Ab Initio Vibrational Analysis of Cyclopropene, Its Fluoro Derivatives, and Their Deutero Analogues

Abstract

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.

Structure, Synthesis, and Chemical Reactions of Fluorinated Cyclopropanes and Cyclopropenes

“…207 Additional structural data was obtained by single-crystal X-ray diffraction at 156 K of C 3 F 4 (mp 196-199 K), which was in good agreement with the gas phase and NMR results. Complementary to these experimental results (see Table 3), various ab initio calculations 207,208 have provided reasonably accurate information on essentially all of the fluorinated cyclopropenes, including the as yet unknown 1,2-difluoro-and 1-fluorocyclopropene. 209 As seen in Table 3, fluorine substitution at the methylene carbon of cyclopropene results in significant lengthening of the CdC bond and shortening of the C-C single bonds, analogous to similar effects seen in the cyclopropane system (see Table 1).…”

New perspectives in the PAW/GIPAW approach: JP-O-Si coupling constants, antisymmetric parts of shift tensors and NQR predictions

“…H-relaxed structure was used only in the case of α-NTO. Cyclopropene and tetrafluorocycloprene theoretical geometries were used, [41] and atomic positions were additionally relaxed using DFT calculations. For tetrachlorocycloprene, the initial geometry of tetrafluorocycloprene was used with C-Cl distances modified to fit with known values.…”

Isolable Copper(I) η2-Cyclopropene Complexes

“…Interestingly, the carbonyl group of the CO 2 Et moiety also coordinates to copper, albeit weakly as evident from the relatively long Cu–O bond distances (2.2625(10)–2.2983(7) Å) compared with typical Cu–O­(ester) separations of ∼2.00 Å (Table S2) as well as 1.954 Å of [(CF 3 ) 2 Tp]­Cu­(Cyp- 2 ) noted below, and nearly trigonal planar copper sites with the sum of angles (excluding oxygen) at copper of ∼354–356° compared to 360° and 328° for ideal trigonal planar and tetrahedron arrangements, respectively. The copper-bound CC distances (1.3481(12), 1.3583(18), and 1.3659(11) Å) display a significant lengthening relative to typical CC distances of free cyclopropenes (e.g., 1.296 Å for parent cyclopropene and 1.2968(12) Å for Cyp- 3 (see Supporting Information for the crystal structure)). The olefinic carbon centers of copper coordinated cyclopropene ligands in [(CF 3 ) 2 Bp]­Cu­(Cyp- 2 ), [(CF 3 ) 2 Bp]­Cu­(Cyp- 3 ), and [(CF 3 ) 2 Bp]­Cu­(Cyp- 4 ) show clear pyramidalizations with the sum of the angles of 340–343° at olefinic carbons (not involving copper).…”