Question

Torsional strain in eclipsed conformations of a molecule is due to:

• A. Repulsion between the eclipsed carbons
• B. Repulsion between aligned electron pairs of the eclipsed bond
• C. Repulsions between aligned 'H'
• D. None of the above

Answer 1

The correct option is B Repulsion between aligned electron pairs of the eclipsed bond

Tortional strain is caused by repulsion of the bonding electrons of one substituent with bonding electrons of a nearby substituent.
In eclipsed conformers the substituents attached on adjacent carbon are at the minimum distance. Thus, the eclipsed bonds are parallel to each other, facing repulsions due to aligned electron pairs in the bonds.