What defines stereoisomers?

Stereoisomers are defined by having the same structural formula but differing in the spatial arrangement of their atoms. This means that while the atoms are connected in the same way (i.e., the same sequence of bonded atoms), they differ in how these atoms are positioned in three-dimensional space.

For example, consider geometric isomers where a molecule could have identical connections but differ in the orientation of substituents around a double bond or a ring structure. Another common type of stereoisomer is optical isomers or enantiomers, which are non-superimposable mirror images of each other due to the presence of chiral centers.

The other options do not accurately capture the definition of stereoisomers. Different molecular formulas would indicate different compounds or isomers instead of stereoisomers. Completely different structures would suggest that they are structural isomers rather than stereoisomers. Lastly, while stereoisomers often exhibit different physical properties and reactivities, they can sometimes share similar properties, which does not define them. Thus, the correct definition emphasizes the identical structural framework alongside a variation in spatial orientation.