982 
and is simultaneously under the influence of both the «- and the y- 
carbon atom, which is best symbolised as follows: 
es - iN 
COOR — CH — CH —CH-— COOK 
ee 
In this case the double bond is ‘floating’. In one of the following 
communications | hope to elucidate this formula by a model. 
(In the «e-dialkyl-substituted acids these mobile hydrogen atoms 
are wanting. These acids, in fact, form a separate class where the 
double bond is fixed and thus a pure cis-transisomerism occurs. | 
If an acid belonging to the “mobile class” is dehydrated under 
definite conditions a Aydroryanhydride is formed, namely a deri- 
vative of the a-pyrone: 
SN va 
CH = CH 
If now this hydroxyanhydride is rehydrated in turn the original 
normal acid is generally regenerated, for instance: 
CH — CO CH — cood „CH — COOK 
\\ x | vo he eae 
che © GUC CE 
| / \ Dan ignore 
CH — CC — ox CH — COOK cat eN ONON IE 
Hence, the formation of the normal acid is preceded by that of 
another one, the /abile acid. In some cases — where the hydrogen 
atoms were less mobile, — this labile acid has been successfully 
isolated, namely by hydration of the hydroxyanhydride with an 
excess of strong alkali, or with dilute alkali in presence of casein 
as anticatalyst. 
This labile acid possesses two bonds and, therefore, should be 
obtainable in two forms (cis and trans); this indeed has succeeded 
with g-phenyl-a-glutaconie acid *) so that we now know three iso- 
merides of the acid, which is certainly the most powerful support 
for TrorPe’s conceptions. The other labile acids are, as yet, known 
in one form only; probably (with the exception of the a-benzyl-p- 
methylglutaconie acid) this is always the cis-form. 
1) Soc. 103, 1579. 
