Answer: They contain different functional groups
They contain different numbers of atoms of each element
The arrangement of the atoms of each element are different in the both compounds
Step-by-step explanation:
When two chemical species contain different atom-to-atom connectivity, different number of atoms of each element, different arrangement of atoms of each element and different functional groups, the both species are actually different compounds as in C2H5OH and C6H12O6.
They undergo different types of chemical reaction because of the different functional groups present in each compound.