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Article Dans Une Revue Journal of Physical Chemistry A Année : 2021

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

Alejandro Gutiérrez-Quintanilla
Rasa Platakyte
  • Fonction : Auteur
Michèle Chevalier
  • Fonction : Auteur
Justinas Ceponkus
  • Fonction : Auteur

Résumé

Enol forms of trifluoroacetylacetone (TFacac) isolated in molecular and rare gas matrices were studied using infrared (IR) and Raman spectroscopy. Additionally, calculations using DFT B3LYP and M06-2X as well as MP2 methods were performed in order to investigate the possibility of coexistence of more than one stable enol form isomer of TFacac. Calculations predict that both stable enol isomers of TFacac, 1,1,1-trifluoro-4-hydroxy-3-penten-2-one (1) and 5,5,5-trifluoro-4-hydroxy-3-penten-2-one (2), could coexist, especially in matrices where the room temperature population is frozen, 1 being the most stable one. Raman and IR spectra of TFacac isolated in nitrogen (N2) and carbon monoxide (CO) matrices exhibit clear absorption bands, which cannot be attributed to this single isomer. Their relative band positions and intensity profiles match well with the theoretical calculations of 2. This allows us to confirm that in N2 and CO matrices both isomers exist in similar amounts. Careful examination of the spectra of TFacac in argon, xenon, neon, normal, and para-hydrogen (Ar, Xe, Ne, nH2, and pH2 respectively) matrices revealed that both isomers coexist in all the explored matrices, whereas 2 was not considered in the previous spectroscopic works. The amount of the second isomer (2) in the as-deposited samples depends on the host. The analysis of TFacac spectra in the different hosts and under various experimental conditions allows the vibrational characterization of both chelated isomers. The comparison with theoretical predictions is also investigated.
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Dates et versions

hal-03189914 , version 1 (10-08-2021)

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Alejandro Gutiérrez-Quintanilla, Rasa Platakyte, Michèle Chevalier, Claudine Crépin, Justinas Ceponkus. Hidden Isomer of Trifluoroacetylacetone Revealed by Matrix Isolation Infrared and Raman Spectroscopy. Journal of Physical Chemistry A, 2021, 125 (11), pp.2249-2266. ⟨10.1021/acs.jpca.0c10945⟩. ⟨hal-03189914⟩
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