Di-derivatives x x x p v as $ v as s Here we have assumed the substituent groups to be alike; when they are unlike, a greater number of isomers is possible.

Orientation of Substituent Groups.-The determination of the relative positions of the substituents in a benzene derivative constitutes an important factor in the general investigation of such compounds.

Intermolecular transformations-migrations of substituent groups from one carbon atom to anotherare of fairly common occurrence among oxy compounds at elevated temperatures.

Not only does the substituent group modify the readiness with which the derivative is attacked, but also the nature of the product.

Starting with a monoderivative, we have seen that a substituent group may enter in either of three positions to form an ortho-, meta-, or paracompound.