Every atom-atom map for neutral molecules can be explained by electron pushing diagrams

english

2025

volume 1, issue 1, article p1.01

chemical reaction networks   graph transformations   reaction mechanisms

Univerza na Primorskem
(Obvezni izvod spletne publikacije)

Chemical reactions can be understood as transformations of multigraphs (molecules)that preserve vertex labels (atoms) and degrees (sums of bonding and non-bonding electrons), thereby implying the atom-atom map of a reaction. The corresponding reaction mechanism is often described by an electron pushing diagram that explains the transformation by consecutive local relocations of individual edges (electron pairs). Here, we showthat every degree-preserving map between multigraphs, and thus every atom-atom map, can be generated by cyclic electron pushing. Moreover, it is always possible to decompose such an explanation into electron pushing diagrams involving only four electron pairs. This inturn implies that every reaction can be decomposed into a sequence of elementary reactions that involve at most two educt molecules and two product molecules. Hence, the requirement of a mechanistic explanation in terms of electron pushing and imaginary transition states involving only a small number of bonds does not impose a combinatorial constraint on the feasibility of hypothetical chemical reactions.

24.08.2026