That same year, based on observations that Woodward had made during the B synthesis, he and Roald Hoffmann devised rules (now called the Woodward–Hoffmann rules) for elucidating the stereochemistry of the products of organic reactions. Woodward based his ideas on his experiences as a synthetic organic chemist; he asked Hoffman to perform theoretical calculations to verify the ideas. This was done using Hoffmann's Extended Hückel method. The predictions of these rules were verified by many experiments. Hoffmann shared the 1981 Nobel Prize for this work along with Kenichi Fukui, a Japanese chemist who had done similar work using a different approach. Woodward had died two years before and so was not eligible to share this Prize.