Pharmacy Curriculum Outcomes Assessment (PCOA) Practice Exam

Epimers are described as:

1. 2 isomers that differ in configuration at only one stereogenic center

2. Molecules with the same formula but different structures

3. Isomers that can interconvert by chemical reaction

4. Isomers with a different arrangement of atoms in space

The correct answer is: 2 isomers that differ in configuration at only one stereogenic center

Epimers are a type of isomers that differ in configuration at only one stereogenic center. This means that the two molecules have the same chemical formula and overall structure, but they have a different arrangement of atoms at one specific point. For example, glucose and galactose are epimers of each other because they both have the same chemical formula but differ in the configuration of their hydroxyl group at C4. Option B is incorrect because isomers are molecules with the same formula but different structures, not just a specific type of isomer. Option C is incorrect because isomers can interconvert by chemical reactions, but this definition applies to all isomers, not just epimers. Option D is incorrect because all isomers, including epimers, have a different arrangement of atoms in space as a defining characteristic. Epimers are specifically differentiated by their single differing stereogenic center.