Ethane radical cation

C2H6) ethane radical cation or ethane radical ion( +)... 

Figure 6.9. Top to bottom Two possible Jahn-Teller distorted geometries for the methane radical cation and calculated geometry for its energy minimum schematic representation of the SOMO for ethane radical cation SOMOs of three different propane radical cations observed by ESR the SOMO of butane radical cation and SOMOs for two conformers of pentane radical cation.

The ethane radical cation state sequence, X(2Eg) < A(2Ag) < B(2EU) < C(2AU), is well established from its repeatedly recorded PE spectrum3-5 (Figure 3). Both Jahn/Teller distortions of 0.7 eV and 0.8 eV, respectively, and the ionization into the predominantly ffcc-bonding M state A(2Ag) is located at about 13.4 eV in between them. 

The ESR spectrum of ethane radical cation at 4 K in SFe contained a 1 2 1 triplet because of two strongly coupled protons (15.25 mT), corresponding to a spin-... 

Figure 4. Schematic representation of the SOMO for ethane radical cation.

A preparative method for the synthesis of benzo[2,l- 3,4V]bis(l,2,3-thiaselenazole) 31 was reported (Scheme 49) <2001IC4705>. When the dihydrochloride of diaminobenzenedithiol 315 and 2 equiv of SeCL s heated in dichloro-ethane, the crude radical cation salt [31] [Cl] is formed. Reduction of the radical cation salt with triphenylantimony affords neutral product 31 in 13% yield from compound 315. 

The third class of organic donor molecules are a-donors, viz., alkanes and cycloalkanes. These substrates have inherently high ionization and oxidation potentials. Therefore, their radical cations are not readily available by photoinduced electron transfer, but typically require radiolysis and electron impact in the condensed phases or the gas phase, respectively. Thus, radical cations of simple alkanes (methane [206], ethane [207]) or unstrained cycloalkanes (cyclopentane, cyclohexane) [208] were identified and characterized following radiolysis in frozen matrices. In contrast, strained ring compounds have significantly lower oxidation potentials so that the radical cations of appropriate derivatives can be generated by photoinduced electron transfer. 

Among the electron transfer induced reactions of cyclobutane systems, cycloreversions are the most prominent. These reactions are the reverse of the cycloadditions discussed in Sect. 4.1. The reactivity of the corresponding radical cations depends on their substitution pattern. We have mentioned the fast two-bond cycloreversion of quadicyclane radical cation as well as the ready ring closure of a tetracyclic system (3, Sect. 4.1). A related fragmentation of cis-, trans-, cis-1,2,3,4-tetraphenylcyclobutane (84) can be induced by pulse radiolysis of 1,2-dichloro-ethane solutions. This reaction produces the known spectrum of trans-stilbene radical cation (85) without a detectable intermediate and with a high degree of... 

Diaminobutane gives rise to a strain free six membered ring radical cation, and this substance therefore quenches more efficiently than diaminopropane or -ethane. Consequently, monoamines form open chained species after electron transfer. The... 

FIGURE 3. (a) Comparison of the He(I) PE spectra of the >3d-symmetric molecules ethane and disilane, which exhibit Jahn/Teller splitting (J/T) of their M (e) states with dominant contributions ( ) to positive hole delocalization, based on their quantitative radical cation state assignment (see text), (b) United Atom correlation for the isoelectronic 18-electron species from Ar to SiFLj including the iso(valence)electronic 10-electron molecule CH4 with average atomic ionization energies... 

The reductive elimination of ethane from [Cp Rh(PPh3)Me2] was found to be increased by a factor of at least 3 x 109 upon oxidation to the 17-electron radical cation.157 The absence of solvent effects on the rate was interpretated to indicate direct elimination from the cation to give ethane and a 15-electron intermediate, which is rapidly trapped by solvent. 

Fig. 9 Reaction pathways for the cycloaddition of the 1,3-butadiene radical cation with ethane. Results from QCISD(T)/6-31G //QCISD/6-31G calculations in plain text,42a results from UCCSD(T)/DZP//UMP2/DZP in italies.42b,c Numbers in brackets indicate the number of additional minima in the pathway.

Figure 7. Hyperfine coupling constants (mT) of the in-plane chain-end H nuclei for extended

The mechanistic scenario outlined above finds support in the reactivity pattern observed with ethane [20]. The radical cation formed from ethane by electron transfer would be expected to fragment some of the time by C-C cleavage (Scheme 2). The direct precedent for such a step is Olah s observation of CH3N02 as the principal product in the reaction of ethane with N02+PF6 [23]. Indeed, the formation of CH30S03H was observed (up to 25% yield relative to oxidant) when ethane was contacted at 150-180°C in 98% sulfuric acid with any one of a number of radical initiators. 

C-C Bond Strengths in Ethane and Hexafluoroethane and in their Radical Cations... 

In a related way, one can define the C-C bond strengths of the radical cation of the parent and perfluorinated ethanes by the use of equation (2)... 

Two papers have been published which examine the electron transfer sensitised photochemistry of 1,2-polyaryl substituted ethanes.Irradiation of solutions of 1,4-dlcyanobenzene in polar solvents containing the ethanes yields the radical cations of the ethane by electron transfer to the sensitlser. Carbon-carbon bond cleavage in the radical cation produces benzyl radical and benzyl carbocatlon. By examination of the reaction products it is then possible to determine which of the benzyl fragments take the charge and hence obtain estimates of the relative oxidation potentials of a series of benzyl radicals. 

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