Draw Sawhorse projection for the eclipsed and staggered conformations of ethane. Which of these conformations is more stable and why?

To understand the conformations of ethane, we first need to visualize its molecular structure. Ethane (C2H6) consists of two carbon atoms bonded together, with each carbon atom also bonded to three hydrogen atoms. The way these atoms are arranged in space can significantly affect the stability of the molecule. Let's delve into the sawhorse projections for both eclipsed and staggered conformations of ethane, and then discuss which one is more stable and why.

Sawhorse Projections Explained

A sawhorse projection is a way to represent the three-dimensional arrangement of atoms in a molecule on a two-dimensional plane. In this projection, the molecule is viewed from an angle, allowing us to see the relative positions of the atoms more clearly than in a simple line-angle formula.

Eclipsed Conformation

In the eclipsed conformation of ethane, the hydrogen atoms on one carbon are directly aligned with the hydrogen atoms on the adjacent carbon. This arrangement can be illustrated in a sawhorse projection as follows:

• Imagine the two carbon atoms in the center.
• The hydrogen atoms on each carbon are positioned directly behind one another.

This results in a higher energy state due to increased steric hindrance and torsional strain, as the electron clouds of the overlapping hydrogen atoms repel each other. This conformation is less stable due to these repulsive interactions.

Staggered Conformation

In contrast, the staggered conformation has the hydrogen atoms on one carbon positioned between the hydrogen atoms on the adjacent carbon. In a sawhorse projection, this looks like:

• The two carbon atoms are still in the center.
• The hydrogen atoms on one carbon are staggered relative to those on the other carbon.

This arrangement minimizes the repulsion between the hydrogen atoms, leading to a lower energy state. The staggered conformation is more stable because it allows for optimal spacing between the electron clouds of the hydrogen atoms, reducing torsional strain.

Comparing Stability

When comparing the two conformations, the staggered conformation is favored due to its lower energy and reduced steric hindrance. The eclipsed conformation, while possible, is less stable because of the increased repulsion between the overlapping hydrogen atoms. This concept can be likened to two people trying to stand too close together; they would feel uncomfortable and would prefer to stand apart, just like the hydrogen atoms in the staggered conformation.

Conclusion on Stability

In summary, the staggered conformation of ethane is more stable than the eclipsed conformation due to lower energy and reduced steric strain. Understanding these conformations is crucial in organic chemistry, as it lays the groundwork for more complex molecular interactions and reactions.