Alkanes contain carbon-carbon sigma (σ) bonds . Electron distribution of the sigma molecular orbital is symmetrical around the internuclear axis of the C−C bond which is not distributed due to rotation about its axis . This permits free rotation about C−C single bond. This rotation results into different spatial arrangements of atoms in space which can change into one another. Such spatial arrangements of atoms which can be converted into one another by rotation around a C−C single bond are called conformations or conformers or rotamers. Alkanes can have infinite number of conformations by rotation around C−C single bonds. However, it may be remembered that rotation around a C−C single bond is not completely free . It is hindered by a small energy barrier of 1−20kJmol−1 due to weak repulsive interaction between the adjacent bonds. Such a type of repulsive interaction is called torsional strain.