Organic Chemistry MCAT Practice Exam 2025 - Free MCAT Practice Questions and Study Guide

The stability of cycloalkanes is primarily influenced by the degree of angle strain present in the ring structure. In cycloalkanes, angle strain arises when the bond angles deviate from the ideal tetrahedral angle of 109.5 degrees due to the geometric constraints of forming a cyclic structure.

For example, in cyclopropane, the bond angles are approximately 60 degrees, which is significantly less than the ideal angle, leading to a high degree of angle strain and making the molecule less stable. As the size of the cycloalkane ring increases, the bond angles approach the ideal tetrahedral angle, thereby reducing angle strain and increasing stability. Cyclohexane, for instance, adopts a chair conformation that minimizes this strain and is highly stable compared to smaller rings.

While the number of substituents, hybridization of carbon atoms, and electronegativity of the atoms in the ring may have roles in certain contexts, they do not directly control ring strain as profoundly as the geometry of the ring itself. Angle strain, as the primary contributor to ring strain in cycloalkanes, is what fundamentally determines their stability.