Radicals ethylene

Resonance theory can also account for the stability of the allyl radical. For example, to form an ethylene radical from ethylene requites a bond dissociation energy of 410 kj/mol (98 kcal/mol), whereas the bond dissociation energy to form an allyl radical from propylene requites 368 kj/mol (88 kcal/mol). This difference results entirely from resonance stabilization. The electron spin resonance spectmm of the allyl radical shows three, not four, types of hydrogen signals. The infrared spectmm shows one type, not two, of carbon—carbon bonds. These data imply the existence, at least on the time scale probed, of a symmetric molecule. The two equivalent resonance stmctures for the allyl radical are as follows ... 

The second case is illustrated in Figure 6, where the total energy dependences on the C—C bond distance in ethylene radical ions are presented. 

HMO Predictions for Dimerization Equilibria of Substituted Ethylene Radical Anions ... 

An accident occurred in a gas pipeline in which the pressure of ethylene radically changed from 1 to 88.5 bar. The explosion which followed caused the gas pipeline to break by increasing the temperature of its walls to 700-800°C. The sudden temperature rise caused by the pressurisation and the fall of temperature at which gas combusts can be another factor (see p. 241). 

The initiator radical reacts with ethylene to yield ethylene radical 1+ CH2 = CH2- -> I - CH2 - CH2... 

In the MS of oxetane the relative abundance of the ethylene radical ion is about eight times greater than that of the formaldehyde radical ion at the usual ionizing potential of 70 eV. However, 2,2-dimethyloxetane fragments much more to the radical ion of acetone... 

The novel four-center two-electron delocalized o-bishomoaromatic species 593, 594,599,601a, and 603 are representatives of a new class of 2jt-aromatic pericyclic systems. These may be considered as the transition state of the Woodward-Hoffmann allowed cycloaddition of ethylene to ethylene dication or dimerization of two ethylene radical cations985 (Figure 3.25, 604). Delocalization takes place among the orbitals in the plane of the conjugated system, which is in sharp contrast to cyclobutadiene dication 605 having a conventional p-type delocalized electron structure (Figure 3.25). 

Dioximes. A group of compds contg two dioxime radicals alpha — Glyoximes beta — Glyoxime Peroxides and gamma — Compounds in which the two oxime radicals are separated by the ethylene radical, such as in succinaldehyde-dioxime, HON CH.CH2-CH2.CH NOH... 

It was confirmed that the fracture of the ethylene monomers at 77 K produced no free radicals. The quintet ESR spectrum shown in Fig. 7.24 can be undoubtedly attributed to the propagating radical of polyethylene, —CpHp2 (Ca ) H 2, when both the polymers and the monomers are simultaneously fractured. The quintet is due to hyperfine splitting of two a- and two fi-hydrogen nuclei. No trace of the Pl FE radical was detected in the observed spectrum. Accordingly the polymerization of ethylene, which was proved by ESR, had been initiated not by the ethylene radicals but by the PTFE mechano radicals at as low a temperature as 77 K. This extremely high reactivity of the radicals is rather surprising because both PTFE and ethylene react in the solid state at 77 K. The mechano radicals newly created by the chain scission are surrounded by the monomer molecules because the radicals are trapped in the fresh surface formed by the mechanical destruction. 

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