xvn MOLECULAR ARCHITECTURE 431 



" These formulae are justified by the reactions. We know, 

 for example, that acetyl-com pounds are resolved, in many 

 cases, into carbonic compounds and methyl compounds : 

 acetic acid can be transformed by heat into carbonic acid and 

 hydride of methyl (marsh gas) ; potassium acetate gives, by 

 the action of an electric battery, methyl * and carbonate of 

 potash etc." (Treatise, 1852, IV. 606). 



Thus in order to express the decompositions represented by 

 the equations 



C 2 H 4 O 2 = CH 4 + CO 2 (decomposition by heat) 



2C 2 H 4 O 2 = (CH 3 ) 2 + 2CO 2 + H 2 (decomposition by electrolysis). 



it was necessary to write acetic acid, not merely as 

 ; 0{ H , but also as O {COW , 



where the ACETYL group, C 2 H 3 O, is shown as a conjugated 

 radical, composed of CARBONYL, CO and METHYL, CH 3 . 



Other decompositions suggested that the acetyl group 

 should be represented as C 2 H 3 (O), i.e. as a compound of 

 a hydrocarbon radical C 2 H 3 with oxygen. In the same way, 

 " even the alcohol-radicals may be considered as conjugated 

 radicals, of which the constituent radicals are the aldehyde 

 radical 2 and hydrogen." Thus whilst acetyl= C 2 H 3 (O), 



The theory of conjugated radicals was also applied 

 effectively to represent nitration-products, obtained by the 

 action of nitric acid on organic compounds such as benzoic 

 acid (ibid. p. 664) ; thus 



Benzoic acid = O /C;H 5 O 



oft 



Nitrobenzoic acid = {C,H 4 (NO 2 )O. 



1 The decomposition of the potassium salt is shown by the equation 

 2C 2 H 3 2 K + 2H 2 = (CH 3 ) 2 + 2KHC0 3 + H 2 . The product, which 

 Gerhardt called methyl, CH 3 , is really dimethyl or ethane, (CH 3 ) 2 or 

 C 2 H 6 . 



2 i.e. C 2 H 3 , aldehyde being (C 2 H 3 )HO. This radical (acetyl 

 minus oxygen) was described by Liebig (see p. 405) as " acetyl." 



