Name: Structure of Benzene
Uploaded: 2019-07-19
Duration: 3 min 53 s
Description: Benzene is the most commonly known aromatic compound and is a significant part of gasoline. In this video, we will study the structure and properties of benz...

Question

Write the possible conformations of ethane and explain which is more stable.

Accepted Answer

In ethane two particular conformers are noteworthy and have special names. In the eclipsed conformation, the $C - H$ bonds on the front and back carbons are aligned with each other with dihedral angles of $0$ degrees. In the staggered conformation, the $C - H$ bonds on the rear carbon lie between those on the front carbon with dihedral angles of $60$ degrees.

Energetically, not all conformations are equally favoured. The eclipsed conformation of ethane is less stable than the staggered conformation by $3 kcal / mol$ . The staggered conformation is the most stable of all possible conformations of ethane, since the angles between $C - H$ bonds on the front and rear carbons are maximised at $60$ degrees. In the eclipsed form, the electron densities on the $C - H$ bonds are closer together than they are in the staggered form. When two $C - H$ bonds are brought into a dihedral angle of zero degrees, their electron clouds experience repulsion, which raises the energy of the molecule. The eclipsed conformation of ethane has three such $C - H$ eclipsing interactions, so we can infer that each eclipsed $C - H$ "costs" roughly $1 kcal / mol$ .

Staggered conformation is more stable than eclipsed because in eclipsed conformation the hydrogen atoms are nearer and repel each other. But in staggered conformation the hydrogen atoms are at maximum possible distance, So it is more stable.

Write the possible conformations of ethane and explain which is more stable.

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