Cyclohexane can exist in several conformations, with the two primary forms being the chair and the boat forms. The chair conformation is more stable than the boat conformation for several reasons:
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Steric Strain: In the boat conformation, there are two hydrogen atoms on the "bow" and "stern" of the boat that are in close proximity to each other, leading to what is called "flagpole interactions." These interactions create steric strain, where atoms are forced closer together than they would ideally prefer, resulting in increased repulsion between electrons.
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Torsional Strain: The boat form has eclipsed bonds, where the hydrogen atoms on adjacent carbons are aligned with each other. This results in torsional strain, which is less favorable than the staggered arrangement found in the chair conformation. In the chair form, all adjacent bonds are staggered, minimizing torsional strain.
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Angle Strain: Though cyclohexane has relatively low angle strain due to its ability to adopt a nearly tetrahedral angle (109.5 degrees), the boat form does create some angle strain compared to the chair form, which maintains those ideal angles.
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Conformational Flexibility: The chair conformation allows for more dynamic flexibility, enabling cyclohexane to move between different chair forms (called chair-chair interconversion) without significant energy barriers. The boat conformation, due to its higher energy, is less favorable and can lead to a preference for the chair form in most conditions.
Overall, the chair conformation is energetically more favorable, making it the predominant form of cyclohexane in solution, while the boat conformation is a higher energy state that is less stable due to steric and torsional strain factors.
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