Under Pressure: Two Types of Strain That Molecules Can Experience

Molecules encounter strain when their chemical structure experiences some stress which leads to an increase in its internal energy. A strained molecule therefore has a greater amount of internal energy than an unstrained molecule, and only the bonds holding the molecule together prevent the release of this potential energy. Two types of strain are steric strain and torsional strain. Steric strain (also known as Van der Waals strain) occurs when atoms are forced closer together than is allowed by their Van der Waals radii allow. The size of the groups that interact determines the amount of steric strain on the molecule. Torsional strain is dependent on conformation, and occurs when atoms that are separated by three bonds are put in an eclipsed conformation instead of a staggered conformation. This brings the atoms into close proximity and increases their potential energy, which makes the conformation unstable. Torsional strain can resist bond rotation.