Infrared and Raman Spectra, Theoretical Calculations, Conformations, and Two-Dimensional Potential Energy Surface of 2-Cyclopenten-1-one Ethylene Ketal

Abstract

The infrared and Raman spectra of the bicyclic spiro molecule 2-cyclopenten-1-one ethylene ketal (CEK) have been recorded. Density functional theory (DFT) calculations were used to compute the theoretical spectra, and these agree well with the experimental spectra. The structures and conformational energies for the two pairs of conformational minima, which can be defined in terms of ring-bending (x) and ring-twisting (τ) vibrational coordinates, have also been calculated. Utilizing the results from ab initio MP2/cc-PVTZ computations, a two-dimensional potential energy surface (PES) was calculated. The energy levels and wave functions for this PES were then calculated, and the characteristics of these were analyzed. At lower energies, all of the quantum states are doubly degenerate and correspond to either the lower-energy conformation L or to conformation H, which is 154 cm(-1) higher in energy. At energies above the barrier to interconversion of 264 cm(-1), the wave functions show that the quantum levels have significant probabilities for both conformations.

Vapor-phase infrared and Raman spectra and ab-initio calculations of the axial and equatorial forms of cyclohexane-d1 and d11

“…The density functional theory (DFT) B3LYP method [11,12] was used with the cc-pVTZ basis set. The scaling factor of 0.961 was used for the vibrations of interest, based on previous work [13][14][15][16][17][18], which also has shown us that B3LYP/cc-pVTZ calculations do a better job than MP2/cc-pVTZ for reproducing vibrational frequencies.…”

Vibrational Spectra, Theoretical Calculations, and Two-Dimensional Potential Energy Surface for the Ring-Puckering Vibrations of 2,4,7-Trioxa[3.3.0]octane

“…For SSH, the PES has the form of eq 1 but does not require the x 1 x 2 term. We recently also calculated the PES for two out-of-plane ring vibrations of 2-cyclopenten-1-one ethylene ketal 19 (CEK) and analyzed its energy levels and wave functions. The two-dimensional PES for CEK has two pairs of energy minima at two different conformational energies.…”