Staggered conformation

A staggered conformation is a conformation in which groups on adjacent bonded atoms are positioned between the groups on the other atom when viewed along the bond. In the idealized Newman projection of an ethane-like arrangement with three equally spaced groups on each carbon, the rear bonds bisect the angles between the front bonds. This is a geometric description relative to the viewing bond, not a change in molecular connectivity.^[ref]

Put the three front bonds at angular positions $0^{\circ }$, $120^{\circ }$ and $240^{\circ }$ in a Newman projection. Rear bonds at $60^{\circ }$, $180^{\circ }$ and $300^{\circ }$ give a staggered conformation. Rotate the rear group by $60^{\circ }$ and the rear bonds line up with front bonds, giving an eclipsed conformation. These positions describe projections: the atoms are still separated along the central bond.

A simple illustrative potential energy for a threefold rotor iswith torsion angle $\theta$ measured from an eclipsed position. It gives $V(\pi /3)=0$ for a staggered position and $V(0)=B$ for an eclipsed position. Here $B$ is an assumed barrier parameter, not a measured universal constant. Different substituents can give distinct energies to different staggered arrangements, so a geometric label alone is not a complete energy ranking. The historical connection between thermodynamics and hindered methyl-group rotation was examined by J. D. Kemp and K. S. Pitzer.^[ref]