Organic chemistry provides fertile ground for scholars interested in understanding the role of non-linguistic representations in scientific thinking. In this discipline, it is plausible to think of textual representation as supplementing theories whose principle expression is diagrammatic. Among the many sorts of diagrams employed by organic chemists, structural formulas are the most important. In this paper, by examining two central episodes in the development of structural formulas -- Kekulé’s proposal of a structure for benzene and Ingold’s explanation of dipole moments in terms of ‘mesomerism’ – I investigate how the norms for the production and interpretation of structural formulas evolve in response to experimental results. I conclude that one principle way in which structural formulas embody the theory of organic chemistry is through these evolving norms
