Torisonal vs. Steric Strain

[Thomas Hui 2J]

What is the difference between torsional and steric strain?

[Navi Sidhu 1F]

Torsional Strain: When rotating a molecule around a bond, the torsional strain is the repulsion caused by the electrons in between different groups when they pass by each other. Torsional strain can be lessened by rotating a molecule around a bond.

Steric Strain: Strain caused by the electrons in between different groups. Steric strain cannot be lessened by rotating the molecule around a bond.

[Stephanie Demo 2N]

Steric strain is the result of nonbonded interaction. On page 107 of the course reader you can see that the strain arises from hydrogens bonded to different carbons trying to occupy the same space. Torsional strain comes from electron repulsion when a molecule is rotating between staggered and eclipsed conformations.