Vibrational spectra, conformational properties and argon matrix photochemistry of diacetyl diselenide, CH₃C(O)Se₂C(O)CH₃

Abstract

By oxidation of selenoacetic acid, CH3C(O)SeH, we have prepared the hitherto unknown diacetyl diselenide, [CH3C(O)Se]2. Its vibrational properties were studied experimentally, both in neat liquid (Fourier transform infrared spectroscopy and Raman) with the molecule isolated in argon matrix at low temperatures and theoretically using MP2 and B3LYP methods in combination with 6‐31+G(d), 6‐311++G(3df,3dp) or aug‐cc‐pvDZ basis sets. Analysis of Ar matrix spectra reveals a conformational equilibrium in gas phase at room temperature, which was interpreted by considering only two of the three stable rotamers predicted by our three‐dimensional potential energy surface scans. Energetic properties of three minima found theoretically were further studied in terms of donor–acceptor interactions by using natural bond orbital calculations at the same levels of theory. From this, it was possible to rationalize the conformational stability order and molecular structures by means of vicinal hyperconjugative delocalizations involving lone pairs on selenium or oxygen atoms and C=O, C–C or Se–C antibonding orbitals. The photochemistry of the compound in the argon matrix in the range between 200 and 800 nm was also investigated, revealing only one photochemical path to produce ketene, H2C=C=O, methylselane, CH3SeH, and carbonyl selenide, OCSe. Copyright © 2016 John Wiley & Sons, Ltd.

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“…The most distinctive signals of selenium can be found in the low wavenumber region of 400-600 cm −1 , with weak peaks at 580, 520, and 436 cm −1 (Figure 2b inset).The strong band at 436 cm −1 could be assigned to the torsional vibrations of the hexagonal rings, coupled with the out-ofplane γ(C-Se) bending vibrations [27]. The peaks at 580 and 520 cm −1 correspond to C-Se bending vibrations [28,29]. Clearly, these peaks verify the existence of C-Se bonds in the c-PAN-Se.…”