396 LABILITY AND ENERGY IN RELATION TO PROTOPLASM. 



discussion of the energy of aldehydes it may be worth while to 

 give a series of cases which show how much various atomic 

 groups and their relative positions can influence the stability of 

 compounds which ranges within very wide limits. ( " While, e.g., 

 certain substances easily resist higher temperatures, as benzene 

 and pyridine, others are decomposed by boiling water, as aceto- 

 acetic acid ; others again change even at low temperatures, as 

 cyanic acid or diamido-acetone. 



As a general rule it may be considered that the increase in 

 number of hydroxy/ or amido-groups, as also the alternation of 

 positive and negative groups, depresses the degree of stability. 

 Glycerol is less stable then propyl alcohol ; di- and triamido- 

 benzenes much less so than mono-amido-benzene i.e. aniline. 

 Diketohexamethylene is less stable than dioxyhexamethylene 

 {Baeyer), and acetoacetic acid less so than pyruvic or acetopro- 

 pionic (lsevulinic) acid ; but it becomes more stable by the intro- 

 duction oi one more carboxylic group. 



CH, 

 I 



CO 

 I 



CH 2 -COOH 



CH,-COOH 

 I 



CO 



I 



CH,-COOH 



Aceto-acetic acid Acetone-dicarboxylic acid (2) 



CH 3 

 I 



CO-COOH 

 Pyruvic acid 



CH 3 

 I 



CO 

 I 



CH, 



CH 2 -COOH 

 Laevulinic acid 



The increase in number of carboxylic groups considerably 

 diminishes the degree of stability in such cases in which two of 

 these groups are linked to the same carbon atom. With the 



(1) In stable chemical compounds the atoms are placed in comparatively fixed posi- 

 tions relatively to each other and a change is not brought about except by relatively very 

 energetic actions. 



(2) The ratio of positive to negative groups is in aceto-acetic acid 2 : 2, while in 

 acetone-dicarboxylic acid it is 2 : 3. This difference may account for the greater stability 

 of the latter. 



