LABILITY AND ENERGY IN RELATION TO PROTOPLASM. 397 



nitro-group, however, we observe a somewhat different behaviour 

 in regard to the influence of position ; thus I. 3 dinitropropanc is 

 much less stable than the isomeric I. 1 or 2. 2 dinitropropanes.' 1 ' 

 The stability of a compound against chemical attacks grows with 

 the increase of the number of the CH 2 or alkyl groups. Thus, form- 

 aldehyde enters much more easily into various reactions than its 

 homologues ; acetone dicarboxylic ether is no longer attacked by 

 phcnylhydrazine after two methyl groups have been introduced 

 and it even resists the action of phosphorus pentachloride after 

 four methyl groups have entered. (2) Also the relative position 

 exerts an influence; thus, a "methyl group in para-position in 

 diazobenzene leads to a greater stability than one in ortho-posi- 

 tion.* The 1. 3 keto-aidehydes of the form R-CO-CH 2 -CHO 

 are very unstable and undergo spontaneous condensation, while 

 after the introduction of a second alkylic radical in a — position, 

 a product R — CO — CHR' — CHO results that may even be dis- 

 tilled unchanged/ 4 ' On the other hand we must not omit an excep- 

 tion observed with diazo-propionic ether, which is less stable 

 than diazo-acetic ether/ 5 ' 



CH-COOR CH3-C-COOH 



/\ /\ 

 N=N N=N 



Diazo-acetic ether Diazo-propionic ether 



The readiness with which an atom is replaced by another 

 atom or by a radical, may, ceteris paribus, be considered as a 

 measure of the lability of its position. Thus, the hydrogen atoms 

 in ^-position to a keto or carboxylic group show a higher 

 degree of lability than those in /3 or ^-position/' 0 but still more 

 labile are generally the hydrogen atoms of the amido-group. (h 



( 1 ) V. Meyer, Ber. Chem. Ges. 25, 1709. 



(2) Pi trenko, Chemikerzeitung, I895, p. 1880. 



(3) Hirsch, Ber. Chem. Ges. 24, 325. 



(4) Claisen, I!ayr. Akad. Per. 18905x447. 



(5) Curtius, Ber. Chem. Ges. 23, 3037. 



(6) Very numerous are the observations on \arying lability of hydrogen atoms and 

 their substitutes in the benzene ring. Hydrogen atoms in a high degree of lability 

 are easily attracting atomospheric oxygen (autoxidations). By the vicinity of negative 

 groups as cyanogen, phenyl or carboxethyl, certain hydrogen atoms attached to 

 carbon can acquire in special cases the property of being easily replaced by metals; this 

 state, however, is not a genuine case of lability. 



(7) Also the cyanogen group linked to nitrogen is more labile than when linked to 

 carbon (Ber. 28, 2074). 



