��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-
�� �a
�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.
�� �
