Page:Outlines of Physical Chemistry - 1899.djvu/122

 102 OUTLINES OF PHYSICAL CHEMISTRY

Angelic and tiglic acids,

iand J

•CO2H CH3.C.CO2H

Similar examples are oleic and elaidic acids, erucic and brassic acids, &c.

We have now become acquainted with two causes of stereo-chemical isomerism : the asymmetry of the carbon atom, and double linkage between tw"o carbon atoms. These two causes may produce very interesting combined effects in polymethylene ring compounds. Let us take as example the ring of six carbon atoms. Hexamethylene or benzene hexahydride has the formula C 6 H 12 and the con- stitution : jj

/\

\ /

c

The replacement of two of the hydrogen atoms (attached to different carbon atoms) gives rise to the ordinary ortho-,meta-,para- isomerism and besides to stereo- chemical isomers. We know two hexahydroterephthalic acids, a cis and a trans modification :

H C0 2 H H C0 2 H

v v

/ \ /\

��.A A

\/ \/

c c

/ \ / \ •

H C0 2 H C0 2 H H

cto-hexaliydroterephthalic acid. <ran*-hexahydroterephthalic acid.

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