This conception led Kekule to his "closed-chain" or "ring" theory of the constitution of benzene which has been called the "most brilliant piece of prediction to be found in the whole range of organic chemistry," and this in turn led in particular to the elucidation of the constitution of the "aromatic compounds," and in general to new methods of chemical synthesis and decomposition, and to a deeper insight into the composition of numberless organic bodies and their mutual relations.
From this closed chain now follow all the substances which are usually called aromatic compounds.
Having passed in rapid review the various types of compounds derived by substituting for hydrogen various atoms or groups of atoms in hydrocarbons (the separate articles on specific compounds should be consulted for more detailed accounts), we now proceed to consider the closed chain compounds.
The ureides of oxy-acids and dibasic acids form closed chain compounds (see Allantoin; Alloxan; Hydantoin; Purin).
These exercises are usually classified as closed-chain exercise.
