A Level Chemistry OCR Practice Exam

What is a key characteristic of a compound that exhibits stereoisomerism?

1. Different molecular formulas

2. Different functional groups

3. Same structural formula with different three-dimensional arrangements

4. Same melting and boiling points

The correct answer is: Same structural formula with different three-dimensional arrangements

A compound that exhibits stereoisomerism is characterized by having the same structural formula but different three-dimensional arrangements of atoms. This means that, despite having the same connectivity of atoms, the spatial orientation of these atoms leads to distinct isomers with potentially different properties. Stereoisomerism typically includes geometric isomerism (cis-trans) and optical isomerism (enantiomers), where the arrangement of groups in space affects the compound's physical and chemical behaviors. For instance, the presence of a double bond or a chiral center can lead to stereoisomers that, even though they are made up of the same atoms connected in the same order, exhibit different spatial configurations. The other options focus on characteristics that do not pertain specifically to stereoisomerism. For example, different molecular formulas would indicate entirely different compounds rather than variations of the same compound, while different functional groups would suggest different types of reactions and properties. Lastly, stating that stereoisomers have the same melting and boiling points is not accurate, as these physical properties can vary between isomers due to their different three-dimensional structures.