Constitutional isomers are compounds that have the same molecular formula but differ in the connectivity of their atoms. This means that the arrangement of atoms in the molecule is different, leading to distinct chemical and physical properties. For example, C4H10 can exist as two different isomers: butane and isobutane. These variations arise because the atoms can be connected in multiple ways, resulting in different structures. The study of constitutional isomers is important in organic chemistry, as it helps chemists understand how molecular structure influences reactivity and behavior in various chemical reactions.