Classification of Clock Reactions

TLDR

Autocatalytic systems are sometimes designated as clock reactions or reactions that exhibit clock behavior. The authors propose a new classification scheme for clock reactions, dividing them into substrate‑depletive, autocatalysis‑driven, and pseudo‑clock systems, to resolve the recent dispute over the term. The classification relies on a full kinetic understanding of the system, enabling assignment to one of the three groups. The scheme successfully categorizes many classical and new reactions, and the authors argue that some autocatalytic processes qualify as clock reactions, though not all do.

Abstract

Autocatalytic systems are sometimes designated as clock reactions or reactions that exhibit clock behavior. To resolve the recent dispute over the term clock reaction, we describe a new approach to classify systems featuring clock behavior into three distinct groups: substrate-depletive clock reactions, autocatalysis-driven clock reactions, and systems that have pseudo clock behavior. Many of the well-known classical and recently discovered reactions can conveniently be put into these categories. We also provide a convincing argument for classifying some autocatalytic processes as clock reactions, but it does not necessarily mean that all autocatalytic processes should be classified as autocatalysis-driven clock reactions. This classification can be conveniently performed if the kinetic nature of the given system has been completely elucidated and understood.