Combined FTIR Matrix Isolation and Ab Initio Studies of Pyruvic Acid:  Proof for Existence of the Second Conformer

Reva, Igor; Stepanian, S. G.; Adamowicz, Ludwik; Fausto, Rui

doi:10.1021/jp0101458

Cited by 98 publications

(182 citation statements)

References 37 publications

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“…Due to its high hygroscopicity the compound was transferred from the factory packing into the effusive cell in a glove-box under dry nitrogen atmosphere. An effusive Knudsen cell 10 was equipped with a SS-4BMRG (NUPRO) needle valve with a shut-off possibility which prevented the sample coming into contact with the atmosphere before the experiments. Prior to the experiment, the cell was connected to the vacuum system of the cryostat and the compound was additionally purified from dissolved gases by pumping through the cryostat.…”

Section: Methodsmentioning

confidence: 99%

Stepwise conformational cooling towards a single isomeric state in the four internal rotors system 1,2-butanediol

Reva

Jesus

Rosado

et al. 2006

Phys. Chem. Chem. Phys.

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The present work explores the possibilities of the matrix isolation technique in the structural characterisation of highly flexible molecules. To date, most studies of this type were carried out on molecules with three or less internal degrees of freedom and a few (less than 10) possible conformations. The molecule of 1,2-butanediol has four conformationally relevant three-fold rotational axes, which can result in 81 possible conformations. A detailed theoretical study, at the MP2 and DFT(B3LYP) levels of theory with the 6-311++G(d,p) basis set, revealed that more than 20 conformers of 1,2-butanediol have relative energies in a 0-10 kJ mol À1 range and contribute appreciably to the gas phase equilibrium at room temperature. This fact renders conformational studies of the system extremely difficult under normal conditions. However, the method of matrix isolation permits the reduction of the number of populated conformational states in the experiment at low temperature due to the effect known as conformational cooling: low energy barriers promote the relaxation of the higher energy local minima into more stable structures. As a result of massive conformational cooling occurring upon matrix deposition, only five conformers of 1,2-butanediol were retained in the samples at 10 K. These conformers were identified using a combination of FTIR spectroscopy and extensive theoretical calculations of vibrational spectra. Annealing of the matrices up to 50 K resulted in the extreme case of conformational cooling related with the depopulation of all conformers into the most stable unique structure. The observed transformations were rationalized in terms of barriers to intramolecular rotation.

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Section: Methodsmentioning

confidence: 99%

Stepwise conformational cooling towards a single isomeric state in the four internal rotors system 1,2-butanediol

Reva

Jesus

Rosado

et al. 2006

Phys. Chem. Chem. Phys.

Self Cite

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show abstract

“…Due to their high hygroscopicity, they were transferred from the factory packing into the effusive cell in a glovebox previously purged with dry nitrogen. An effusive Knudsen cell 26 was equipped with a SS-4BMRG (NUPRO) needle valve and permitted to avoid the contact of the sample compartment with atmosphere before experiments. Prior to experiment, the cell was connected to the vacuum system of the cryostat, and the compound was additionally purified from dissolved gases by pumping.…”

Section: Methodsmentioning

confidence: 99%

Conformational Study of Monomeric 2,3-Butanediols by Matrix-Isolation Infrared Spectroscopy and DFT Calculations

et al. 2006

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The FT-IR spectra of two diastereomers of 2,3-butanediol, (R,S) and (S,S), isolated in low-temperature argon and xenon matrixes were studied, allowing the identification of two different conformers for each compound. These conformers were characterized by a (gauche arrangement around the O-C-C-O dihedral angle, thus enabling the establishment of a very weak intramolecular hydrogen bond of the O‚‚‚H-O type. No other forms of these compounds were identified in matrixes, despite the fact that these four conformers had calculated relative energies from 0 to 5.1 kJ mol -1 and were expected to be thermally populated from 50 to 6% in the gaseous phase of each compound. The nonobservation of additional conformers was explained in terms of low barriers to intramolecular rotation, resulting in the conformational relaxation of the compounds during deposition of the matrixes. The barriers to internal rotation of the OH groups were computed to be less than 4 kJ mol -1 and are easily overcome in matrixes within the family of conformers with the same heavy atom backbone. The barriers for intramolecular rearrangement of the O-C-C-O dihedral angle in both diastereomers were calculated to range from 20 to 30 kJ mol -1. Interconversions between the latter conformers were not observed in matrixes, even after annealing up to 65 K. Energy calculations, barriers, and calculated infrared spectra were carried out at the DFT(B3LYP)/6-311++G** theory. Additional MP2/ 6-311++G** calculations of energies and vibrational frequencies were performed on the most relevant conformers. Finally, independent estimations of the hydrogen-bond enthalpy in the studied molecules were also obtained based on theoretical structural data and from vibrational frequencies (using well-established empirical correlations). The obtained values for -∆H for both diastereomers of 2,3-butanediol amount to ca. 6-8 kJ mol -1 .

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“…62 This fact encouraged us to apply our approach to the study of monomeric pyrrole and its self-aggregates isolated in low-temperature inert matrixes (Ar, Xe). The spectroscopic studies were supported by extensive theoretical [DFT(B3LYP)/ 6-311++G(d,p)] structural and vibrational studies of pyrrole and their small aggregates (up to four units).…”

Section: Introductionmentioning

confidence: 99%

Self-Aggregation in Pyrrole: Matrix Isolation, Solid State Infrared Spectroscopy, and DFT Study

Gómez-Zavaglia

Fausto

2004

J. Phys. Chem. A

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Pyrrole (C 4 H 5 N) was embedded in low-temperature solid inert matrixes (argon, xenon; T ) 9 K) and both the monomer and low-order aggregates characterized by FTIR spectroscopy. The spectroscopic studies were complemented by extensive theoretical [DFT(B3LYP)/6-311++G(d,p)] structural and vibrational studies carried out for the monomer and their self-aggregates (up to four units). The calculated spectrum for monomeric pyrrole fits well those obtained immediately after deposition (at 9 K) of diluted matrixes, which can be prepared keeping the compound at low temperature before deposition and using low fluxes of the sublimate. Annealing of the matrixes to higher temperatures or increasing of the gaseous flux during deposition leads to aggregation, which can be easily recognized spectroscopically. On the basis of the theoretically predicted spectra for the monomer, dimer, trimers, and tetramers of pyrrole, assignments were proposed for the experimentally observed bands. It was also found that the formation of the hydrogen-bonded clusters shows a significant cooperativity effect, which was studied in detail and could be related with several structural and spectroscopic parameters. Infrared spectra of the pure solid compound at low temperatures in both amorphous and crystalline states were also studied and interpreted.

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Combined FTIR Matrix Isolation and Ab Initio Studies of Pyruvic Acid: Proof for Existence of the Second Conformer

Cited by 98 publications

References 37 publications

Stepwise conformational cooling towards a single isomeric state in the four internal rotors system 1,2-butanediol

Stepwise conformational cooling towards a single isomeric state in the four internal rotors system 1,2-butanediol

Conformational Study of Monomeric 2,3-Butanediols by Matrix-Isolation Infrared Spectroscopy and DFT Calculations

Self-Aggregation in Pyrrole: Matrix Isolation, Solid State Infrared Spectroscopy, and DFT Study

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