The term indicates a sequence of reactions such as shown in equations (1)–(3), leading from A to B :

$$\text{A}+{\text{e}}^{-}\to {\text{A}}^{\cdot -}$$	(1)
$${\text{A}}^{\cdot -}\to {\text{B}}^{\cdot -}$$	(2)
$${\text{B}}^{\cdot -}+\text{A}\to \text{B}+{\text{A}}^{\cdot -}$$	(3)

An analogous sequence involving radical cations (A⁺·, B⁺·) is also observed. The most notable example of electron-transfer catalysis is the ${\text{S}}_{\text{RN}}1$ (or $\text{T}+{\text{D}}_{\text{N}}+{\text{A}}_{\text{N}}$) reaction of aromatic halides. The term has its origin in a suggested analogy to acid-base catalysis, with the electron instead of the proton. However, there is a difference between the two catalytic mechanisms, since the electron is not a true catalyst, but rather behaves as the initiator of a chain reaction. 'Electron-transfer induced chain reaction' is a more appropriate term for the situation described by equations (1)–(3).