afterglow mass spectrometer, subsequent reactions were again used to characterize this radical anion and differentiate it from other ( VdL, isomers. 

The prototype hole-catalyzed Diels-Alder reaction between the butadiene radical cation and ethylene has also been studied by Bauld [53]. He finds strongly exothermic formation of a l-hexene-3,6-diyl radical cation intermediate without activation energy followed by a weakly activated (activation energy 2.3 kcal mol ) closure of the second C-C bond to form the cyclohexene radical cation, The reaction shows no overall activation energy relative to the... 

The effects of temperature on the shape of intervalence charge-transfer bands for the radical cations of bis(2-f-butyl-2,3-diazabicyclo[2.2.2]oct-3-yl)hydrazines that are bridged by 2,5-xylene-1,4-diyl, durene-l,4-diyl, naphthalene-1,4-diyl, biphenyl-4,4-diyl and 9,9-dimethylfluorene-2,7-diyl aromatic rings were studied by ESR. ... 

The 1,4-diphenylbutane-1,4-diyl biradical (157) was generated from 1,4-dichloro-1,4-diphenylbutane or 2,5-diphenylcyclopentanone under irradiation conditions giving rise to styrene, 1,2-diphenylcyclobutane, and l-phenyl-l,2,3,4-tetrahydronaphthalene. " Tetrahydronaphthalene forms from 1,4-biradicals that have a phenyl group attached to one of the radical centres. Irradiation of 2-phenylcyclopentanone resulted in the formation of tetrahydronaphthalene. 

For example, EPR evidence showed that cyclohexane-1,4-diyl, generated by radiolysis of hexadiene, rearranged to cyclohexene radical cation. Similarly, ant/-5-methylbicyclo[2.1.0]-pentane radical cation (33) rearranged to 1-methylcy-clopentene radical cation (34) via a 1,2-shift of the syn-5-hydrogen. ... 

The suffix ylidene is used to represent radicals such as R-CH. and/or R-CH, and the suffix diyl when the electrons are localised on different atoms. 

The third radical cation structure type is the cyclohexane-1,4-diyl radical cation (22 +) derived from 1,5-hexadiene. The free electron spin is shared between two carbons, which may explain the blue color of the species ( charge resonance). Four axial p and two a protons are strongly coupled (a = 1.19 mT, 6H). + ... 

Radical Chain Deoxygenation of Adenosine 53 by 2 -O-phenoxythiocarbonyt-3, 5 -0-(1,1,3,3-tetraisopropyldlsilox-1,3-diyl)adenosine with TBTH and AIBN [41a]... 

Heterocyclic substituent prefixes generally terminate in -yl for single-bond and -ylidene for double-bond links. Radical prefixes signifying free valencies of more than one ring atom terminate in -diyl, triy./ etc. (the alternative -ylene to -diyl is of no value and could well be discarded). 

Bivalent radicals derived from o/7/io-fused or ortho- and pen-fused polycyclic hydrocarbons by removal of a hydrogen atom from each of two different carbon atoms of the ring are named by changing the ending -yl of the univalent radical name to -ylene or -diyl . Multivalent radicals, similarly derived, are named by adding -triyl , -tetrayl , etc., to the name of the ring system. 

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