Rotation unimpeded free

Fuchs and Tiganik have devised a formula by which the total moment of a molecule can be calculated if it possesses two separate moments, fn and which are able to rotate freely round certain axes fixed in space. In substituted benzenes, it is possible, by comparing experimental results with the requirements of this formula, to decide whether the rotary power of the polar groups is free or impeded. In m- and p-derivatives, e.g. in the chlorophenols, bromophenols, nitrophenols, etc., essentially unimpeded rotatory power of the OH-dipole round the C—0 bond occurs, while in the o-derivatives, the mutual interaction of the substituents is so considerable that mobility is greatly impeded. There is experimental evidence... 

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