Hydrocarbon radical cations bonding

If the hydrocarbon radical cation has a definitive structure, proton loss occurs from one particular, well-defined position and these transformations are more selective than the alternative C-H abstractions from alkanes with radical reagents (Eq. 2). For example, C-H substitutions of the adamantane cage with radical reagents always give mixtures of 1 and 2-substituted adamantanes [2], As the adamantane radical cation (4) has one single structure, proton transfer from the radical cation to the solvent occurs highly selectively. Scheme 2 shows the geometry of 4 and the structure of the complex of the adamantane radical cation with acetonitrile (S) where the tertiary C-H bond is already half-broken. 

Hydrocarbon radical cations, structure and reactivity of, 38, 87 Hydrocarbons, small-ring, gas-phase pyrolysis of, 4, 147 Hydrogen atom abstraction from 0—H bonds, 9, 127 Hydrogen bonding and chemical reactivity, 26, 255... 

By analogy with their behavior in mass spectrometry, branched hydrocarbons are cleaved when oxidized in CH3 CN/TEABF4 at —45 °C. The resulting acetamides of the fragments (Table 6) are formed by cleavage of the initial radical cation at the C,C bond between the secondary and tertiary C atom, to afford after a second electron transfer, carbocations, which react in a Ritter reaction with acetonitrile [29]. 

A review has focused on differentiation between polar and SET mechanisms through kinetic analysis.82 hi two separate reviews, the effects of solute-solvent interactions on electron-transfer reactions have been described.83,84 A review of the behaviour of radical cations in liquid hydrocarbons has given particular emphasis to those with high mobility.85 A paper presents selected studies in the formation of radicals by oxidation with manganese- or cerium-based reagents and then- application to C—C bond formation by SET processes.86... 

In contrast with small and, usually, strained alkanes, the HOMO of polycyclic relatively unstrained saturated hydrocarbons involve several C-C bonds. These hydrocarbons are usually quite reactive toward oxidants and have relatively low JPV values (because of highly-lying HOMO) and IPs (because of substantial delocalization in the radical cations). For example, adamantane elongates several bonds after ionization the C3v form of the adamantane radical cation (4) [12, 13] has three elongated C-C and one long tertiary C-H bond (Scheme 1). 

A similar mechanism (Eq. 4) is operative in reactions of saturated hydrocarbons with closed-shell oxidizing electrophiles (E = Haln+, NOz+, etc.) where the H-trans-fer from a C-H bond is accompanied by an ET through the linearly H-coupled fragment (H-coupled electron transfer) [13]. The hydrocarbon part of the transition structures resembles the respective radical cation (that for the reaction of adamantane with Cl7+ is shown (6) in Scheme 2) [13]. 

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