Which type of isomers can only change by breaking and reforming covalent bonds?

Configurational isomers, also known as stereoisomers, can only be interconverted by breaking and reforming covalent bonds. This class of isomers involves differences in the spatial arrangement of atoms within a molecule that cannot be altered simply by rotation around single bonds. For instance, in alkene molecules, the presence of a double bond restricts rotation, thus creating two distinct geometric forms known as cis and trans configurations.

To shift from one configurational isomer to another, such as from "cis" to "trans", the double bond must be broken, allowing for a realignment of the atoms before it reforms. This process fundamentally relies on changes that occur at the covalent bond level, whereas other forms of isomers, such as geometric or conformational isomers, undergo interconversion through rotation around single bonds without breaking any covalent bonds.

Structural isomers, on the other hand, differ in the connectivity of their atoms, and their conversion can involve the rearrangement of atomic connectivity but does not strictly require the breaking and reforming of covalent bonds as is the case with configurational isomers.