Molecular structure and vibrational spectra of 2(5H)-furanone and 2(5H)-thiophenone isolated in low temperature inert matrix

Abstract

The structure and vibrational spectra of two five-membered heterocyclic a-carbonyl compounds have been studied. The experimental FTIR spectra 2(5H)-furanone and 2(5H)-thiophenone monomers isolated in inert argon matrices at 10 K are reported and discussed. The interpretation of the experimental data is supported by vibrational calculations at the MP2 and DFT(B3LYP) levels of theory with the 6-311++G(d,p) basis set. Spectra/structure correlations were extracted from the data calculated for the two title compounds and for their six-membered ring analogues, a-pyrone and thiapyran-2-one. The vibrational frequencies of the C@O, CC, CH and CH 2 moieties were correlated with the ring size, atomic charges and the nature of heteroatom. Natural bond orbital analysis revealed important details of the electronic structure and dominant intramolecular interactions in 2(5H)-furanone and 2(5H)-thiophenone and provided an additional insight into their vibrational spectra.

UV-induced unimolecular photochemistry of 2(5H)-furanone and 2(5H)-thiophenone isolated in low temperature inert matrices

“…The theoretical calculations predict that if the carbonyl group is attached to a saturated hydrocarbon ring of varying size, then the carbonyl stretching frequency will increase with the decrease of the ring [35]. Interestingly, this general rule holds also for the conjugated heterocyclic rings, and the nC O) vibration for the carbonyl group attached to a 6-membered (thiopyranone), 5-membered (thiophenone) and 4-membered (TD analogues) ring is observed at 1672.5 [36], 1713.9 [1] and 1777.5 cm À1 (present work), respectively. The presence of carbonyl sulphide and of the Dewar isomer is confirmed by the observation of other bands fitting well the calculated spectra of OCS and TD in the fingerprint region ( Fig.…”

“…The experimental apparatus and procedures are described elsewhere [1]. The chosen compound was placed in a glass ampoule protected against light and connected to the sample chamber of an APD Cryogenics DE-202A closed-cycle helium cryostat through a NUPRO SS-4BMRG needle valve with shut-off possibility.…”

“…The infrared spectrum of 2(5H)-thiophenone (or, for brevity, thiophenone) monomers isolated in argon matrix was reported in our previous study [1]. The experimental data were compared with Scheme 1.…”

“…Recently, the structure and vibrational spectra of two fivemembered heterocyclic a-carbonyl compounds, 2(5H)-thiophenone and 2(5H)-furanone (Scheme 1), have been studied in our laboratory [1]. The experimental FTIR spectra of the monomers of these compounds isolated in inert argon matrices at 10 K were investigated, the interpretation of the experimental data being supported by vibrational calculations at the MP2 and DFT(B3LYP)/ 6-311++G(d,p) levels of theory.…”

“…However they would require the simultaneous occurrence of an intramolecular [1,2]hydrogen shift (Scheme 3). This requirement could be expected to introduce important differences in the reactivity of the two types of compounds.…”