Comparative study of structure and photo-induced reactivity of malonaldehyde and acetylacetone isolated in nitrogen matrices

Abstract

Structure and reactivity of the eight enolic forms (one chelated and seven non-chelated) of malonaldehyde and acetylacetone are compared through theoretical and experimental data. Ground-state geometries, energies, and vibrational frequencies are calculated with the B3LYP/6-311++G(2d,2p) model chemistry. The electronic delocalisation as well as the cis/trans rotamer properties are analysed. The hydrogen bond strength of the chelated forms can be estimated by the energy difference between chelated and non-chelated forms, and its enhancement due to methyl-induced electron release is estimated at 1.7 kcal·mol -1 . UV-and IR-induced reactivity of molecules isolated in nitrogen matrices is studied by means of FT-IR spectrometry. Interconversion between rotamers is the main process observed for both molecules, only some among the seven non-chelated forms being created.PACS: 36.20.Ng, 31.15.Ar

Double deuterated acetylacetone in neon matrices: infrared spectroscopy, photoreactivity and the tunneling process

“…17 Many experimental and theoretical works support the Cs symmetry. 10,11,21 They are obtained by rotations around three bonds, two CC bonds and one CO bond as shown in Fig. 1 -and seven open conformers * .…”

Nuclear Spin Conversion to Probe the Methyl Rotation Effect on Hydrogen‐Bond and Vibrational Dynamics

“…Alternatively, the H int tunneling process could be quenched by coupling with phonon in the matrix environment. Such process was observed for MA in inert gas matrices24, 25 and Ar clusters,21 but it is unlikely in the present soft parahydrogen environment: as H int transfer is coupled with methyl torsions, this quenching should also affect “A”–“E” tunnelling splitting and it is obviously only a weak effect in solid p‐H 2 . Hacac spectra in solid neon (Figure 2 c) and solid xenon17 are very similar to the ms spectrum (Figure 3).…”

Selective photoisomerisation of 2-chloromalonaldehyde

“…In matrices, the UV-induced interconversions between enol conformers of MA, including back conversion to CCC, were clearly observed by detecting the photoproduced conformers. 24,[26][27][28][29] Four open enol conformers of MA produced by UV irradiation were identified, namely, CTC, TTC, TCT, and TTT conformers in rare gas matrices 24 and TCC, TTC, TCT, and TTT conformers in nitrogen matrices. 28 In the case of 2-ClMA, only three open enol conformers (CTC, TTC, and TCT) were obtained in Ar, Ne, and pH 2 .…”

“…Some of the MA open conformers have been observed in different cryogenic matrices, following UV irradiation of the samples. 24,26,28,29 UV photoisomerization in matrices was also extensively studied in the case of the closely related molecule: acetylacetone (AcAc). [30][31][32][33][34] AcAc is the simplest β-diketone obtained by exchanging the hydrogen atoms linked to carbons 1 and 3 in MA (see Fig.…”

“…Because of steric effects, the relative energy of TTZ conformers compared to the chelated enol (CCC) is much higher in AcAc than in MA and the observation of these conformers is difficult. 28 Moreover, a strong matrix effect was observed in the case of AcAc on the photoisomerization process with the production of different conformers depending on the matrix host. 31,33,34 The present study based on the UV isomerization of 2-ClMA in matrices aims at the characterization of its nonchelated conformers and of the isomerization process.…”