50 Biological Chemistry. 



nitrogen are represented as being " directly " united to a 

 carbon atom. The other typical compounds containing 

 only a single carbon atom, which have been mentioned 

 above, can be graphically represented by the following 

 formulae 



H Cl Cl Cl H 



I I I I \ 



H C H H C H H C Cl Cl Cl and C = O 



Cl Cl Cl Cl H 



The bonds or linkings, as the single lines in the above 

 formulae are called, may be conveniently replaced by dots, 

 thus 0:0:0, H-C : N. 



All the above examples are compounds containing 

 only one carbon atom ; but the conception of the quadri- 

 valency of the carbon atom can also be applied to the 

 representation of compounds containing more than one 

 carbon atom. 



Thus, if the following formulae represent substances 

 with respectively two, three or four carbon atoms, the 

 quadrivalency of the carbon is still maintained. 

 H H H 



H C H H C H H C H 



H H H C H H C H 



H C-H H C-H 



i 



H C H 

 H 



In formulae such as these the carbon atoms are represented 

 as being " directly united " to one another. Now it is 

 possible to lengthen the "chain" of carbon atoms in- 

 definitely and to represent structurally a series of com- 



