Kenichi Fukui

Kenichi Fukui (1918-1998), Japanese chemist and Nobel laureate. He studied the movement of electrons during chemical reactions and developed a way of predicting how the electrons would behave. For this innovative work, he was awarded the 1981 Nobel Prize in chemistry, which he shared with Roald Hoffmann. Born in Nara, Japan, Fukui Kenichi received his Ph.D. degree in chemical engineering in 1948 from Kyōto University. He taught there for more than 30 years and, after becoming professor emeritus in 1982, also became president of the Kyōto Institute of Technology.

Fukui Kenichi studied benzene (C₆H₆) and its related carbon-based compounds and sought to explain why reactions take place at certain sites on the molecule and not at others. A benzene molecule is made up of carbon atoms arranged in a ring. During a chemical reaction, one or more of the carbon atoms reacts with other molecules—but not in a random way. Depending on the molecules involved and other factors, certain reaction sites are used more frequently than others.

Building on the work of other chemists who were also studying this problem, Fukui Kenichi found that the orbit of electrons around the atom's nucleus held the key to the puzzle. The outermost electrons, or “frontier orbitals,” are those that are involved in the reaction. It is the density of electrons in the outermost orbits—and the corresponding energy levels of these orbits—that influences whether or not a reaction will take place with that particular atom, such as in the carbon atoms of the benzene molecule. Fukui Kenichi supported this theory by calculating energy levels and electron densities for a great many specific reactions—and correctly predicted the behavior of electrons during these reactions.