Organic Chemistry MCAT Practice Exam

What type of strain is created by ring systems in organic molecules?

1. Inductive strain

2. Ring strain

3. Resonance strain

4. Stretch strain

The correct answer is: Ring strain

Ring strain is the correct answer because it specifically refers to the strain experienced by cyclic molecules due to bond angle distortions and steric interactions. When ring-shaped compounds are formed, particularly small rings like cyclopropane and cyclobutane, the bond angles deviate significantly from the ideal tetrahedral angle of 109.5 degrees for sp³ hybridized carbon atoms. This deviation causes angle strain, which contributes to the overall ring strain. In larger cycloalkanes, while angle strain may be less significant, torsional strain (which arises from eclipsed interactions between adjacent atoms or groups) and steric strain (from crowding) can still contribute to the overall strain in the ring. The presence of both angle strain and torsional strain in smaller rings leads to a higher energy state, which makes these compounds less stable compared to their acyclic counterparts. In summary, ring strain encompasses the various types of strain experienced by cyclic structures due to their geometric constraints, distinguishing it from other types of strain related to electronic effects or intermolecular interactions.