202 CHEMISTRY 



H 



RN=C/+H-X-+RN=C/ (1) 



X 

 X 



RN=C/+X-CH=NR->RN:C-CH=NR (2) 



X X 2 , 



RN = C-CH=NR + 2H-X^RNH-C-CHX-NHR (3) 



Reversibility of the reactions. The most striking property of the 



X 



addition products of the isonitriles, RN=C^ is their low point of 



Y 



dissociation, i. e., the carbon atom which has absorbed the X Y, 

 thus becoming quadrivalent, is unable to hold XY above certain tem- 

 perature limits. There is consequently in every case a temperature, 

 varying with the nature and mass of X and Y as well as with the 

 nature and mass of the groups bound to the other two affinity units 

 of carbon, at which the carbon atom becomes spontaneously dyad 

 and is unable to remain in a quadrivalent condition; it was subse- 

 quently possible to prove that this is a perfectly general property of 

 this atom. All the addition products under discussion are partially 



X 



dissociated, the dissociation RN = C ^ RN : C< + XY, increasing 



X Y 



as the temperature is raised, in other words the valence of carbon 

 at temperatures below the dissociation-point is an equilibrium phe- 

 nomenon; dynamic equilibrium exists between bivalent and quadri- 

 valent carbon. 



The point of complete dissociation of the various addition products 

 of the isonitriles has not been accurately determined in every case. 

 The following data with reference to the dissociation-points of carbon 

 monoxide addition products are of interest and therefore used for 

 illustration in this connection: 



Dissociation-Point 



Formaldehyde, 0: C=H 2 600 



H 



Formamide, O = C^ about 250 



NH 2 



