If we accept Kekule's formula for the benzene nucleus, then we may expect the double linkages to be opened up partially, either by oxidation or reduction, with the formation of di-, tetra-, or hexa-hydro derivatives, or entirely, with the production of open chain compounds.
Generally rupture occurs at more than one point; and rarely are the six carbon atoms of the complex regained as an open chain.
These compounds retain their aliphatic nature, and are best classified with open-chain compounds, into which, in general, they are readily converted.
Systems which are generally unsaturated compounds, often of considerable stability, and behave as nuclei; these compounds constitute a well-individualized class exhibiting closer affinities to benzenoid substances than to the open-chain series.
Thelfirst four substances are readily formed from, and converted into, the corresponding dihydroxy open-chain compound; these substances are truly aliphatic in character.
