Browsing by Author "Guillemin, Jean-Claude"

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Conformational analysis of ethyl-substituted Criegee intermediate by FTMW spectroscopy
(2016-12-14)
Cabezas, Carlos
;
Guillemin, Jean-Claude
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Ethyl-substituted Criegee intermediate, C2H5CHOO, has been generated in the discharged plasma of a 1,1-diiodopropane/O-2 gas mixture and spectroscopically characterized by Fourier transform microwave spectroscopy in a pulsed supersonic jet. The comparison between the experimental rotational constants and those calculated ab initio unambiguously confirms the identification of three conformers, providing the definitive probe for their molecular structures. Some of the observed pure rotational transitions show small splittings corresponding to the A/E components due to the threefold methyl internal rotation, which made it possible to determine the barrier heights of the hindered methyl rotation. The conformational abundances as well as the non observation of a plausible fourth conformer have been rationalized in terms of interconversion processes between conformers and interactions between the terminal oxygen and the protons of the ethyl moiety. Published by AIP Publishing.
Conformational preferences of Criegee intermediates: Isopropyl substituted carbonyl oxide
(2018-08-28)
Cabezas, Carlos
;
Guillemin, Jean-Claude
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Three conformers of the isopropyl-substituted Criegee intermediate, (CH3)(2) CHCHOO, have been observed by Fourier transform microwave spectroscopy. The transient species was produced using a pulsed electric discharge of a gas mixture of 1,1-diiodo-2-methylpropane/O-2 diluted in Ar or Ne. The use of different carrier gases in the supersonic expansion reveals the difference of the collisional relaxation process between anti-conformers. The conformational relaxation pathways have been investigated theoretically and are presented as well. In light of these results, the previous study on the ethyl-substituted Criegee intermediate, where the absence of one of the four possible conformers was associated with collisional relaxation processes, has been re-examined. Here we report the detection of a new conformer of the ethyl-substituted Criegee intermediate observed using Ne as the seeding gas. Published by AIP Publishing.
Fourier transform microwave spectroscopy of Criegee intermediates: The conformational behaviour of butyraldehyde oxide
(2019-03-14)
Cabezas, Carlos
;
Guillemin, Jean-Claude
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Four conformers of the n-propyl-substituted Criegee intermediate, CH3CH2CH2CHOO, also named n-butyraldehyde oxide, have been observed by Fourier transform microwave spectroscopy. The transient species was produced using a pulsed electric discharge of a gas mixture of 1,1-diiodobutane/O-2 diluted in Ar or Ne. The observation of only syn species is in contrast to the results of other previous studies of alkyl-substituted Criegee intermediates, in particular, those for the structural isomers, isobutyraldehyde oxide ((CH3)(2)CHCHOO), and methyl-ethyl-ketone oxide (C2H5C(CH3)OO), for which syn and anti species have been observed coexisting in the gas phase.
Fourier-transform microwave spectroscopy of a halogen substituted Criegee intermediate ClCHOO
(2016-11-14)
Cabezas, Carlos
;
Guillemin, Jean-Claude
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Pure rotational spectra of the chloro-substituted Criegee intermediate (ClCHOO) were observed by Fourier-transform microwave spectroscopy. Two conformers (syn and anti) of the isolated molecule were identified from the rotational spectra of the parent and Cl-37 and C-13 isotopologues detected in natural abundance. Rotational constants, centrifugal distortion constants, and all components of the nuclear quadrupole coupling tensor were determined for both conformers. Structural features of the molecule have been rationalized with supporting ab initio calculations and the natural bond orbital analysis, which suggest that the conformational preferences are driven by hyperconjugative effects. Published by AIP Publishing.
Probing the conformational behavior of the doubly substituted methyl-ethyl Criegee intermediate by FTMW spectroscopy
(2017-05-07)
Cabezas, Carlos
;
Guillemin, Jean-Claude
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Four conformers of the doubly substituted methyl-ethyl Criegee intermediate, C2H5C(CH3) OO, have been observed by Fourier-transform microwave spectroscopy. The transient species was produced using a pulsed electric discharge of a gas mixture of 2,2-diiodobutane/O-2. The conformational preferences differ from those observed previously for related alkyl-substituted Criegee intermediates. The observation of small splittings in the spectra due to the internal rotation of only one methyl group enabled us to determine the barrier heights of the hindered methyl rotation for the four conformers, which have been compared with those reported for other methyl-substituted Criegee intermediates. Published by AIP Publishing.