Are chemical isomers emergent?

In discussions of emergence, particularly in chemistry, isomers are often given as an example of an emergent phenomenon. In Anderson's original "More is Different" article, he discussed the chirality of sugar molecules as an example of symmetry breaking. More recently, isomers (and the associated concept of molecular structure) are invoked to justify contentious claims about strong emergence and downward causality.Here, I explain what isomers are and consider whether they are emergent in the sense of novelty, i.e., they have properties that are qualitatively different from their constituents.In a later post, I hope to address the more general and knotty problems of molecular structure and the Born-Oppenheimer approximation.Structural isomersThese occur when a specific collection of atoms (chemical formula) can have more than one molecular structure. An example, shown below, is C3H4.Each structure has different chemical and physical properties. Aggregates of each molecule can have…