226 SCIENCE PROGRESS 



the two cases appears to be associated with, though not 

 necessarily dependent on, the fact that whilst the hydrogen 

 of the defines is inert and paraffinoid, the compounds now 

 under consideration are characterised by the presence of 

 hydrogen atoms which are displaceable by metals and possess 

 more or less pronounced acidic qualities. Many of these 

 compounds, it is true, are so feebly acidic that they only yield 

 salts by the direct action of metallic sodium, but even this 

 weak acidity appears to be sufficient to bring them into the 

 group of electrolytes and to confer on the displaceable hydrogen 

 atom a degree of mobility which has no parallel in the case 

 of atoms which cannot be thus displaced. 



Four chief types of compounds come into consideration in 

 this group of changes, 1 namely, those in which there is a 

 transference of hydrogen — 



(i) Between carbon and oxygen : in carbonyl-compounds, of 

 which the example most frequently quoted (though by no means 

 the most fully investigated) is ethyl acetoacetate : 



CH,.CO CH 3 .C.OH 



I $ II 



C,H 5 .O.CO.CH., C 2 H 5 O.CO.CH 



Ketonic form Enolic (unsaturated alcohol) form 



and in compounds such as nitrocamphor — 



/CH.N0 2 C:NO.OH 



C 8 H 14 < | $ C 8 H U < | 



\CO \CO 



Normal form Pseudo form 



(ii) Between carbon and nitrogen as in prussic acid — 

 H.C = N =C = NH 



(iii) Between nitrogen and oxygen, as in isatin — 



CO— CO CO — C.OH 



II I II 



C S H 4 .NH C 6 H 4 .N 



or in acetoxime — 



/NH 

 CH 3 .CH:NOH <T CH,.CH< | 



\0 



(iv) Between oxygen and oxygen, as in nitrosophenol 

 (quinone monoxime) — 



HO.C.H..NO ^ = C 6 H 4 =NOH 



1 An exhaustive classification into a score of groups has been made by Laar 



