Organic molecules are formed by the carbon chains that form the skeletons. The skeletons can have many variations ranging from being straight, branched or arranged in closed rings. Some of the skeletons have double bonds which causes a variance in number and their locations. This variation inside the carbon skeleton is one of the important sources of the molecular complexity as well as the diversity in living matter. Also the atoms of other elements can be bonded to the skeleton at the available sites.
Isomers are one or to more molecules that contain the same atoms with different arrangements.
The molecules are grouped together to form compounds. The difference in the main architecture of organic molecules can be seen in the isomers. Theses compounds have the same molecular formula but different structures therefore different properties. The first type are the structural isomers they are different because the covalent arrangement of their atoms. As the carbon skeletons increase in size.