Theory of chemical structure
1. In an organic compound molecule, the atoms are linked together in the correct valence and in a certain order. That order is called the chemical structure. A change in that bond order, i.e. a change in chemical structure, produces a different substance.
2. In an organic compound molecule, carbon has a valence of 4. Carbon atoms can not only bond with atoms of other elements, but can also bond with each other to form carbon chains (ring, non-ring, etc.) branch, not branch)
3. The properties of substances depend on their molecular composition (nature, number of atoms) and chemical structure (order of bonding of atoms).