ABSTRACT
This chapter examines the circumstances surrounding the appearance of both J. H. Van 't Hoff's and J. A. Le Bel's 1874 papers, and also examines their arguments, focusing on the differences and similarities between their approaches for ascertaining the spatial characteristics of molecules. For the first time, Van 't Hoff supposed that 'arrangement' could mean spatial arrangement, instead of merely the sequence of connections between atoms, and that spatial arrangement was directly related to the structural formulas, which became iconic images. Van 't Hoff's use of paper models was then a direct continuation of the tradition begun during the 1860s, with the important innovation that his models were intentionally iconic, meant to mimic directly certain physical characteristics of the molecule. Le Bel introduced the tetrahedron by arguing from the possible symmetries or asymmetries in the molecular type, not from a concern with accounting for or predicting cases of isomerism.
