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

Lozada‐Garcia, Rolando Rafael; Čeponkus, Justinas; Chevalier, Michèle; Chin, W.; Mestdagh, J. M.; Crépin, C.

doi:10.1002/ange.201200727

Cited by 4 publications

(3 citation statements)

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“…The IR spectrum of CCC in pH 2 will be discussed in a forthcoming paper dedicated to this specific structure. 18 IR spectra recorded after UV irradiation at 266 nm exhibit many new narrow lines (bandwidths o2 cm À1 ) as shown in Fig. 2.…”

Section: Spectroscopymentioning

confidence: 95%

“…In particular, the CCC isomer presents broad bands, hiding a complex structure. 18 Its time evolution has thus been deduced by measuring the intensity of CCC in the whole spectrum at all time intervals. Bands of open isomers are narrower and direct measurement of their time evolution is performed on different bands of each isomer.…”

Section: Relaxation Process V1 Kinetic Studymentioning

confidence: 99%

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Photochemistry of acetylacetone isolated in parahydrogen matrices upon 266 nm irradiation

Lozada‐Garcia

Čeponkus

Chevalier

et al. 2012

Phys. Chem. Chem. Phys.

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The photochemistry of the chelated enol form of acetylacetone (AcAc) was investigated by UV excitation of the S(2) state at 266 nm in parahydrogen matrices, complemented by experiments in neon and normal hydrogen matrices. Infrared (IR) spectroscopy, combined with theoretical calculations, was used to identify the photoproducts. Isomerization towards various non-chelated forms (no intramolecular H-bond) of AcAc is the dominant channel whereas fragmentation is very minor. The isomerization kinetics is monitored by IR spectroscopy. Among the seven non-chelated conformers of AcAc, only three are formed in parahydrogen matrices, whereas four are observed in normal hydrogen matrices. This difference suggests that an active tunnelling process between conformers occurs in parahydrogen but is quenched in normal hydrogen where guest-host interactions are stronger. Fragmentation and isomerization of excited AcAc are discussed in the light of these new data. The role of the intermediate triplet state in the S(2)→ S(0) relaxation is confirmed, as the importance of phonons in the condensed phase.

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Section: Spectroscopymentioning

confidence: 95%

Section: Relaxation Process V1 Kinetic Studymentioning

confidence: 99%

Photochemistry of acetylacetone isolated in parahydrogen matrices upon 266 nm irradiation

Lozada‐Garcia

Čeponkus

Chevalier

et al. 2012

Phys. Chem. Chem. Phys.

Self Cite

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“…17 It should be noted that the controversy between the microwave, gas-phase electron diffraction, and quantum chemical calculation results for acetylacetone is attributed to the proton tunneling and low-barrier internal rotation of the two methyl groups making the microwave spectrum quite complex. [18][19][20][21][22][23] Based on the results obtained from the gas-phase electron diffraction and quantum chemical calculation analysis, the ground state structure of acetylacetone has C s symmetry. The origin of these differences from their higher symmetric forms (i.e., C 2v structure) is of significant interest.…”

Section: Introductionmentioning

confidence: 99%

Symmetry breaking in the axial symmetrical configurations of enolic propanedial, propanedithial, and propanediselenal: pseudo Jahn–Teller effect versus the resonance-assisted hydrogen bond theory

Jalali

Nori‐Shargh

2015

Can. J. Chem.

