Page:Outlines of Physical Chemistry - 1899.djvu/126

 ��OUTLINES OF PHYSICAL CHEMISTRY

��The molecular magnetic rotatory power is an additive property for organic substances. In the same homologous series, its general expression is :

a + nb.

The characteristic a is a special number for the series under consideration, whilst the constant b which corre- sponds to a difference of CH 2, is invariably equal to 1*023 ; n denotes the number of carbon atoms contained in the molecule.

In order that substances follow this rule, it is necessary that they are truly homologous. Isomeric substances, one with a normal carbon chain and the other with side chains, have not the same molecular magnetic rotation.

The following table gives the principal values found for the characteristic a :

��Substances

��Paraffins: ^H^^.

Alcohols: CgHfe+sO

Ethers, simple or mixed.

Aldehydes: C^^O

Ketones ....

Acids : CnH^Oj

Acetic esters starting with ethyl acetate

Ethyl esters starting with ethyl propionate.

Ethyl esters of the succinic acid series.

Chlorides: CJE^Cl.

Bromides: C n H 2n+1 Br

Iodides. ..

Ethyl esters of unsatu-

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�normal

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�normal

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��1SO-

secondary or iso-

��ISO-

»» iso-

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��secondary or iso-

��Abnormal values (too high) have been found for the molecular magnetic rotation of the first two or three members of homologous series, and generally, for sub- stances of low molecular weight.

�� �