Jordan's early work on the physical chemistry of nucleic acids in solution tin collaboration with the late professor Gulland) led to pioneering conclusions about the hydrogen-bonded structure of native deoxyribose nucleic acid, and about the changes in molecular configuration ('denaturation') that result from interference with this hydrogen bonding. These discoveries laid the foundations for the now accepted helical, hydrogen-bonded structure. He has remained active in this field, contributing particularly to the relationship between stability and chemical constitution; he is actively engaged on the study of the interferences with structure brought about by the binding of small molecules. He has made significant contributions also in the field of synthetic polymers, particularly to the knowledge of the mechanism of ionic polymerisation and to the properties in solution of ionic polymers. He has built up in Adelaide a lively and capable group working on various aspects of the physical chemistry of macromolecular substances, including proteins; this group has owed much to his guidance. He has always taken an active part in the scientific life of Australia, and has been chosen for two important roles outside the University of Adelaide. His active interest in scientific education, in schools as well as in universities, has contributed to the rising standards of Australian chemical graduates.