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The origin of the symmetry breaking in the axial symmetrical configurations of enolic propanedial (1), propanedithial (2), and propanediselenal (3) have been investigated by means of time-dependence density functional theory and natural bond orbital interpretations. The results obtained at the quantum chemistry composite (G2MP2, CBS-QB3), ab initio molecular orbital (MP2/6-311++G**), and hybrid density functional theory (B3LYP/6-311++G**) levels of theory showed that the hydrogen-centered synchronous axial symmetrical (C 2v ) configurations of compounds 1-3 possessing the maximum -electron delocalization within the M 1 =C 2 -C 3 =C 4 -M 5 -H 6 keto-enol groups are less stable than their corresponding plane symmetrical (C s ) forms. Importantly, the symmetry breaking in the C 2v configurations of the enol forms of compounds 1-3 to their corresponding plane symmetrical C s configurations is due to the pseudo Jahn-Teller effect (PJTE) by mixing the ground A 1 and excited B 2 electronic states resulting in a PJT (A 1 + B 2 ) R b 2 problem. We may expect that by the decrease of the energy gaps between reference states in the C 2v forms that are involved in the PJTE decrease from compound 1 to compound 3, the PJT stabilization energy (PJTSE) may increase but the results obtained showed that the corresponding PJTSEs decrease. This fact can be justified by the increase of the electron delocalizations from the nonbonding orbitals of the C=M moieties to the antibonding orbitals of the H-M bonds, which leads to an increase of the -electron delocalization within the M 1 =C 2 -C 3 =C 4 -M 5 -H 6 keto-enol groups. In confrontation between the impacts of the resonance-assisted hydrogen bond and PJTE in the structural and configurational properties of compounds 1-3, PJTE has an overwhelming contribution and causes the symmetry breaking of the C 2v configurations to their corresponding C s forms. The correlations between the structural parameters, synchronicity indices, natural charges, PJTSEs, electron delocalizations, and the hardness of compounds 1-3 have been investigated.Résumé : Nous avons étudié l'origine de la rupture de symétrie dans les configurations à symétrie axiale de la forme énolique du propanedial (1), du propanedithial (2) et du propanedisélenal (3) au moyen de la théorie de la fonctionnelle de la densité dépendant du temps et d'interprétations fondées sur l'orbitale liante naturelle. Les résultats obtenus à l'aide de la méthode composite de chimie quantique (G2MP2, CBS-QB3), de calculs ab initio des orbitales moléculaires (MP2/6-311++G**), des niveaux de calcul hybrides (B3LYP/6-311++G**) de la théorie de la fonctionnelle de la densité ont révélé que les configurations de symétrie axiale synchrones centrées sur les atomes d'hydrogène (C 2v ) des composés 1-3 qui possèdent la délocalisation maximale d'électrons à l'intérieur des groupements céto-énol M 1 =C 2 -C 3 =C 4 -M 5 -H 6 sont moins stables que les formes correspondantes de symétrie planaire (C s ). Fait important, la rupture de symétrie des configuration...

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Der Tunneleffekt von Atomen in der Chemie

Meisner

Kästner

2016

Angewandte Chemie

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Der quantenmechanische Tunneleffekt von Atomen wird immer häufiger als wichtiger Aspekt in chemischen Reaktionen identifiziert. Experimentell kann man Atomtunneln nur indirekt nachweisen; beispielsweise durch temperaturunabhängige Reaktionsgeschwindigkeitskonstanten oder durch sehr große kinetische Isotopeneffekte. Im Gegensatz dazu können theoretische Methoden den Einfluss des Tunneleffekts auf die Reaktionsgeschwindigkeit direkt bestimmen. Der Tunneleffekt ändert beispielsweise Reaktionspfade und Verzweigungsverhältnisse, ermöglicht chemische Reaktionen in astrochemischer Umgebung, die thermisch nicht stattfinden, und beeinflusst auch biochemische Prozesse.

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

Cited by 4 publications

References 25 publications

Photochemistry of acetylacetone isolated in parahydrogen matrices upon 266 nm irradiation

Photochemistry of acetylacetone isolated in parahydrogen matrices upon 266 nm irradiation

Symmetry breaking in the axial symmetrical configurations of enolic propanedial, propanedithial, and propanediselenal: pseudo Jahn–Teller effect versus the resonance-assisted hydrogen bond theory

Der Tunneleffekt von Atomen in der Chemie

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