Conformational stability and vibrational assignment of propanal

Operando Spectroscopy of the Gas-Phase Aldol Condensation of Propanal over Solid Base Catalysts

“…propanal) (2972-2720 cm − 1 ) and to aromatic/ olefinic species (3058 cm − 1 ) are observed. In the carbonyl stretching region and immediately after starting reaction, the ν C=O of propanal emerges with a doublet at 1760 and 1734 cm − 1 , indicative of both gas phase and chemisorbed propanal, respectively [45]. With increasing time-on-stream both absorption bands increase till saturation levels (Fig.…”

“…Within the first minutes of reaction, bands in the range 2963-2718 cm − 1 emerge and are ascribed to aliphatic C-H stretching (ν C−H ) vibrations. Although the assignment of these bands is not straightforward, the band at 2718 cm − 1 can be unambiguously assigned to a Fermi resonance structure of the CH stretching vibrations from aldehydes [43,45,46]. After two minutes of reaction, a ν C−H band arises at 3047 cm − 1 , most likely originating from aromatic species [43].…”

Millimeter and submillimeter wave spectroscopy of propanal

“…However, its energy of 219.9 cm −1 [4,5] is not only comparable to 24 = 2 at 269.3 cm −1 , the second excited state of the aldehyde torsion (A ), but also to the A CCC-bending fundamental 15 = 1 at 264.0 cm −1 [4,5]. Thus, Coriolis interaction may occur between 23 = 1 and 15 = 1.…”

“…2. The torsional potentials were determined more accurately by Far-IR spectroscopy [4] and higher-lying vibrational modes were studied by Mid-IR spectroscopy [5]. In particular, the first aldehyde torsion 24 = 1 is 135.1 cm −1 and the first excited methyl torsion 23 = 1 is 219.9 cm −1 above the ground state of syn [4]; note that the methyl torsional assignments have been exchanged between syn and gauche from Ref.…”

“…[4] to Ref. [5]. In the former work the energy difference between the conformers was redetermined as Figure 1: Sketch of syn propanal, CH 3 CH 2 CHO.…”