ON THE FUNDAMENTAL CONCEPTIONS UNDERLYING 

 THE CHEMISTRY OF THE ELEMENT CARBON 



BY JOHN ULRIC NEP 



[John Ulric Nef, Professor of Chemistry, and head of the Chemical Department, 

 University of Chicago, b. Herisau, Canton Appenzell, Switzerland, June 14, 

 1862. A.B. Harvard, 1884; Ph.D. Munich, 1886; Kirkland Fellow, Harvard, 

 1884-87. Professor, Purdue University, 1887-89; Assistant Professor, Clark 

 University, 1889-92; Professor,University of Chicago, since 1892. Member of 

 American Academy of Arts and Science, National Academy of Sciences, Royal 

 Society of Science, Upsala, Sweden.] 



Two fundamental conceptions underlie our present system of 

 carbon chemistry. First, the idea of the constant quadrivalence 

 of carbon, which explains most adequately the existence of the vast 

 array of carbon compounds. Second, the conception of substitution 

 or metalepsis, which gives us a basis for interpreting many of the 

 reactions shown by these substances. 



These ideas are, however, in the light of investigations of the past 

 twenty years, inadequate; they must be replaced by the conception 

 of a variable valence of carbon and by the conception of dissociation 

 in its broadest sense. A rigid application of the latter conception 

 gives a far simpler basis for interpreting all the reactions of carbon 

 chemistry; they are naturally also applicable to the chemistry of 

 all the other elements. 



I. On the Valence of the Carbon Atom 



The progress of organic chemistry since 1858 is due chiefly to the 

 development of a few very simple ideas concerning the valence of 

 the elements, ideas which were first clearly and fully presented at 

 that time by Kekule. 



Hydrogen, oxygen, and nitrogen are the elements which most 

 frequently combine with carbon to form the so-called organic com- 

 pounds. Since the compounds of one atom of oxygen, nitrogen, or 

 carbon with hydrogen possess the empyrical formulae, O =H 2 , N = H 3 , 

 C=H 4 , the conception naturally presents itself that the capacity 

 of the various elements for holding hydrogen atoms varies. Oxygen 

 is capable of holding two such atoms, nitrogen holds three, and car- 

 bon four atoms of hydrogen. 



Therefore we assume, taking hydrogen as our unit, that the valence 



I 

 of the element oxygen is two, O , of nitrogen, three, N , and 



I 

 of carbon, four, C . 



