Radical cations, generation from

The chemical pathways leading to acid generation for both direct irradiation and photosensitization (both electron transfer and triplet mechanisms) are complex and at present not fully characterized. Radicals, cations, and radical cations aH have been proposed as reactive intermediates, with the latter two species beHeved to be sources of the photogenerated acid (Fig. 20) (53). In the case of electron-transfer photosensitization, aromatic radical cations (generated from the photosensitizer) are beHeved to be a proton source as weU (54). 

A y-lactone was formed in excellent yield by the nucleophilic cyclization of a carboxylic acid onto an alkene radical cation generated from a (i-nilrophosphale under tin hydride conditions (Scheme 21) [139]. Related experiments employing the acetate group and an internal carboxylate nucleophile failed, emphasizing the very rapid collapse of the alkene radical cation/acetate ion pair [127]. 

In the gas phase, the chemistry of radical cations generated from >C=0 containing species is well-documented, especially in the field of mass spectrometry where a number of diverse and particularly diagnostic processes are known such... 

The structure of diphosphallenic radical cations, generated from the allene ArP=C=PAr by electrochemical oxidation, has been examined using EPR spectroscopy. Ab initio calculations including correlation effects at the MP2 and MCSCF levels have determined that two rotamers exist compatible with Jahn-Teller distortion of the allene.146 Anodically generated radical cations of alkyl phosphites [(RO P] and silylphosphites [(RO)2POSiMe3] reacted with alkenes by initial attack at the C=C bond followed by electron transfer, deprotonation, and elimination of an alkyl or trimethylsilyl cation to form identical alkyl phosphate adducts.147 The electron ionization-induced McLafferty rearrangement of n-hexylphosphine afford the a-distonic radical cation CTEPH, the distinct reactivity of which suggests there is no... 

Spectroscopic studies with photo-CIDNP techniques revealed the existence of two distinct radical cations generated from hexamethyldewarben-zene, presumably rapidly interconverting. In one of these, the central carbon—carbon bond is significantly stretched and bears the unpaired spin density. In the second, the spin density is confined to one of the olefinic bonds. This example is the first to show conclusively that two different radical ion structures can correspond to a single minimum on the ground-state surface of the neutral (Roth et al., 1984). 

A pulse radiolysis study of the reactivity of the radical cations generated from 2-,... 

Polymerization occurs when a radical cation generated from an organic substrate reacts with more than one reactant molecule (monomer) before picking up an electron ... 

A/ -Tosylindole 87 was prepared by the metal-free C—H amination of Af-tosylaniline 86 and DDQ.The reaction is believed to proceed through a radical cation generated from a SET process and a phenonium ion intermediate. Most of the substituted indoles were isolated in very good yields and a variety of aryl, heteroaryl, halogen, and trifluoromethyl substituents were tolerated (14OL3720). 

Role of Water. With increasing water content in acetonitrile the current efficiency for the galvanostatic electropolymerization of thiophene decreases rapidly, but much more slowly for the polymerization of 3-methylthiophene and bithiophene. The competition for radical cations generated from the monomer in the initial electrochemical step between the main reaction (the electropolymerization) and the side reaction (nucleophilic attack of the radical cation by water) explains this decrease in current efficiency [673]. A decrease in the monomer concentration increases the water/monomer ratio and impairs the electrical properties of PT. The presence of water in the electropolymerization process leads to more nonconducting and passivated films [264]. 

Chiral amine catalysts have also been used in cascade reactions mediated by SOMO catalysis [143] and Lewis base catalysis [144]. MacMillan s group developed a powerful cascade reaction moderated by SOMO catalysis. The radical cation, generated from an enamine in condensation of imidazolidinone catalyst 208 with aldehyde 207 and subsequent oxidation by Cu oxidant, was expected to engage in a series of 6-endo-trig radical cyclizations terminated by a suitable arene to give a cyclohexadi-enyl radical. After a second oxidation, rearomatization, and liberation of the catalyst, the requisite 209 would be generated (Scheme 1.90). 

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