1528 
As a similar difference in stability has never been notieed in any series 
of cis- and trans-isomerides and, in fact, is not to be expected, this 
result supports to some extent the normal configuration of glutaconie 
acid as figured by THorrr: 
Hooc — ECH — EH — SH — COOH 
=H 
If now in glutaconic acid such a floating double bond is really 
present, this acid (as I already observed in my previous communi- 
cation) will, as regards its properties, not be absolutely connected 
either with the genuine cis-acids or with the trans-acids. We are, 
however, in a position to predict the following with a fairly high 
degree of certainty : 
a. as regards its physical properties this acid will occupy a fairly 
isolated place; 
b. when applying the reactions in whichagenuine cis (respectively, 
a trans) passes into its trans (respectively, cis) isomeride, no change 
will take place here as a rule; 
ce. Tuorpr has succeeded in obtaining from several of the “normal” 
alkyl-substituted glutaconie acids, and also from aconitic acid labile 
modifications (according to THorpy generally real czs-, in two cases 
trans-forms).') Also in glutaconic acid itself these isomerides will 
be capable of existing, though they are sure to be exceedingly labile. 
We may now expect that the ordinary (normal) glutaconic acid, 
when exposed to some chemical action, is first converted into the 
labile modification most favourable for this reaction and reacts in 
this labile form. 
For the purpose of comparing the properties we, of course, want 
instances of pure cis-transisomerism. These we possess in the clas- 
sical isomerism of fumaric and maleic acid, mesaconic and citraconic 
1) Courror, for instance, has recently obtained (C.r. 160. 523 (1915)) from the 
only known benzylindene in which, on account of its mode of preparation and 
properties Turete (Ann. 347. 249), in my opinion, rightly assumes the presence 
of a “floating” double bond, a labile isomeride which is reconverted very readily 
into the well-known ordinary form (for instance, under the influence of alcoholic 
potassium hydroxide.) 
CH Be C Be 
EDS EN : SEs, 
rip eee of en Se > eni Se 
oe ; CH, (ele 
ir ij ‚normaal 
