Benzene, alkylation molecular orbitals

With stringent precautions to avoid the presence of water, polycyclic aromatic hydrocarbons show two one-electron reversible waves on cyclic voltammetry in dimethylformamide (Table 7.1). These are due to sequential one-electron additions to the lowest unoccupied molecular n-orbital [1]. Hydrocarbons with a single benzene ring are reduced at very negative potentials outside the accessible range in this solvent. Radical-anions of polycyclic aromatic hydrocarbons [2] and also alkyl benzenes [3] were first obtained by the action of alkali metals on a solution of the hydrocarbon in tetrahydrofuran. They have been well characterised by esr spectroscopy. The radical-anions form coloured solutions with absorption bands at longer wavelength than the parent hydrocarbon [4,5]. 

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