Conformations:
Conformations are different spatial arrangements of atoms or groups attached to carbon atoms bonded by single bond which arise due to rotation about the single bond. These arrangements are also called conformational isomers or conformers. e.g. ethane (CH3-CH3).
The Newman projection formulas for the conformations of ethane could be depicted as in fig bellow:
The different conformations of ethane are not equal stability. The staggered form in which the hydrogen atoms are perfectly staggered is the most stable conformation. This can be explain in terms of repulsive interactions between bonding pairs of electron. In ethane, the interaction of bonding pairs of electrons (C: H) resulting in tetrahedral structure because it allows maximum separation of the four C—H bonds. The staggered conformation of ethane permits maximum possible separation of the electron pairs of the six C—H bonds. Thus staggered conformation of ethane is most stable and has lowest potential energy.
In the eclipsed conformation of ethane, the hydrogen atoms attached to each carbon are in direct opposition to each other. This permits minimum separation of the electrons of the six C—H bonds. The eclipsed conformation is, therefore, of highest energy and has the lowest stability.
Evidently, all the skew form of ethane will have stabilities in between that of staggered and eclipsed conformation. Hence, the relative stabilities of the various conformations of ethane are:
Staggered > skew > eclipsed