Nonbenzenoid hydrocarbons, reduction

These concepts were recently applied to an understanding of the electrochemical reduction of the mono and dinitro derivatives of the nonbenzenoid hydrocarbon 24a45. Compound 24b exhibits a single one-electron wave at —1.08 V, while dinitro compound 25 exhibits two one-electron waves at —0.88 and —1.05 V46. This behavior is quite similar to that exhibited by ortfto-dinitrobenzene (21) it appears therefore that 25 is reduced to a dianion in which the quinoidal structure 26 is an important contributor to the resonance hybrid. The quinoidal structure 11 could be produced from 25 even though the... 

The electrochemistry of nonbenzenoid hydrocarbons has attracted much interest because their structures offer unusual insights into r-electron systems, which undergo geometric changes upon reduction and obey both the Hiickel An and 4n + 2 rules (Table 2). 

Andersen Jr, A. G. Masada, G. M. 1974 Polarographic reduction potentials of some nonbenzenoid aromatic hydrocarbons. J. org. Chem. 39, 572-573. 

For purpose of description, the electrochemistry of hydrocarbons may usefully be classified in three categories benzenoid, nonbenzenoid, and olefinic hydrocarbons, each of which exhibit characteristic properties upon reduction. 

The electrochemical oxidation of nonbenzenoid unsaturated hydrocarbons is believed to include also the formation of the corresponding radical cation as the first step. However, radical cations derived from alkenes are only in rare cases sufficiently stable to allow for the observation of their reduction back to starting material during CV. Accordingly, the oxidation potentials, such as those listed in Table 2, have in most cases no thermodynamic significance. A notable exception is the oxidation of hydrocarbons of the carotenoid type, which are oxidized in two closely spaced reversible or quasireversible one-electron transfers to the corresponding dications [187,188], and even the quasireversible oxidation to the radical trication has been observed [206]. 

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See also in sourсe #XX -- [ ]

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