Radical cations electronic structure

Of course, a close stmctural relationship between radical cations and parent molecules is not likely to hold generally, but it is a fair approximation for alternant hydrocarbons. Deviations have been noted some stilbene radical cations have higher-lying excited states without precedent in the PE spectrum of the parent for radical cations of cross-conjugated systems (e.g., 1) already the first excited state is without such precedent. These states have been called non-Koop-manns states. Alkenes also feature major differences between parent and radical cation electronic structures. 

We will approach radical cation structures according to the nature of the parent molecules, specifically according to the donor type, viz., n-, or o-donors, to which they belong. Among the radical cations derived from rc-donors, those of aromatic hydrocarbons show the closest structural relationship to their parents. They also were the first class to be investigated in detail, because they are comparably stable and their spectra fall into a readily accessible range. This family shows the closest correlation between radical cation AEs, and parent AIs. On the other hand, cross-conjugated systems and alkenes may feature substantial differences between parent and radical cation electronic structures. Hence their tendency towards non-Koopmans type states. 

S. Matzinger and T. Bally, work in progress, 1999. The Dewar Benzene Radical Cation Electronic Structure and the Kinetics of Its Conversion to the Benzene Radical Cation. 

The phenomena enumerated in Section 2.4 do not, of course, fully describe all the differences between chemical and electrode processes of ion radical formation. From time to time, effects are found that cannot be clearly interpreted and categorized. For instance, one paper should be mentioned. It bears the symbolic title ir- and a-Diazo Radical Cations Electronic and Molecular Structure of a Chemical Chameleon (Bally et al. 1999). In this work, diphenyldiazomethane and its 15N2, 13C, and Di0 isotopomers, as well as the CH2-CH2 bridged derivative, 5-diazo-10,ll-dihydro-5H-dibenzo[a,d]cycloheptene, were ionized via one-electron electrolytic or chemical oxidation. Both reactions were performed in the same solvent (dichloromethane). Tetra-n-butylammonium tetrafluoroborate served as the supporting salt in the electrolysis. The chemical oxidation was carried out with tris(4-bromophenyl)-or tris(2,4-dibromophenyl)ammoniumyl hexachloroantimonates. Two distinct cation radicals that corresponded to it- and a-types were observed in both types of one-electron oxidation. These electromers are depicted in Scheme 2-28 for the case of diphenyldiazomethane. 

The vinylcyclopropane radical cation, is another radical cation of structure type B, which is stabilized by conjugation. Its proposed structure was based exclusively on ab initio calculations (B3LYP/6-31G ) because the electron-transfer photochemistry of this species failed to provide clear-cut CIDNP effects [128], In this context it is worth noting that product studies cannot, in principle, establish the cyclopropane radical cation structure type. Irrespective of the structure, nucleophilic capture is expected to result in the cleavage of the strained ring. 

The electron-transfer-induced chemistry of bicyclobutane systems offer a rich variety of reactions. Irradiation of naphthalene in the presence of 46 resulted in rapid fluorescence quenching without rearrangement. In contrast, irradiation with either 1-cyanonaphthalene or 9,10-dicyanoanthracene in solutions containing derivatives of 46 resulted in product formation. The product distribution obtained under electron-transfer conditions is compatible with radical cations of structure type 46 +, which is firmly established by ESR and CIDNP results. Nucleophilic capture of the 1,2,2-trimethyl derivative, 50", led to cleavage of the transannular bond. The initial eapture is followed by net addition, producing 51, or dehydrogenation, yielding 52 [179]. 

Although many radical cation-mediated structural isomerizations on an SC have been documented, isomerizations via a radical anion pathway have not been reported. Potential candidates for such an isomerization would be electron-deficient alkenes or cycloalkanes, as they are more likely to accept conduction-band electrons. 

Radical cations can be derived from aromatic hydrocarbons or alkenes by one-electron oxidation. Antimony trichloride and pentachloride are among the chemical oxidants that have been used. Photodissociation or y-radiation can generate radical cations from aromatic hydrocarbons. Most radical cations derived from hydrocarbons have limited stability, but EPR spectral parameters have permitted structural characterization. The radical cations can be generated electrochemically, and some oxidation potentials are included in Table 12.1. The potentials correlate with the HOMO levels of the hydrocarbons. The higher the HOMO, the more easily oxidized is the hydrocarbon. 

Use geometries, electrostatic potential maps and spin densities to help you draw Lewis structures for butanal radical cation, the transition state and product. Where is the positive charge and the unpaired electron in each Is the positive charge (the unpaired electron) more or less delocalized in the transition state than in the reactant In the product ... 

Fig. 4 Structures of the three-electron hemibonded radical cations [R2S.. SR2] - The S-S bond lengths (HF/6-31G, with the MP2/6-31G values in parenthesis) are given in pm...

Rosenblatt etal have examined the effect of structure and isotopic substitution upon the permanganate oxidation of some alky famines (Table 4). The isotope effect of 1.84 is considered to be sufficiently low to be compatible with aminium radical-cation formation, and it is felt that, while C-H cleavage is significant for oxidation of primary amines, the dominant mode of oxidation of tertiary amines is electron-transfer, e.g. 

Exceeding the limitation of molecular dynamics, the steric requirement of trimethylsilyl groups can cause drastic changes both in structure and of molecular properties of organosilicon compounds. For illustration, the so-called "Wurster s-Blue11 radical ions are selected On one-electron oxidation of tetramethyl-p-phenylenediamine, its dark-blue radical cation, detected as early as 1879 [11a], is gene-... 

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