Staggered Conformation of n-Butane is More Stable than Eclipsed Conformation

The stability of different conformations of organic molecules is determined by the relative energies of the conformations. In the case of n-butane, the staggered conformation is more stable than the eclipsed conformation due to several factors.

1. Steric Strain
In the eclipsed conformation, the carbon-hydrogen bonds on adjacent carbon atoms are in close proximity and experience steric strain. Steric strain occurs when bulky groups or atoms are forced too close together, resulting in repulsive interactions. In the eclipsed conformation of n-butane, the hydrogen atoms on one carbon atom are positioned directly behind the hydrogen atoms on the adjacent carbon atom, leading to significant steric strain.

2. Torsional Strain
Torsional strain arises from the unfavorable interactions between electron clouds of adjacent sigma bonds in a molecule. In the eclipsed conformation of n-butane, the methyl groups on each carbon atom are eclipsing each other, resulting in increased torsional strain. This strain is relieved in the staggered conformation, where the methyl groups are oriented in a staggered arrangement, minimizing torsional strain.

3. Van der Waals Interactions
Van der Waals interactions are attractive forces between non-polar molecules or parts of molecules. In the staggered conformation, the carbon-hydrogen bonds on adjacent carbon atoms are positioned further apart, reducing the potential for unfavorable van der Waals interactions. In contrast, the eclipsed conformation brings the carbon-hydrogen bonds in close proximity, resulting in increased van der Waals interactions.

4. Hyperconjugation
Hyperconjugation is a stabilizing interaction that occurs when the electrons in a sigma bond are delocalized into an adjacent empty or partially filled p-orbital. In the staggered conformation, the methyl groups are positioned in a way that allows hyperconjugation to occur, stabilizing the molecule. However, in the eclipsed conformation, the overlap between the sigma bonds and the adjacent p-orbitals is reduced, resulting in decreased hyperconjugation and decreased stability.

Conclusion
In summary, the staggered conformation of n-butane is more stable than the eclipsed conformation due to reduced steric strain, torsional strain, van der Waals interactions, and increased hyperconjugation. These factors contribute to a lower energy state for the staggered conformation, making it the preferred conformation for n-butane.