XVII 



MOLECULAR ARCEIITECTURE 



427 



Williamson (1852 to 1855) and Odling (1855) on multiple 

 types. Gerhardt's types indicated one stage, but only one 

 stage, in the construction of the molecule of a compound. 



f TT "^ 



Ether, for instance, when written as 2 [ 5 fO> was shown to 



be composed of two ethyl-groups, C 2 H 5 , held together by 

 an oxygen atom ; but no indication was given as to how 

 the atoms of carbon and hydrogen were held together in 

 the ethyl radical. Until the position of every atom in the 

 scheme of combination could be shown, the structure of 

 /the compound was still only partly known. 



The first stage in the subdivision of the compound into 

 .smaller units came through the introduction of "multiple 

 types " and of " mixed types," i.e. of structural formulae 

 ; , showing not one bracket only, as in Gerhardt's simple types, 

 \but two or three brackets, linking together different portions 

 of the molecule. 



MULTIPLE TYPES (as Kekule called them, Ann. Chem. 

 Pharm., 1857, 104, 133) arose primarily from the study of 

 dibasic and of tribasic acids (Williamson, Journ. Chem. Soc. t 

 1852, 4, 352; already quoted on p. 425). Nitric acid, 

 HNO 3 , and potassium nitrate, KNO 3 , could be derived very 

 easily from the simple water type, by writing them as 



N &} 



