Hydrocarbon structures radical ions

Another type of interaction is the association of radical ions with the parent compounds. Recently (118), a theoretical study was reported on the interaction of butadiene ions with butadiene. Assuming a sandwich structure for the complex, the potential curve based on an extended Hiickel calculation for two approaching butadienes (B + B) revealed only repulsion, as expected, while the curves for B + and B + B" interactions exhibit shallow minima (.068 and. 048 eV) at an interplanar distance of about 3.4 A. From CNDO/2 calculations, adopting the parameter set of Wiberg (161), the dimer cation radical, BJ, appears to be. 132 eV more stable than the separate B and B species, whereas the separate B and B species are favored by. 116eV over the dimer anion radical, BJ. This finding is consistent with experimental results formation of the dimer cation radical was proved in a convincing manner (162) while the attempts to detect the dimer anion radical have been unsuccessful. With other hydrocarbons, the reported formation of benzene dimer anion radical (163) represents an exceptional case, while the dimeric cation radical was observed... 

Of the radical ions derived from aromatic hydrocarbons, we mention the ions of benzene and tetracene. For benzene, both the positive and negative ions have been characterized by ESR spectroscopy. The radical anion shows seven evenly spaced lines ( H = 0.341 mT), ° suggesting that the spin density is distributed evenly over the six carbons (or that there is a fast equilibrium between structures corresponding to the two degenerate antibonding SOMOs Fig. 6.7). Introducing a single D is sufficient to disturb the equilibrium ( h = 0.3983 mT, 4H ah = 0.3454 mT,... 

The dominance of the thermochemically more advantageous decomposition paths is illustrated in Fig. 45 which shows the mass spectrum of paraffin oil (a mixture of liquid paraffins, i.e. of h Mrocarbons of the structure CnH +a) The peculiar alternation of intensities is well-defined. The ions with an odd number of hydrogen atoms possess an even number of electrons and thus are not radical ions. The heat of their formation is lower than that of the ions with neighbouring masses and odd number of electrons, i.e. of radical ions that exhibit the less intense lines. This intensity alternation in hydrocarbon mass spectra, particularly evident for long-chain hydrocarbons, was first reported in [93]. 

The site of reaction on an unsaturated organometallic molecule is not restricted to the most probable position of the metallic atom or cation or to a position corresponding to any one resonance structure of the anion. This has been discussed in a previous section with reference to the special case of reaction with a proton. Although the multiple reactivity is particularly noticeable in the case of derivatives of carbonyl compounds, it is not entirely lacking even in the case of the derivatives of unsaturated hydrocarbons. Triphenylmethyl sodium reacts with triphenylsilyl chloride to give not only the substance related to hexaphenylethane but also a substance related to Chichi-babin s hydrocarbon.401 It will be recalled that both the triphenyl-carbonium ion and triphenylmethyl radical did the same sort of thing. 

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