Ab initio vibrational analysis of cyclopropene, its fluoro derivatives, and their deutero analogues

Total geometry optimization and computation of the ab initio force fields for cyclopropene and six of its fluoro derivatives are carried out at the HF/6-311G* level. The HF/6-311G*//HF/6-311G* force field of cyclopropene is scaled using the empirical scale factors determined only from the experimental vibrational frequencies of the light isotopic species of cyclopropene. The scaled force field obtained is used to calculate the vibrational frequencies for seven deutero analogues of cyclopropene and six of its fluoro derivatives. The scale factors for the >CF2 moiety of 3,3-difluorocyclopropene are refined using the experimental vibrational frequencies of its light isotopic species. The refined set of scale factors is transferred to the HF/6-311G*//HF/6-311G* force field of 1,2,3,3-tetrafluorocyclopropene. The experimental vibrational frequencies of this molecule are used to refine the scale factors for the =C-F moieties. The scale factors obtained, together with the scale factors for cyclopropene, are used to predict the vibrational frequencies of the 3-fluoro-, 1,3,3-trifluoro-, 1-fluoro-, and 1,2-difluorocyclopropenes. The vibrational problems for all the molecules just mentioned and for some of their deutero analogues are solved using the HF/6-311G*//HF/6-311G* force fields corrected by the corresponding refined sets of scale factors. The complete assignments of all the fundamental frequencies are given. Some peculiarities of the vibrational spectra of this molecular series are discussed.