Structure elucidation and photochemistry of substituted carboxylic compounds by low temperature matrix-isolation and solid state vibrational spectroscopy

Fausto, Rui; Maçôas, Ermelinda; Kulbida, A.

doi:10.1016/s0022-2860(98)00654-1

Cited by 9 publications

(22 citation statements)

References 31 publications

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“…The mechanisms of the photolysis processes cannot be unequivocally established on the basis of the experiments here described. However the photochemical reactions shall involve radical intermediates resulting from a-cleavages either of the C-C a bond or C-O bond, as found previously for most of the carboxylic acids that undergo decarboxylation or decarbonylation reactions upon UV irradiation [31][32][33][34][35][36]. This indicates that the decomposition reactions shall take place mainly on the excited state surfaces rather than in the vibrationally excited ground state.…”

Section: Resultsmentioning

confidence: 56%

Entropy effects in conformational distribution and conformationally dependent UV-induced photolysis of serine monomer isolated in solid argon

Jarmelo

Fausto

2006

Journal of Molecular Structure

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Monomeric serine can be trapped in low temperature argon matrices in different conformers, which can be classified in three groups (A, B, C) accordingly to the main intramolecular interaction they exhibit: A (OH A /N hydrogen bond), B (OH C /N) and C (OH A /Oa) (subscripts A and C stand for alcohol and carboxylic group, respectively). The OH C /N intramolecular interaction found in B-type conformers is considerably stronger than both the OH A /N and OH A /Oa hydrogen bonds, and leads to reduce the abundance of B-type form relatively to A and C forms at high temperatures due to entropy effects. When submitted to UV irradiation (lO200 nm), the main observed photoprocess is decarboxylation, leading to production of CO 2 and ethanolamine. A less important photochemical process is also observed, where the compound undergoes decarbonylation, with formation of CO, H 2 O and acetamide. The two observed photoprocesses were found to be dependent on the conformation assumed by the reactant molecule, with Aand C-type conformers of serine undergoing decarboxylation and B-type conformers decarbonylation.

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Section: Resultsmentioning

confidence: 56%

Entropy effects in conformational distribution and conformationally dependent UV-induced photolysis of serine monomer isolated in solid argon

Jarmelo

Fausto

2006

Journal of Molecular Structure

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“…[10][11][12] Detailed structural and vibrational studies were reported for the monocarboxylic parent molecule, propenoic acid (acrylic acid, CH 2 dCHCOOH), 13 and the related molecules, (Z)-and (E)-3-methyl-propenoic [(Z)-and (E)-crotonic acid, CH 3 CHdCHCOOH]. 14,15 These studies revealed that these molecules exist both in the gas phase and in solid argon in two conformational states differing by internal rotation around the C R -C bond and having similar energies [∆E (s-trans)-(s-cis) ≈ 3 kJ mol -1 ]. The s-cis conformer (CdC R -CdO dihedral equals to 0°) was found to be the conformational ground state for the three molecules.…”

Section: Introductionmentioning

confidence: 99%

A Matrix Isolation Spectroscopic and Quantum Chemical Study of Fumaric and Maleic Acid

et al. 2001

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Relative energies and vibrational spectra of buthenedioic acid [(E)-and (Z)-HOOC-CHdCH-COOH; fumaric and maleic acids] were calculated using Hartree-Fock (HF), Møller-Plesset to 2nd order (MP2), and B3LYP Density Functional Theory (DFT) levels of approximation. Computationally the lowest energy conformer of maleic acid has a nearly planar structure with an OH‚‚‚OdC intramolecular hydrogen bond closing a seven member OdC-C(H)dC(H)-CO -H ring. Second conformer of maleic acid adopts a cis arrangement around the CO bonds and exhibits the two carbonyl bonds in a nearly orthogonal arrangement with one carboxylic group in the plane containing the carbon atoms. Fumaric acid has three planar conformers with relative energies within 5 kJ mol-1. These conformers exhibit a cis arrangement around the CO bond and differ by the relative conformation of their OdC-CdC axes. The infrared spectra of the studied compounds isolated in a solid argon matrix feature the most stable conformers. Narrowband tunable irradiation in the near-infrared region (6901 cm-1) was found to promote a conversion of the second most stable conformer of maleic acid into the most stable conformer.

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“…3,6 The individual molecules belong to the C 2 symmetry point group, with both carboxylic groups out of the plane of the carbon atoms adopting the cis arrangement around the C-O bond ( Figure 1). 7 Monomeric malonic acid and its monoanion have been studied previously by Hartree-Fock ab initio self-consistent field (SCF)-molecular orbital (MO) calculations using smallsize basis sets (STO-3G and 4-21G) in order to explain the large dissociation constant ratio k 1 /k 2 . This ratio is usually exhibited by dicarboxylic acids where the monoanion can be stabilized by intramolecular hydrogen bonding.…”

Section: Introductionmentioning

confidence: 99%

Conformational Analysis and Near-Infrared-Induced Rotamerization of Malonic Acid in an Argon Matrix

Maçôas¹,

Fausto²,

Lundell³

et al. 2000

J. Phys. Chem. A

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Relative energies and vibrational spectra of the conformational states of a malonic acid monomer (HOOCCH 2 -COOH) were calculated using various levels of approximation [Hartree-Fock (HF), Møller-Plesset to second order (MP2), and B3LYP density functional theory (DFT)]. The calculations predict the existence of six different conformers according to skeletal C-C bond and O-H bond rotation. Three conformers are found with energies close enough to enable their spectroscopic observation. The lowest-energy conformer (I) shows a nearly planar structure with an OH‚‚‚OdC intramolecular hydrogen bond closing a six-member OdC-CH 2 -C-O-H ring. The second-and third-lower energy conformers (II and III) differ from the conformational ground state by less than 5 kJ mol -1 . Conformers II and III adopt a cis arrangement around the C-O bonds: conformer II exhibits the two carbonyl bonds in a nearly orthogonal arrangement, with one carboxylic group in the plane containing the carbon atoms, whereas in conformer III (C 2 symmetry), the carbonyl bonds make a dihedral angle of ca. 120°, and both carboxylic groups are placed out of the plane containing the skeletal carbons. Their relative energy is predicted by the highest-level calculations to be ca. 1 kJ mol -1 . The theoretical predictions agree with the analysis of the infrared spectra of monomeric malonic acid isolated in a solid argon matrix, where the presence of the three above-mentioned conformers was unequivocally identified. Narrowband tunable irradiation in the near-infrared region was found to promote efficiently the interconversion between the experimentally observed conformers.

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Structure elucidation and photochemistry of substituted carboxylic compounds by low temperature matrix-isolation and solid state vibrational spectroscopy

Cited by 9 publications

References 31 publications

Entropy effects in conformational distribution and conformationally dependent UV-induced photolysis of serine monomer isolated in solid argon

Entropy effects in conformational distribution and conformationally dependent UV-induced photolysis of serine monomer isolated in solid argon

A Matrix Isolation Spectroscopic and Quantum Chemical Study of Fumaric and Maleic Acid

Conformational Analysis and Near-Infrared-Induced Rotamerization of Malonic Acid in an Argon Matrix

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