Rotational barriers of 2-acetylthiophene and related carbonyl compounds

Miyahara, Yuji; Inazu, Toshiyuki

doi:10.1016/0166-1280(95)04470-1

Cited by 12 publications

(4 citation statements)

References 23 publications

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“…The conformer with the larger dipole moment, OO-cis, dominates in polar solvents over the OO-trans conformer, which is, however, more stable in the gas phase or in low-polarity solvents (dielectric constant smaller than 5). The small energy difference between the two conformations and the activation barrier of furfural in different solvents have attracted both experimental 2-15 and theoretical investigations. − Bain and Hazendonk 14 have used combined NMR experiments to determine the activation barrier of furfural in toluene, acetone, and methanol. They have found that the behavior of the enthalpies of activation for the cis−trans process does not obey a simple relationship with the dielectric constant.…”

Section: Introductionmentioning

confidence: 98%

“…The conformational equilibrium of furfural, however, has a strong solvent dependence. , In neat furfural the barrier is 3 11.0 kcal/mol. The barrier has also been determined for a few other solvents and it has been the subject of intense theoretical and experimental investigations. − The recent and interesting work of Baldridge, Jonas, and Bain 7 gives an overview of previous works on the energetics of furfural in the gas phase and in different solvents. The conformer with the larger dipole moment, OO-cis, dominates in polar solvents over the OO-trans conformer, which is, however, more stable in the gas phase or in low-polarity solvents (dielectric constant smaller than 5).…”

Section: Introductionmentioning

confidence: 99%

“…The small energy difference between the two conformations and the activation barrier of furfural in different solvents have attracted both experimental [2][3][4][5][6][7][8][9][10][11][12][13][14][15] and theoretical investigations. [15][16][17][18][19][20] Bain and Hazendonk 14 have used combined NMR experiments to determine the activation barrier of furfural in toluene, acetone, and methanol. They have found that the behavior of the enthalpies of activation for the cis-trans process does not obey a simple relationship with the dielectric constant.…”

Section: Introductionmentioning

confidence: 99%

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A Monte Carlo-Quantum Mechanics Study of the Solvent-Induced Spectral Shift and the Specific Role of Hydrogen Bonds in the Conformational Equilibrium of Furfural in Water

2002

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The solvation shift of the lowest absorption transition of furfural in water is analyzed as a function of the rotation angle for the interconversion between the two conformations, OO-cis and OO-trans, of furfural. In total, 20 Monte Carlo NPT simulations are performed, corresponding to different rotation angles of the carbonyl group. The solvation shift of the n−π* state is calculated to be 1230 ± 45 cm-1 in the most stable OO-cis form. This calculated shift is found to be essentially independent of the rotation angle. The hydrogen bonds between furfural and water are also analyzed along the interconversion path. These hydrogen bonds are found to be equivalent, both in number and in binding energy, for all rotation angles. The results for the solvent-induced spectral shift and the hydrogen bond interactions confirm that in water they make no preference for any rotamer of furfural and lead to small contribution to the entropic activation barrier of furfural in protic solvents.

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Monte Carlo-Quantum Mechanics Study of the Solvent-Induced Spectral Shift and the Specific Role of Hydrogen Bonds in the Conformational Equilibrium of Furfural in Water

2002

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“…Study of the internal rotation barrier of a molecule has received increasing interest since it conveys information regarding intramolecular interactions and molecular electronic structure. Previous calculations of the internal rotation of molecules were mostly on their twofold or threefold barriers 1–5, and these barriers are several kilocalorie/mole, and calculated barriers were dependent on the calculation methods 1–5. Relatively few theoretical studies 6–9 have discussed molecules having sixfold barriers since these barriers are very low.…”

Section: Introductionmentioning

confidence: 99%

Theoretical study on the molecular structures of toluene, para-fluorotoluene, para-chlorotoluene, and 4-methylpyridine and their sixfold internal rotational barriers

Chen¹,

Chang²

2000

Int. J. Quant. Chem.

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Two kinds of sixfold internal rotational configurations of toluene, para-fluorotoluene, para-chlorotoluene, and 4-methylpyridine were calculated using Hartree-Fock (HF), second-order Møller-Plesset (MP2), and Beck's three parameter hybrid functional using the LYP correlation functional (B3LYP) theory methods with various high-level basis sets. Structures and energies were compared for different configurations. Calculations indicate that the orthogonal configuration has a local minimum while the planar configuration is a transition structure. Furthermore, geometries of the orthogonal and the planar configurations are quite similar, except for a methyl CH bond. Sixfold internal rotational barriers were calculated from the energy difference of two different configurations. For the calculated results, HF methods underestimated the rotational barriers, but MP2 calculations overestimated them. However, the density functional theory (DFT) method is a reliable method since the calculated internal rotational barriers are similar to the experimental ones.

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NMR Spectroscopy Investigation of the Cooperative Nature of the Internal Rotational Motions in Acetophenone

Longeri

Pileio

et al. 2005

ChemPhysChem

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The proton NMR spectrum of the doubly enriched acetophenone-carbonyl,methyl-13C2 isotopomer dissolved in a liquid-crystalline solvent (LXNMR) was analyzed to yield a data set of 19 dipolar couplings. The presence of so many couplings, and in particular the dependence of some of them on the acetyl carbons enabled the investigation of the structure of the acetyl moiety and of possible cooperative motions about the aryl-carbonyl and carbonyl-methyl bonds. Methodological aspects, and approximations relating to the application of the vibrational correction procedure in the presence of large-amplitude torsional motions, are discussed. Results show that it is possible to discriminate between a continuous and a discrete conformer distribution about the angle phi(1) but not among a few proposed continuous shapes of U(iso)({phi}). In this study, the use of dipolar couplings with a non-negligible contribution from the indirect spin-spin coupling tensor J, (D(C8C9) in our case), for structural determination is extended from rigid to flexible molecules. The 1/2J(aniso)(C8C9) contribution was derived theoretically using the density functional theory linear response (DFT-LR) first-principles calculation of the J(C8C9) spin-spin coupling tensor.

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Rotational barriers of 2-acetylthiophene and related carbonyl compounds

Cited by 12 publications

References 23 publications

A Monte Carlo-Quantum Mechanics Study of the Solvent-Induced Spectral Shift and the Specific Role of Hydrogen Bonds in the Conformational Equilibrium of Furfural in Water

A Monte Carlo-Quantum Mechanics Study of the Solvent-Induced Spectral Shift and the Specific Role of Hydrogen Bonds in the Conformational Equilibrium of Furfural in Water

Theoretical study on the molecular structures of toluene, para-fluorotoluene, para-chlorotoluene, and 4-methylpyridine and their sixfold internal rotational barriers

NMR Spectroscopy Investigation of the Cooperative Nature of the Internal Rotational Motions in Acetophenone

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