Ab initio computations on simple carbonyl compounds

George, W. O.; Jones, B.F.; Lewis, Rh.; Price, Jason M.

doi:10.1016/s0022-2860(00)00391-4

Cited by 15 publications

(15 citation statements)

References 23 publications

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“…The symbol δ denotes the increment in the relative energy with respect to the preceding level of theory, given by the higher-order correlation series HF the scaled 53 B3LYP/aug-cc-pVTZ prediction for the C-H bond in X ) H is only 64 cm -1 higher than the experimental value. Experimental data on the overtone of this band leads to a harmonic frequency of 2841.6 cm -1 (∆ν is just 3 cm -1 ), 30 which confirms the third hypothesis. Table 3 presents the results of valence FPA of 2-substituted acetaldehydes.…”

Section: Vibrational Analysis Of Tautomerssupporting

confidence: 62%

Boryl Substitution of Acetaldehyde Makes It an Enol: Inconsistency between Gn/CBS and Ab Initio/DFT Data

Balabin

2010

J. Phys. Chem. A

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Tautomerism, a particular case of isomerism, plays an important role in modern organic chemistry, biochemistry, medicinal chemistry, pharmacology, and molecular biology. Inconsistency between results of complex energy computation methods Gn/CBS (G2, G3, CBS-4M, and CBS-QB3) and high-level ab initio/DFT ones (CCSD(T)/CBS, MP2/CBS, and B3LYP/aug-cc-pVTZ) is found. Gn/CBS methods provide a qualitatively different description of tautomeric (keto-enol) equilibrium in 2-substituted acetaldehydes. According to valence focal point analysis (FPA) based on CCSD(T)/aug-cc-pVTZ, MP3/aug-cc-pVQZ, and MP2/aug-cc-pV5Z energies, boryl substitution of acetaldehyde makes it an enol. In other words, enol was found to be the global minimum on the potential energy surface (PES) of C(2)H(5)BO. Gn/CBS methods predict the keto form to be the minimum. The relative energy of alkenol, CH(BH(2))=CH(OH), is calculated to be -1.67 +/- 0.82 kcal mol(-1) at CCSD(T)/CBS level of theory. Hydrogen shift effects are also calculated in two other 2-substituted acetaldehydes, namely, 3-oxopropanenitrile (C(3)H(3)NO) and ethanal (C(2)H(4)O), with a general formula of XH(2)C-CHO (X = BH(2), CN, and H). Electron density (charge) transfer between the C=C double bond and the free p orbital of the boron atom (B) in a boryl group (BH(2)) greatly stabilizes enol with respect to ketone, CH(2)(BH(2))-CHO. The first known stabilization of enol in an acetaldehyde derivative, without an intramolecular hydrogen bond (H-bond), questions the accuracy of complex energy computation methods for boron-containing molecules. The possible reasons and consequences of this finding are discussed.

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Section: Vibrational Analysis Of Tautomerssupporting

confidence: 62%

Boryl Substitution of Acetaldehyde Makes It an Enol: Inconsistency between Gn/CBS and Ab Initio/DFT Data

Balabin

2010

J. Phys. Chem. A

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“…Harmonic wavenumber values have been determined previously for formaldehyde3 and acetaldehyde,4 from which we estimated harmonic values for acetone and compared computed and experimentally determined harmonic wavenumber values for all three carbonyl compounds. 25 These comparisons show that the accuracy of the B3LYP method is signiÐcantly greater than that of the HF method and the B3LYP/6-311&&G(2d,2p) basis set provided good agreement with the experimental values.…”

Section: Computational Methods and Resultsmentioning

confidence: 73%

Computations of medium strength hydrogen bonds–complexes of mono- and bi-functional carbonyl and nitrile compounds with hydrogen chloride

George

Jones

Lewis

et al. 2000

Phys. Chem. Chem. Phys.

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“…No rotational transitions in vibrationally excited levels of acetaldehyde were found in the ± 2 GHz spectral range around the 404 -303 transition of the vibrational ground state molecules. We attribute the existence of such highly efficient vibrational cooling in acetaldehyde to the internal CH3 rotor, with its 143 cm -1 rotor frequency [81,82], which may facilitate energy transfer between excited vibrational levels and the translational motion of the cold carrier gas [88].…”

Section: Ch3chomentioning

confidence: 99%

Chirped-pulse millimeter-wave spectroscopy for dynamics and kinetics studies of pyrolysis reactions

Prozument

Park

Shaver

et al. 2014

Phys. Chem. Chem. Phys.

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A Chirped-Pulse millimeter-Wave (CPmmW) spectrometer is applied to the study of chemical reaction products that result from pyrolysis in a Chen nozzle heated to 1000-1800 K. Millimeter-wave rotational spectroscopy unambiguously determines, for each polar reaction product, the species, the conformers, relative concentrations, conversion percentage from precursor to each product, and, in some cases, vibrational state population distributions. A chirped-pulse spectrometer can, within the frequency range of a single chirp, sample spectral regions of up to ∼10 GHz and simultaneously detect many reaction products. Here we introduce a modification to the CPmmW technique in which multiple chirps of different spectral content are applied to a molecular beam pulse that contains the pyrolysis reaction products. This technique allows for controlled allocation of its sensitivity to specific molecular transitions and effectively doubles the bandwidth of the spectrometer. As an example, the pyrolysis reaction of ethyl nitrite, CH3CH2ONO, is studied, and CH3CHO, H2CO, and HNO products are simultaneously observed and quantified, exploiting the multi-chirp CPmmW technique. Rotational and vibrational temperatures of some product molecules are determined. Subsequent to supersonic expansion from the heated nozzle, acetaldehyde molecules display a rotational temperature of 4 ± 1 K. Vibrational temperatures are found to be controlled by the collisional cooling in the expansion, and to be both species- and vibrational mode-dependent. Rotational transitions of vibrationally excited formaldehyde in levels ν4, 2ν4, 3ν4, ν2, ν3, and ν6 are observed and effective vibrational temperatures for modes 2, 3, 4, and 6 are determined and discussed.

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Ab initio computations on simple carbonyl compounds

Cited by 15 publications

References 23 publications

Boryl Substitution of Acetaldehyde Makes It an Enol: Inconsistency between Gn/CBS and Ab Initio/DFT Data

Boryl Substitution of Acetaldehyde Makes It an Enol: Inconsistency between Gn/CBS and Ab Initio/DFT Data

Computations of medium strength hydrogen bonds–complexes of mono- and bi-functional carbonyl and nitrile compounds with hydrogen chloride

Chirped-pulse millimeter-wave spectroscopy for dynamics and kinetics studies of pyrolysis reactions

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