Conformational structures and energies, rotational barrier heights and torsional oscillations in tetrahalodiphosphines, tetrahalohydrazines and X2NPX2 molecules

Using molecular-mechanics calculations and gas-phase atom—atom interaction potentials, the torsional potentials of tetrahalodiphosphines, tetrahaloghydrazines and X2NPX2 molecules were calculated. All these molecules have low-energy anti conformations. For Cl2PPCl2 and X2NNX2 (XCl, Br or I) gauche is also a low-energy conformation. For the anti forms the following wavenumbers (cm−1) of the torsional oscillations were obtained by normal-coordinate analysis (X  Cl, Br or I): X2PPX2 35–50, X2NPX2 45–80 and X2NNX2 60–120.