intramolecular strain present due to nonbonded interactions between two eclipsed atoms or groups. It is, for example, one of the interactions responsible for the existence of a rotational barrier and hence restricted rotation about the C–C
bond in ethane. It has also been called Pitzer strain, torsional strain and bond opposition strain.
PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2206 (https://doi.org/10.1351/pac199668122193)