PKOXIMATE CONSTITUENTS OF THE ANIMAL BODY 49 



OXY ACIDS are formed by the replacement of one H atom by the group OH. 

 Thus: 



CH 3 



I 

 CHOH is oxypropionic acid or lactic acid. 



I 

 COOH 



KETO-ACIDS. Oxyacids are formed by the oxidation of the group CH 2 or CH 3 

 If at the same time the H 2 group be removed by oxidation a keto-acid may be formed. 

 This is probably the manner in which such acids arise in the body, though it is more 

 usual to regard a keto-acid as the result of oxidation of a ketone. Thus : 



CO CO CO 



I I I 



CH 3 CH 2 .OH COOH 



(acetone) (pyruvic acid 



a keto-acid) 



ACID" AMIDES are formed from a fatty acid by replacing the OH of the COOH 

 group by NH 2 , e.g. : 



CH 3 CH 3 



. | from | 



CO.NH 2 COOH. 



(acetamide) (acetic acid) 



AMINES. These may be regarded as formed from ammonia NH 3 by replacing 

 one or more of the H atoms by an organic radical. Thus we may have : 



CH 3 CH 3 /CH 3 



N^H N(CH 3 N^CH 3 



X H X H X CH 3 



(methylamine) (dimethylamine) (trimethylamine) 



Under the action of living organisms primary amines may be formed from a-amino 

 acids by a process of decarboxylation. Thus : 



CH 3 CH 3 



I I 



CH.NH 2 - C0 2 = CH 2 .NH 2 



COOH 



(a-amino-propionic' acid) (ethylamine) 



AROMATIC COMPOUNDS 



These all contain a nucleus, made up of six carbon atoms, which is extremely stable, 

 so that processes of oxidation, reduction, &c., can be carried out in the compound 

 without destruction of the nucleus. The simplest aromatic compound is benzene 

 C 6 H 6 . It behaves as a saturated compound. It is represented as a hexagon with a 

 hydrogen atom at each angle. 



H 



H 



