200 
most stable state of the molecule, but all the other. positions will 
also be realized, albeit less frequently, and the more rarely as the 
state deviates more considerably from the most stable. 
Of the «-glycols there are cyclic aeetone-compounds known, 
which are: formed with excess of acetone, to 
O 
aoa ht which a little HCl or H,SO, has been added, 
| C(CH,), and which are stable, when there is not a trace 
rd of these last catalysts present. 
There is every reason to assume that there is 
the greatest chance: that these compounds are formed when the 
OH-groups are situated in the plane with the C-atoms to which 
they are bound, and on the same side of them. When the OH-groups 
repel each other, this will seldom take place, but by taking a very 
great excess of acetone, we shall yet be able to obtain a pretty 
large quantity of the cyclic compound, which can be retained by 
removal of the catalyst, and which can be freed from the acetone 
by fractional distillation. 
When the OH-groups cannot get into the most favourable position, 
or near it, as in some cyclic trans 1.2-diols, where the free rotation 
throngh the ring is prevented, no acetone-compounds will be formed. 
This now has been found, and this renders a firm support to this 
dynamic representation (see below). 
The saturated glycols can, however, always assume the most 
favourable position, thongh it be only rarely; the relative frequency 
of this case may be judged from the state of the equilibrium: 
glycol + acetone z acetone compound + water. 
By determination of the constant of equilibrium: 
Sines x ee 
Zeomnp. x Cu,0 
Ky. = 
a measure is supplied for this frequency, and so also a measure 
for the situation of the hydroxyl groups in the most stable position 
of the molecule. Ë 
Here follows a summary of the constants of equilibrium of some 
glycols: *) 
1) In his thesis for the doctorate (Delft 1919, p. 59) “over de Stereochemie 
der cyclopentaandiolen 1.2 en hydrindeendiolen 1.2”. Mr. CHR. VAN LOON was 
the first to point out that the study of these equilibria would probably bring 
to light minuter differences in the configuration of the molecules than the 
boric acid method. The measurements were carried out by Mr. P. HERMANS. 
