Conformational Isomers

• Stereoisomers resulting from a rotation about a single ($\sigma$) bond (usually $C-C$)

Depicting the 3D structure of an organic molecule

wedge and dash depiction of ethane.

However, to effectively illustrate the conformational isomers of ethane it is best to view the molecule along the C-C bond, front to back

Consider the Newman projections for the two conformers of ethane:

angle between two h-c-c-h planes is a dihedral angle: in staggered it is 60 and in eclipsed it is 0

• The staggered conformations represents the lowest energy conformer and is stable (angle = 60)
  • This is because the stearic and electronic effects are minimized

stearic = the conflict between portions of a molecule competing to occupy the same spatial region (spatial contacts between bonds and atoms)

• the eclipsed conformation represents the highest energy conformer and is unstable (angle = 0)

In general, the energetic differences between conformational isomers can be illustrated best with a potential energy diagram, where y = potential energy and x = $\theta$.