Vibrational Anharmonicities and Reactivity of Tetrafluoroethylene

Abstract

Compared to ethylene and its nonfluorinated derivatives, C2F4 is peculiar in many reactions. It very easily adds to radicals and prefers formation of four-membered rings over Diels–Alder reactions. This has been rationalized by the preference of fluorine for carbon sp3 hybridization, which is possible on opening of the double bond. Another property, the thermal dissociation of the C=C bond, has been explained by the stabilization of the product (CF2) by back-bonding. Here, it is attempted to correlate such properties with vibrational constants, in particular for C=C stretching and twisting and for carbon pyramidalization. The only force constant found to be lowered compared to ethylene is that for trans pyramidalization (ν8), and CC bond softening on ν8 distortion is indicated by the conspicuously large magnitude of anharmonic constant, x18. Both observations can be rationalized by a valence-bond model that predicts a trans bent structure on weakening the CC bond. Conclusions are drawn about the dissociation path and peculiarities of the potential. Other anharmonicities, both experimental and calculated and some in 12C13CF4 and 13C2F4, are also discussed. In particular some strong Fermi resonances are identified and their effects accounted for.

The Limits of Rovibrational Analysis: The Severely Entangled ν1 Polyad Vibration of Dichlorodifluoromethane in the Greenhouse IR Window

“…This is generally an indicator of Fermi resonance, and the largest effects occur when isotopic substitution causes interacting levels to switch their energy ordering, as was recently observed and elaborated for the ν 5 CF stretch mode of C 2 F 4 . 33,34 This is particularly evident for ν 6 , in Fermi resonance with ν 3 + ν 7 . In the 12 C species, ν 6 is elevated by the resonance as ν 3 + ν 7 lies lower in energy, 20 but in the 13 C species, the lower wavenumber band at 876 cm −1 is more intense and so is assigned to ν 6 rather than its accompanying (ν 3 + ν 7 ) band at ≈905 cm −1 .…”

The 235–360 GHz Rotational Spectrum of 1-Oxaspiro[2.5]octa-4,7-dien-6-one─Analysis of the Ground Vibrational State and Its 10 Lowest-Energy Vibrationally Excited States

“… a Anharmonic frequencies calculated at the B3LYP/6-311+G(2d,p) level. Overtones 3ν 22 , 4ν 22 , and 5ν 22 estimated from the anharmonicity constant …”

“… a Anharmonic frequencies calculated at the B3LYP/6-311+G­(2d,p) level. Overtones 3ν 22 , 4ν 22 , and 5ν 22 estimated from the anharmonicity constant b Bracketed values held constant at their respective ground-state value or a value extrapolated from lower-energy vibrational states using an appropriate polynomial. c Number of independent transition frequencies. d κ = (2 B – A – C )/( A – C ), using PLANM. e Inertial defect (Δ i = I c – I a – I b ) calculated from the B v constants using PLANM. …”

“…The resulting energy values are presented in Table , along with their B3LYP/6-311+G(2d,p) and MP2/6-311+G(2d,p) computed values. The computed values of the higher-energy overtone states that are not calculated by the Gaussian routine were determined using eq , where ν is the fundamental frequency, v 22 is the vibrational quantum number, and x ii is the anharmonicity constant, in the manner described by Fuß et al E v 22 − E 0 = v 22 ν + v 22 x 22 , 22 false( normalv 22 − 1 false) …”

The Spectroscopic Characterization of Halogenated Pollutants through the Interplay between Theory and Experiment: Application to R1122

“…Within this framework, several investigations (see, for example, refs. [ 23 , 24 , 25 , 26 , 27 , 28 , 29 ] and references therein) have been carried out to disentagle the anharmonic interactions in their vibrational spectra and to assess the quality of the predicted dipole moment surfaces against the spectroscopic experimental data.…”