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

\[\rm{A} + \rm{e}^{-} \rightarrow \rm{A}^{\cdot- }\]	$\quad$(1)
\[\rm{A}^{\cdot- } \rightarrow \rm{B}^{\cdot- }\]	$\quad$(2)
\[\rm{B}^{\cdot- } + \rm{A} \rightarrow \rm{B} + \rm{A}^{\cdot- }\]	$\quad$(3)

An analogous sequence involving radical cations ($\ce{A^{+.}}$, $\ce{B^{+.}}$) is also observed. The most notable example of electron-transfer catalysis is the \(\rm{S}_{\rm{RN}}1\) (or \(\rm{T}+\rm{D}_{\rm{N}}+\rm{A}_{\rm{N}}\)) 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).