C=C bonds would show aromatic properties was first stated clearly by Doering in a 1951 article on tropolone. Tropolone had been recognised as an aromatic molecule by Dewar in 1945. In 1936, Hückel developed the theory of π-conjugated biradicals (non-Kekulé molecules). The first example, known as the Schlenk-Brauns hydrocarbon, had been discovered in the same year. The credit for explaining such biradicals is usually given to Christopher Longuet-Higgins in 1950. In 1937 Hückel refined his MO theory of pi electrons in unsaturated organic molecules. This is still used occasionally as an approximation, though the more precise PPP Pariser–Parr–Pople method succeeded it in 1953. "Extended Hückel MO theory" (EHT) applies to both sigma and pi electrons, and has its origins in work by William Lipscomb and Roald Hoffmann for nonplanar molecules in 1962. Poem about Schrödinger According to Felix Bloch, Erich Hückel "incited and helped" the students at the University of Zurich to write poems about their great professors. The poem about Erwin Schrödinger went like this: Gar Manches rechnet Erwin schon Mit seiner Wellenfunktion. Nur wissen möcht' man gerne wohl Was man sich dabei vorstell'n soll. It was freely translated by Felix Bloch: Erwin with his psi can do Calculations quite a few. But one thing has not been seen: Just what does psi really mean? Awards 1965 Otto Hahn Prize for Chemistry and Physics References Further reading E. Hückel, Ein Gelehrtenleben: Ernst u. Satire (1975 ). A. Karachalios, Erich Hückel (1896 –1980): From Physics to Quantum Chemistry (Springer, 2010 ). 1896 births 1980 deaths 20th-century German physicists German physical chemists Members of the International Academy of Quantum Molecular Science Foreign Members of the Royal Society Theoretical chemists Scientists from Berlin