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John Ulric Nef (born June 14, 1862, Herisau, Switz.—died Aug. 13, 1915, Carmel, Calif., U.S.) was an American chemist whose studies demonstrated that carbon can have a valence (i.e., affinity for electrons) of two as well as a valence of four, thus greatly advancing the understanding of theoretical organic chemistry. Brought to the United States by his father, Nef studied at Harvard University (A.B., 1884) and at the University of Munich (Ph.D., 1886), where he...