One-electron reduction

A one-electron reduction in organic chemistry involves the transfer of an electron from a metal to an organic substrate. It serves to differentiate between true organic reductions and other reductions such as hydride transfer reactions that actually involve two-electron species.

The first intermediate in a one-electron reduction is often a radical anion, which then engages in secondary reactions. In the Birch reduction, the secondary reaction is proton abstraction from an alcohol. This reaction type is also called a dissolving metal reduction. Alkyne reduction to an alkene in the liquid ammonia/sodium system follows the same theme. The first radical anion intermediate abstracts a proton from ammonia to the free radical. A second one-electron transfer leads to the anion, which also abstracts a proton to the neutral alkene.

In the Wurtz reaction, two radical intermediates dimerize in a coupling reaction. Likewise, acetone is converted to pinacol with a magnesium-mercury amalgam in a pinacol coupling reaction. Acyloin condensation couples two carboxylic acids to a α-hydroxyketone. Reactions of this type are also called reductive couplings. In the Clemmensen reduction of ketones to alkanes with zinc-mercury amalgam, the intermediate is an organozinc carbenoid.

Electron rich organic molecules like tetrakis(dimethylamino)ethylene (TDAE) are effective reducing agents capable of generating the anion from alkyl halides such as 5-chloromethyl-6-nitrobenzo[1,3]dioxole:^[1]

The one-electron reduction potential of a molecule can be used to obtain an electron affinity. For example: The one-electron reduction potential of molecular oxygen gives a value of 1.07(1) eV.^[2]

References

1. Ouassila Amiri-Attou, Thierry Terme and Patrice Vanelle Molecules (2005). "Functionalization of 6-Nitrobenzo[1,3]dioxole with Carbonyl Compounds via TDAE Methodology" (open access article) 10. pp. 545–551.
2. Chen, Edward C M; Herder, Charles; Chang, Winston; Ting, Regina; Chen, Edward S (2006). "Experimental determination of spin–orbital coupling states of O2(-)". Journal of Physics B: Atomic, Molecular and Optical Physics 39 (11): 2317. Bibcode:2006JPhB...39.2317C. doi:10.1088/0953-4075/39/11/001.