Question

The staggered form of ethane has__________.

Answer 1

Hint: Staggered form or staggered conformation is a chemical conformation in which the arrangement of atoms or groups of atoms in a molecule results in a \[60^\circ \] dihedral angle. Staggered conformation has a very high stability.

Complete answer:
In ethane, there are seven sigma bonds and rotation about the six carbon-hydrogen bonds does not result in any change in the shape of the molecule. This is because hydrogen atoms are essentially spherical in shape. However, if we rotate about the carbon-carbon bond, then we can obtain different conformations. Among these conformations, only the one having the lowest energy or we can say most stable one will be called the staggered conformation or staggered form. Here, all of the C-H bonds on the front carbon are positioned at dihedral angles of \[60^\circ \] relative to the C-H bonds on the back carbon. Also in staggered conformations, the distance between the bonds (and the electrons in them) is maximized which means that there is very less repulsive force among them.
Hence, we can say that the staggered form of ethane has least repulsive force or least energy or that they are highly stable.

Note:
If the front \[C{H_3}\] group is again rotated by \[60^\circ \], then the ethane molecule goes in the highest energy conformation and eclipsed conformation. Here, the hydrogens on the front carbon are as close as possible to the hydrogens on the back carbon. You should remember that the rotation of a carbon-carbon bond is not completely free. There is a small energy barrier to that rotation. However, the energy barrier is not that high and it only gets noticeable at cold temperatures.