These two products are different from each other. The reason for this is that one of these products does not have a binding between the carbon atoms that carry the substituent group, while the other product has a binding between the carbon atoms that sister the substituent group.
Thus a total of four double-substitution products are possible from the structure of the cake, while a total of three double-substitution products are obtained from benzene.
kekule introduced the kinetic formula of benzene in 1872 to correct this defect of benzene’s structure III. According to the kinetic formula of kekule, benzene ring is an equilibrium mixture of the following two structures, in which these two structures rapidly change into each other.
Since the two Ortho-replacement products rapidly change into each other, they cannot be separated and are considered to be the same product.