chemist Adolf von Baeyer in 1890. Previously, the only types of strain believed to exist were torsional and steric; however, Baeyer's theory became based on the interactions between the two strains. Baeyer's theory was based on the assumption that the rings in cyclic compounds were flat, and the simple geometry required for atoms in a planar structure.

Around the same time, postulated that rings were not flat, and potentially existed in other folded or twisted conformations. Ernst Mohr