Louis Plack Hammett

Louis Plack Hammett (1894-1987) was an American physical chemist regarded as a founder of physical organic chemistry, a term he is credited with coining. Working primarily at Columbia University, where he earned his doctorate and later taught, he developed the Hammett equation, which relates the rates and equilibrium constants of reactions among substituted aromatic compounds to a substituent's electronic effect. He also devised the Hammett acidity function, a scale for comparing the acidity of superacids and other systems too strong for the ordinary pH scale, and gave his name, alongside David Curtin, to the Curtin-Hammett principle governing product ratios from rapidly interconverting reactive intermediates. He wrote an influential textbook that helped define physical organic chemistry as its own field, and his honors included the Priestley Medal in 1961 and the National Medal of Science in 1967.