Allenic radical

Takemura and Shida54 prepared the allene radical ion by /-radiolysis of halocarbon solid solution of allene at low temperatures and showed that the radical cation has a lower D2 structure than the precursor with a skew angle of 30-40°. Kubonzo and coworkers55 56 produced by /-radiolysis in a low-temperature halocarbon matrix several derivatives of the allene radical cation, i.e. the radical cations of 1,2-butadiene, 3-methyl-1,2-butadiene,... 

Allene Radical Cations. The bimolecular reactivity of the radical reactions of allene and propyne has been a longstanding matter of interest. Myher and Harrison179 studied the ion/molecule reactions of ionized C3H4 with the respective neutral precursor in a medium-pressure chemical ionization source. CsH7+ ions were found to be amongst... 

Grissom, J.W., and Khngberg, D., Tandem enyne allene-radical cyclization via base-catalyzed isomerization of enediyne sulfones, Tetrahedmn Lett., 36, 6607, 1995. 

Fig. 5. The A/B spectrum of the allene radical cation, (a) Experimental results from Ref. 33. (b) 10-mode model from Ref. 34. (c) 15-mode model from Ref. 35. The model spectra are the Fourier Ttansform of the autocorrelation function calculated using the MCTDH wavepacket propagation method. A damping function of t = 50fe has been used.

Fig. 6. The spectrum of the Jahn—Teller split A E state of the allene radical cation using different reduced dimensionality models, (a) A linear 2-mode model including the vibrational modes 02 and or with parameters adjusted to fit the spectrum, (b) A 2nd order 3-mode model including the vibrational modes 02, 03 and vr-...

Fig. 7. The time evolution of state population transfer in the A/B manifold of the allene radical cation after excitation to (a) the B B2) and (b) the X Ey) diabatic state.

Other Reactions of Allenes.— Radical-chain additions to allenes are presumed to involve radical intermediates of allylic structure by initial attack at the central carbon atom or of vinylic structure by attack at the terminal carbons. The extent to which these structures are preferred depends upon structure of starting allene, nature of attacking radicals, and reaction conditions. Addition of toluene-/ -sulphonyl iodide to chiral allenes (cyclonona-1,2-diene and penta-2,3-diene) results in racemic products (376), and hence attack on... 

The vibronic coupling model has been applied to a number of molecular systems, and used to evaluate the behavior of wavepackets over coupled surfaces [191]. Recent examples are the radical cation of allene [192,193], and benzene [194] (for further examples see references cited therein). It has also been used to explain the lack of structure in the S2 band of the pyrazine absoiption spectrum [109,173,174,195], and recently to study the photoisomerization of retina] [196],... 

Polymerization thermodynamics has been reviewed by Allen and Patrick,323 lvin,JM [vin and Busfield,325 Sawada326 and Busfield/27 In most radical polymerizations, the propagation steps are facile (kp typically > 102 M 1 s l -Section 4.5.2) and highly exothermic. Heats of polymerization (A//,) for addition polymerizations may be measured by analyzing the equilibrium between monomer and polymer or from calorimetric data using standard thermochemical techniques. Data for polymerization of some common monomers are collected in Table 4.10. Entropy of polymerization ( SP) data are more scarce. The scatter in experimental numbers for AHp obtained by different methods appears quite large and direct comparisons are often complicated by effects of the physical state of the monomei-and polymers (i.e whether for solid, liquid or solution, degree of crystallinity of the polymer). 

Since the n bonds of allenes are orthogonal, the rates of formation of radicals resulting... 

An analogous stepwise mechanism was also proposed by Wohrle [36] for the cation-radical-initiated cycloaddition of electron-rich allenes with pentamethyl-cyclopentadiene in the presence of tris (p-tolyl) aminium hexafluoroantimonate (TTA SbF6 ) (Equation 1.15). 

Schmittel M., Woehrle C., Bohn I. Radical Cation Initiated Cycloaddition of Electron-Rich Allenes. Evidence for a Stepwise Mechanism. Acta Chem. Scand. 1997 57 151-157... 

Keywords radical cation, stepwise mechanism, electron-rich allenes... 

The groups R2N and Cl can be added directly to alkenes, allenes, conjugated dienes, and alkynes, by treatment with dialkyl-V-chloroamines and acids. " These are free-radical additions, with initial attack by the R2NH- radical ion. " N-Halo amides (RCONHX) add RCONH and X to double bonds under the influence of UV light or chromous chloride. " Amines add to allenes in the presence of a palladium catalyst. ... 

According to Bielski and Allen , since the HO2 radical is of amphoteric character, it will be either protonated... 

Blake, D.R., Allen, R.E. and Lunec, J. (1987). Free radicals in biolr cal systems - a review oriented to inflammatory processes. Br. Med. Bull. 43, 371-385. 

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