Stephen E. Stein

Henry H. Storch Award in Fuel Chemistry sponsored by Exxon Research & Engineering Co. STEPHEN E. STEIN has shown how fundamental principles of predictive thermochemistry and kinetics and model compound studies can be used to understand complex coal reactions. In particular, his pioneering research has provided a general framework on which to view coal conversion chemistry and to build mechanistic models. In one set of theoretical studies, Stein, a research chemist in the chemical kinetics division of the National Institute of Standards & Technology (NIST), applied the Hûckel molecular orbital theory to homologous series of benzenoid polycyclic aromatic hydrocarbons (PAHs). This work showed that reactivity depends almost solely on the chemical structures near the reaction site, leading to "an impressive simplification/' as one colleague puts it, of the problem of reactions of complex mixtures of PAHs. In turn, it enables the examination of possible chemical mechanisms for coal gasification. In other such studies, Stein organized the types of reactions and classes of free radicals of probable importance in thermal coal chemistry. In experimental work, Stein and his coworkers measured rate constants needed for predicting the behavior of reacting systems of aromatic and polycylic aromatic molecules. Rate constants for radical disproportionation, for instance, were measured for the first time for hydroaromatic radicals and an unexpected dependence on radical structure was found. More recently, Stein determined the dissociation rates of a large number of substituted anisoles and the effects of various substituents on bond strengths. The result of his theoretical and experimental work has been a much better understanding of carbon growth and -transfer reactions. And it has provided a scientific basis for the idea of active sites as well as a method for estimating energies of reactions at the edges of large PAHs. Stein received a B.S. degree in chemistry from the University of Rochester in 1969, and a Ph.D. degree in physical chemistry from the University of Washington, Seattle, in 1974. He did postdoctoral work and was a research chemist at Stanford Research Institute from 1974 to 1976, and it was during this period that he began his research in coal chemistry. He joined the faculty at West Virginia University in 1976 and moved to NIST in 1982. Stein has more than 50 publications to his credit. He served on the editoral board of the International Journal of Chemical Kinetics from 1976 to 1987. He has been a consultant to Union Carbide and Exxon. 30 October 28, 1991 C&EN