A microwave spectroscopic and quantum chemical study of propa-1,2-dienyl selenocyanate (H2CCHSeCN) and cyclopropyl selenocyanate (C3H5SeCN)

Abstract

The microwave spectra of propa-1,2-dienyl selenocyanate, H₂CCCHSeCN, and cyclopropyl selenocyanate, C₃H₅SeCN, are reported. The spectra of the ground and two vibrationally excited states of the ⁸⁰Se isotopologue and the spectrum of the ground state of the ⁷⁸Se isotopologue were assigned for one rotameric form of H₂CCCHSeCN. This conformer is characterized by a C–C–Se–C dihedral angle of 129(5)° from synperiplanar (0°) and is shown to be the global minimum of H₂CCCHSeCN. The spectra of the ground and of three vibrationally excited states of the ⁸⁰Se isotopologue, as well as of the ground state of the ⁷⁸Se isotopologue of one rotamer of C₃H₅SeCN were assigned. This conformer has a H–C–Se–C dihedral angle of 80(4)° from synperiplanar and is at least 3 kJ mol⁻¹ more stable than any other form of the molecule. The microwave study has been augmented by quantum chemical calculations at the B3LYP/6-311++G(3df,3pd) and MP2/6-311++G(3df,3pd) levels of theory.