Question

Write 2 conformers of ethane and tell which is more stable

Answer 1

✔️There are two conformations of ethane:-

⭕️Staggered conformation.

⭕️Eclipsed conformation.

✔️staggred conformation of ethane is more stable than eclipse conformation.

As:-

⏹In staggered conformation hydrogen atoms on one carbon atom lie inbetween hydrogen atoms bonded to the second carbon atom.

⏹In eclipsed form the hydrogen atoms of two carbon atoms lie adjacent to each other.

⏹In staggered conformation the dihedral angle is 60o which is the maximum distance between two H-atoms and so there is no repulsion between bond pair electrons.

⏹in eclipsed conformation the dihedral angle is 0o 

⏹H-atoms are lined perfectly behind one another which causes repulsion between bond pairs of H-atoms.

⭕️Hence, staggred conformation of ethane is more stable than eclipse conformation.

Answer 2

Two conformations of ethane are:

A. Staggered conformation.
B. Eclipsed conformation.

1.The lowest energy conformation of ethane, shown in the figure above,  is called the ‘staggered’ conformation.

=>all of the C-H bonds on the front carbon are positioned at dihedral angles of 60°relative to the C-H bonds on the back carbon.
=>distance between the bonds (and the electrons in them) is maximized.

2. If we now rotate the front CH3 group 60°clockwise, the molecule is in the highest energy ‘eclipsed' conformation, where the hydrogens on the front carbon are as close as possible to the hydrogens on the back carbon.

=>This is the highest energy conformation because of unfavorable interactions between the electrons in the front and back C-H bonds.  

=>The energy of the eclipsed conformation is approximately 3 kcal/mol higher than that of the staggered conformation.

 ***The most stable (low energy) conformation is the one in which all six C–H bonds are as far away from each other as possible (staggered).  The least stable (high energy) conformation is the one in which the six carbon–hydrogen bonds are as close as possible (eclipsed).