Alloisomer is a term used to describe a molecule that has the same molecular formula as another molecule, but a different arrangement of atoms. Synonyms for this term include isomer, stereoisomer, enantiomer, and diastereomer. A stereoisomer is a molecule that has the same atoms arranged in the same order but has a different spatial arrangement due to the presence of one or more chiral centers. An enantiomer is a pair of molecules that are mirror images of each other and cannot be superimposed. A diastereomer is a stereoisomer that is not an enantiomer, meaning they have different spatial arrangements and properties but are not mirror images of each other.