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Title: Structural, spectroscopic, and photochemical study of ethyl propiolate isolated in cryogenic argon and nitrogen matrices
Authors: Lopes, S. 
Nikitin, Timur 
Rui Fausto 
Keywords: Conformational analysis; Ethyl propiolate; Matrix isolation infrared spectroscopy; Photochemistry
Issue Date: 5-Nov-2020
Publisher: Elsevier
Project: info:eu-repo/grantAgreement/FCT/SFRH/BPD/77276/2011 
Serial title, monograph or event: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy
Volume: 241
Abstract: Ethyl propiolate (HC ≡ CCOOCH2CH3, EP) was studied experimentally by infrared spectroscopy in argon and nitrogen cryomatrices (15 K) and by quantum chemical calculations (at the DFT(B3LYP) and MP2 levels of theory). Calculations predict the existence of four conformers: two low-energy conformers (I and II) possessing the carboxylic moiety in the cis configuration (O=C-O-C dihedral equal to ~0°) and two higher-energy trans forms (O=C-O-C dihedral equal to ~180°; III and IV). The conformation of the ethyl ester group within each pair of conformers is either anti (C-O-C-C equal to 180°; in conformers I and III) or gauche (C-O-C-C equal to ±86.6° in II, and ± 92.5° in IV). The two low-energy cis conformers (I and II) were predicted to differ in energy by less than 2.5 kJ mol-1 and were shown to be present in the studied cryogenic matrices. Characteristic bands for each one of these conformers were identified in the infrared spectra of the matrix-isolated compound and assigned taking into account the results of normal coordinate analysis, which used the geometries and harmonic force constants obtained in the DFT calculations. The two trans conformers (III and IV) were estimated to be 17.5 kJ mol-1 higher in energy than the conformational ground state (form I) and were not observed experimentally. The unimolecular photochemistry of matrix-isolated EP (in N2 matrix) was also investigated. In situ irradiation with UV light (λ > 235 nm) leads mainly to decarbonylation of the compound, with generation of ethoxyethyne, which in a subsequent photoreaction generates ketene (plus ethene).
ISSN: 13861425
DOI: 10.1016/j.saa.2020.118670
Rights: embargoedAccess
Appears in Collections:I&D CQC - Artigos em Revistas Internacionais

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