Ethylene oxide radical cation

It is also worthwhile to compare the ferrocenyl ethylene (vinylferrocene) anion-and cation-radicals. For the cyano vinylferrocene anion-radical, the strong delocalization of an unpaired electron was observed (see Section 1.2.2). This is accompanied with effective cis trans conversion (the barrier of rotation around the -C=C- bond is lowered). As for the cation-radicals of the vinylferrocene series, a single electron remains in the highest MO formerly occupied by two electrons. According to photoelectron spectroscopy and quantum mechanical calculations, the HOMO is mostly or even exclusively the orbital of iron (Todres et al. 1992). This orbital is formed without the participation of the ethylenic fragment. The situation is quite different from arylethylene radical cations in which all n orbitals overlap. After one-electron oxidation of ferrocenyl ethylene, an unpaired electron and a positive charge are centered on iron. The —C=C— bond does not share the n-electron cloud with the Fe center. As a result, no cis trans conversion occurs (Todres 2001). 

In fact, the surface may mediate the requisite chemistry of the initially formed radical cation so that different products can be observed from the same intermediate when generated photoelectrochemically or by other means. The radical cation of diphenyl-ethylene, for example, gives completely different products upon photoelectrochemical activation 2 than upon electrochemical oxidation at a metal electrode or by single electron transfer in homogeneous solution, Eq. (31) . Surface control of... 

Tetrakis(dimethylamino)ethylene (TKDE) is a strong electron donor which oxidizes to radical-cation and dication states similar to the well-known Wurster s radicals. Cyclic... 

Ru(II)tris(bipyridine) [Ru(bpy)3 +] as a photosensitizer, triammonium ethylene-diaminetetraacetic acid [(NH4)3EDTA] as a sacrificial electron donor and the enzyme ferredoxin NADP+ reductase (FDR) [215, 216]. Oxidative electron-transfer quenching of the excited Ru(bpy)3 + yields the A,A -dimethyl-4,4 -bipyridinium radical cation (reduced methylviologen, MV+), which mediates the reduction of NADP+ in the presence of FDR as a biocatalyst (Figure 32A). The quantum efficiency for NADH production corresponds to = 1.9 x 10 . A related system that includes Zn(II)wc50-(A-tetramethylpyridinium)porphyrin (Zn-TMPyP +) as a photosensitizer, mercaptoethanol as a sacrificial donor and lipoamide dehydrogenase (LipDH) as a biocatalyst has been applied for the photochemical reduction of NAD+ to NADH (Figure 32B). 

B-90 and B-91, respectively.390 Another route coupled with cationic ring-opening polymerizations is accomplished for polymer B-92 with the use of a hydroxyl-functionalized initiator with a C—Br terminal, where the OH group initiates the cationic polymerizations of 1,3-dioxepane in the presence of triflic acid.329 Polyethylene oxide)-based block copolymers B-93 are obtained by living anionic polymerization of ethylene oxide and the subsequent transformation of the hydroxyl terminal into a reactive C—Br terminal with 2-bromopropionyl bromide, followed by the copper-catalyzed radical polymerization of styrene.391... 

Other multifunctional initiators include star polymers prepared from initiators via living radical or other living polymerizations. In particular, all of the star polymers via metal-catalyzed living polymerization, by definition, carry a halogen initiating site at the end of each arm, and thus they are potentially all initiators. Thus, star-block copolymers with three polyisobutylene-Mock-PMMA arms and four poly-(THF) -A/oc/F polystyrene or poly(THF)-Woc/c-polysty-rene-Wock-PMMA were synthesized via combination of living cationic and copper-catalyzed living radical polymerizations.381,388 Anionically synthesized star polymers of e-caprolactone and ethylene oxide have... 

The rationale behind this design was justified upon electrochemical investigation of the [2]catenane 184+. This catenane - synthesized in 43% yield (Fig. 26) from crown ether BPP34C10, the bipyridinium dibromide derivative 192+ and ( )-l,2-bis(4,4 -bipyridyl)ethylene - was demonstrated to consist, in solution, of mainly co-conformer A, with the more powerful n-electron-accepting bipyridinium unit located inside the cavity of the crown ether. Upon electrochemical reduction of this bipyridinium unit, the cyclophane undergoes a circumrotational movement with respect to the crown ether such that the profoundly more electron-deficient 7t-extended bipyridinium unit resides inside the cavity of the crown ether, affording co-conformer B. When the bipyridinium radical cation is oxidized back down to its dicationic state, the opposite circumrotational process occurs and the system reverts back to co-conformer A, its ground state [49]. 

The cycloaddition of l,l-bis(2-thienyl)ethylene (prepared in situ from the ethanol (169) with strong electron acceptors such as TCNE or ddq has been shown to proceed via a radical ion pair formed by electron transfer (Scheme 29) <90H(3i)i873>. The reaction with TCNE is rapid and quantitative, taking place at room temperature in 15 min. With ddq, the initial product (170) is further oxidized to (171). When the ethanol (169) is heated alone in the dark at 150°C, it generates the aromatized cycloadduct (173) in 70% yield. Other minor products possibly result from a radical process <91CB1203>. On the other hand, irradiation of the alcohol (169) generates l,l-bis(2-thienyl)ethylene cleanly, which is subsequently transformed to the cycloadduct (172). A radical cation may be implicated in this photochemical [4 + 2] cycloaddition also. 

Cationic surfactants, in contrast to anionic surfactants, usually reduce both the number of particles involved in the polymerization and the rate of polymerization. The nature of the stabilizing emulsifier has a marked effect on the polymerization kinetics. For example, addition of a non-ionic stabilizer [e.g., poly(vinyl alcohol), a block copolymer of carbowax 6000 and vinyl acetate, or ethylene oxide-alkyl phenol condensates] to a seed polymer stabilized by an anionic surfactant decreased the rate of polymerization to 25% of the original rate. The effect was as if the nonionic stabilizer (or protective colloid) acted as a barrier around the seed particles to alter the over-all kinetics. It may be that the viscosity of the medium in the neighborhood of the nonionic surfactant coating of the polymer particle is sufficiently different from that of an anionic layer to interfere with the diffusion of monomer or free radicals. There may also be a change in the chain-transfer characteristics of the system [156]. 

Because of the lower oxidation stability of the EC2 complex compared to the EC-BF4 complex, the oxidation-induced decomposition of EC2 was investigated [36]. While the lowest barrier and most exothermic path yielded CO2 and OC2H3 radical cations, a higher barrier path led to formation of oligo(ethylene carbonate). 

DFT calculations suggest that the doublet-and quartet-spin states of the P450 compound I ferryl porphyrin radical cation are energetically close. According to these calculations, both the doublet and quartet species oxidize ethylene by addition of the ferryl oxygen to one carbon, leaving an unpaired electron on the second carbon of the double bond (Fig. 4.30) [185]. This intermediate radical also exists in doublet and quartet... 

There are also reactive intermediates known as radical cations. The geometries of such species can also be understood using our notions of bonding. One example is the one-electron oxidation of an alkene, where the electron is removed from the tt orbital. For all al-kenes besides ethylene (see Chapter 2 for a discussion of the radical cation of ethylene), oxidation retains a planar structure in the alkene. However, the mixing of the alkyl group s IT-like group orbitals with the now singly occupied tt orbital becomes even more pro-... 

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