UV Photochemistry of Acetylacetaldehyde Trapped in Cryogenic Matrices

Abstract

The broad band UV photochemistry of acetylacetaldehyde, the hybrid form between malonaldehyde and acetylacetone (the two other most simple molecules exhibiting an intramolecular proton transfer), trapped in four cryogenic matrices, neon, nitrogen, argon, and xenon, has been studied by IRTF spectroscopy. These experimental results have been supported by B3LYP/6-311G++(2d,2p) calculations in order to get S 0 minima together with their harmonic frequencies. On those minima, we have also calculated their vibrationally resolved UV absorption spectra at the time-dependent DFT ωB97XD/6-311+ +G(2d,2p) level. After deposition, only the two chelated forms are observed while they isomerize upon UV irradiation toward nonchelated species. From UV irradiation effects we have identified several nonchelated isomers, capable, in turn, of isomerizing and fragmenting, even if this last phenomenon seems to be most unlikely due to cryogenic cages confinement. On the basis of these findings, we have attempted a first approach to the reaction path of electronic relaxation. It appeared that, as with acetylacetone, the path of electronic relaxation seems to involve triplet states.Article pubs.acs.org/JPCA

UV photoreaction pathways of acetylacetaldehyde trapped in cryogenic matrices

“…From the first five seconds of irradiation, the other bands in the argon and nitrogen spectra are observed at -41.5, -49 and -50.5 nm, and -43.5 and -46.5 nm, respectively. Based on the vibrational assignments made in the previous paper, 1 and by comparing the shifts in the UV absorption bands, in argon and nitrogen, with the theoretical results, we can reasonably assume that all the nonchelated isomers are formed and observed except for CCT. However, can we make a reliable electronic attribution of the UV spectra?…”

“…Acetylacetaldehyde [1][2][3][4][5] (hereafter referred as AAD) is one of the most simple molecule, together with malonaldehyde 6 (hereafter referred as MA) and acetylacetone ? ?…”

Hidden Isomer of Trifluoroacetylacetone Revealed by Matrix Isolation Infrared and Raman Spectroscopy

“…1,2 The smallest members of these molecular families are malonaldehyde and acetylacetone (acac), with symmetric substituents linked to the pseudo ring and widely investigated in previous matrix works, [3][4][5][6][7][8] and the asymmetric acetylacetaldehyde. 9 This type of molecules can exist in two tautomeric forms, namely enol and keto, the enol form being the most stable one due to the strong internal hydrogen bond. 7 These molecules in enolic configuration possess double well potential function for the proton transfer from one oxygen to the other (Figure 1a).…”

“…The molecules possessing a pseudo ring structure where a hydrogen bond “closes” this ring form a peculiar class of molecules where properties of the hydrogen bond (H-bond) are strongly dependent on the delocalized π type electronic structure of the molecule. Such type of hydrogen bonding is often called resonance-assisted hydrogen bonding (RAHB). , The smallest members of these molecular families are malonaldehyde and acetylacetone (acac), with symmetric substituents linked to the pseudo ring and widely investigated in previous matrix works, − and the asymmetric acetylacetaldehyde . This type of molecules can exist in two tautomeric forms, namely, enol and keto, the enol form being the most stable one due to the strong internal hydrogen bond .…”