Questions: Which of the following structures is MOST stable? cyclobutane cyclopropane cyclohexane cycloheptane

Solution Steps

Cycloalkanes are cyclic hydrocarbons, and their stability is influenced by ring strain. Ring strain arises from angle strain, torsional strain, and steric strain.

• Angle Strain: This occurs when bond angles deviate from the ideal tetrahedral angle of \(109.5^\circ\). Smaller rings like cyclopropane and cyclobutane have significant angle strain because their bond angles are much less than \(109.5^\circ\).
• Torsional Strain: This is due to eclipsing interactions between adjacent hydrogen atoms. Smaller rings also tend to have more torsional strain.
• Steric Strain: This occurs when atoms are forced too close to each other, which is more common in larger rings.

• Cyclopropane: Has significant angle strain because its bond angles are \(60^\circ\), far from the ideal \(109.5^\circ\). It also has high torsional strain due to eclipsing hydrogens.
• Cyclobutane: Has less angle strain than cyclopropane, with bond angles of approximately \(90^\circ\), but still significant. It also has torsional strain.
• Cyclohexane: Can adopt a chair conformation, which minimizes angle and torsional strain, making it very stable.
• Cycloheptane: Larger than cyclohexane, it has more flexibility but can still experience some steric strain and less optimal conformations compared to cyclohexane.

Cyclohexane is the most stable of the given cycloalkanes because it can adopt a chair conformation that minimizes both angle and torsional strain, resulting in a structure with very low overall strain.

Final Answer