The dihedral angle, denoted as θ, is a crucial concept in understanding molecular geometry. It represents the angle of rotation between the two largest substituents attached to adjacent carbon atoms. Specifically, it describes how these groups are oriented relative to each other. For instance, when the two largest groups are perfectly overlapping, the dihedral angle is 0 degrees, resulting in an eclipsed conformation. This conformation is characterized by the highest energy and lowest stability due to the steric strain caused by bulky groups being in close proximity. The repulsion between the electrons surrounding these groups contributes to this instability.

As the dihedral angle increases to 60 degrees, the conformation transitions to what is known as the gauche conformation. In this arrangement, the groups are adjacent but not overlapping, leading to a moderate level of energy and stability—better than the eclipsed conformation but not optimal.

Finally, when the dihedral angle reaches 180 degrees, the two largest groups are positioned directly opposite each other, resulting in the anti conformation. This configuration is the most stable due to the maximum distance between the bulky groups, minimizing electron repulsion and thus representing the lowest energy state.

In summary, the relationship between the dihedral angle and molecular stability is significant: eclipsed (0 degrees) is the least stable, gauche (60 degrees) is moderately stable, and anti (180 degrees) is the most stable conformation.