Gerhard Ludwig Closs (May 1, 1928 – May 24, 1992) was an American chemist specializing in physical organic chemistry, member of the National Academy of Sciences and the American Academy of Arts and Sciences, chairman of the chemistry department at the University of Chicago.  Closs made seminal contributions in research of the magnetic properties of the intermediate compounds formed in chemical reactions. He is also credited with the discovery that certain reactions polarize atomic nuclei. The National Academies Press called him "one of the outstanding chemists of the post-World War II era". He was also an early leader in the field of carbene chemistry. The New York Times called him "pioneering chemist".
Awards and Distinctions