Question

What is torsional strain?

Answer 1

Hint: In chemistry, strain occurs when a molecule's chemical structure is stressed, raising its internal energy in comparison to a strain-free reference substance. All of the energy held within a molecule makes up the molecule's internal energy. An unstrained molecule does not have any internal energy, but a strained molecule has. This additional internal energy, also known as strain energy, may be compared to a compressed spring.

Complete answer:
When atoms are forced to move closer than their Van der Waals radii allow, Van der Waals strain, also known as steric strain, develops. Van der Waals strain is defined as a type of strain in which the interacting atoms are separated by at least four bonds. The degree of steric strain in comparable molecules is determined by the size of the interacting groups; bulky tert-butyl groups take up considerably more space than methyl groups, and so have more steric interactions. Nobel laureate Herbert C. Brown et al. investigated the effects of steric strain in the reaction of trialkyl amines with trimethylboron.
They discovered that as the size of the alkyl groups on the amine grew larger, so did the equilibrium constant. The steric tension between the alkyl groups of the amine and the methyl groups on boron was blamed for the shift in equilibrium. The strain faced by the bonds is defined as torsional strain, which occurs when conformations are not staggered. Torsion pressure exists at any angle other than 60, 120, or 180 degrees. Furthermore, torsional strain can only arise when atoms are separated by just three bonds.

Note:
The main difference between steric and torsional strain is that steric strain cannot be decreased by spinning the molecule around a bond, but torsional strain may be reduced by rotating the molecule around a bond.