This paper investigates the emergence of conformational analysis in organic chemistry as a case of conceptual change in science. In this case, the mechanism of conceptual change is identified as the emergence of a new exemplar. This new exemplar was made possible because of the identification of a distinctive chemical structure to which ‘foothold’ concepts were applicable. These concepts facilitated both clear explanation in the particular case, and the analogical extension of the conceptual innovation throughout the discipline. The case suggests (...) a cognitive explanation for the importance of exemplars to scientific content. (shrink)