Absorption curves of some azo dyes in alcohol

There are other ways in which such an insulation between parts 

Muller and Neuhoff on some more complex substituted diphenyls  

In certain molecules the steric requirements may be such as to reduce the conjugation without completely inhibiting it. In this 

For some of the more complex molecules, in which there exist parts which in themselves contain excellent resonance systems, it is sometimes possible to observe absorption bands which are almost certainly due to oscillations within these parts but somewhat perturbed by the rest of the molecule, together with an absorption band attributable to an oscillation throughout the molecule as a whole. 

This phenomenon of partial oscillation may appear in simple molecules as well, although not quite so readily assignable, and corresponds somewhat to the older ideas of assigning to a particular group a characteristic frequency which may be recognizable in a number of differently constituted molecules, provided they are not too different in their resonance characteristics. 

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Figure 30. Absorption curves of some azo dyes in alcohol.

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