B3LYP/6-311++G(3df, 3pd) potential curve for the rotation about the C3-N4 bond. The abscissa is the H5-N4-C3-H11 dihedral angle. Conformer I has the lowest energy indicated by 0 kJ/mol for dihedral angle of 59.4°. Rotamer II is higher in energy by 8.5, and III by 7.5 kJ/mol relative to I. The corresponding dihedral angles are 179.9 and 320°, respectively. The maxima have higher energies than I by 14.1, 15.3, and 12.4 kJ/mol, respectively. The corresponding dihedral angles are 128.8, 236, and 348.9°, respectively.