Revision - Conformations in Alkanes

Isomerism

Conformations

The different arrangements of atoms in a molecule which can be obtained due to rotation about carbon-carbon single bond are called conformations

To present ocnformations, the diagrams used by chemists a. Saw horse representation and (b) Newman projection can be used.

Conformations of Ethane

Of all the conformations for ethane, only two extreme conformations are important and these are

Staggered conformation
Eclipsed conformation

The staggered conformation is more stable than the eclipsed conformation.

Conformations of Butane

In butane (CH3CH2CH2CH3) the rotation about the single bond between the two inner carbon atoms (C2 and C3) is examined.
The lowest energy conformation will be theo one, in which the two methyl groups are as far apart as possible i.e., 180° away from each other. This conformation will be maximum staggered and is called anti conformation.

Order of stability

Anti>Skew or Gauche>Eclipsed>Fully eclipsed