Page:Outlines of Physical Chemistry - 1899.djvu/116

 ��OUTLINES OF PHYSICAL CHEMISTRY

�� � �Specific rota-

�Molecular rota-

� � �tion at 20°

�tion at 20°

� � �r i 20 °

�C<°

�Menthol

�- 50-0°

�- 78°

�Menthyl

�formate

�»»

�acetate

�>*

�propionate.

�»>

�n-butyrate

�>»

�n-valerate

�»>

�caproate

�»»

�oenanthate

�>»

�caprylate

� � �'

��Whilst the specific rotation exhibits scarcely any regular progression, the molecular rotation rapidly rises to a maximum, and then remains fairly constant. The esters of borneol, of active amyl alcohol, and of certain acids exhibit the same kind of regularity.

The influence of the^ phenyl (C 6 H 5 ) group is very interesting. For menthyl benzoate, the three menthyl toluates, and the phenacetate and phenylpropionate of the same radical, the following molecular rotations have been found :

��,20 c

��Menthol benzoate ....

�L-~J D

. -236-3°

�„ ortho-toluate.

�. -231-3°

�„ meta-toluate.

�. -2410°

�„ para-toluate.

�., -252-5°

�„ phenacetate.

�. - 190-7°

�„ phenylpropionate.

�. - 161-9°

��From a comparison of these numbers with those of the preceding table we may conclude that in the esters of menthyl the acid radicals only exert an influence on the molecular rotation by that part which is nearest the centre of asymmetry. Because (1) the action of the acetyl radical is just as powerful as that of its higher homologues, and (2) the great influence of phenyl only makes itself felt strongly in the benzoyl- and toluyl-esters (Tchtigaeff, ' Berichte der deut. chem. Gesell.' 1898, page 1778).

�� �