Torsional barrier height of thionitrous acid is analysed with Gaussian-2(G2), quadratic complete basis set (CBS-Q) and DFT-B3LYP/CBS-Q (CBS-QB3) methods. In agreement with purely intuitive arguments, it was determined that the cis to trans barrier height is nearly 5.7–6.3 kcal mol − 1. In addition, the stability of rotation as function of competing dissociation pathways and also result of natural bond orbital analysis are discussed.
