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Zheng J, Yu T, Papajak E, Alecu IM, Mielke SL, Truhlar DG. Practical methods for including torsional anharmonicity in thermochemical calculations on complex molecules: The internal-coordinate multi-structural approximation. Phys Chem Chem Phys 2011; 13:10885-907. [DOI: 10.1039/c0cp02644a] [Citation(s) in RCA: 177] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Ellingson BA, Lynch VA, Mielke SL, Truhlar DG. Statistical thermodynamics of bond torsional modes: Tests of separable, almost-separable, and improved Pitzer–Gwinn approximations. J Chem Phys 2006; 125:084305. [PMID: 16965010 DOI: 10.1063/1.2219441] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Practical approximation schemes for calculating partition functions of torsional modes are tested against accurate quantum mechanical results for H(2)O(2) and six isotopically substituted hydrogen peroxides. The schemes are classified on the basis of the type and amount of information that is required. First, approximate one-dimensional hindered-rotator partition functions are benchmarked against exact one-dimensional torsion results obtained by eigenvalue summation. The approximate one-dimensional methods tested in this stage include schemes that only require the equilibrium geometries and frequencies, schemes that also require the barrier heights of internal rotation, and schemes that require the whole one-dimensional torsional potential. Then, three classes of approximate full-dimensional vibrational-rotational partition functions are calculated and are compared with the accurate full-dimensional path integral partition functions. These three classes are (1) separable approximations combining harmonic oscillator-rigid rotator models with the one-dimensional torsion schemes, (2) almost-separable approximations in which the nonseparable zero-point energy is used to correct the separable approximations, and (3) improved nonseparable Pitzer-Gwinn-type methods in which approaches of type 1 are used as reference methods in the Pitzer-Gwinn approach. The effectiveness of these methods for the calculation of isotope effects is also studied. Based on the results of these studies, the best schemes of each type are recommended for further use on systems where a corresponding amount of information is available.
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Affiliation(s)
- Benjamin A Ellingson
- Department of Chemistry, University of Minnesota, Minneapolis, MN 55455-0431, USA
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Durig DT, Shen S, Li Y, Durig JR. Conformational stabilities and structural parameters of (CH3)(n)CH(3-n) CFO molecules. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2004; 60:1481-1504. [PMID: 15147690 DOI: 10.1016/j.saa.2003.07.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2003] [Accepted: 07/01/2003] [Indexed: 05/24/2023]
Abstract
Variable temperature (-60 to -100 degrees C) studies of the infrared spectra (3500-400 cm(-1)) of propionyl fluoride (CH3CH2CFO) and 2-methylpropionyl fluoride ((CH3)2CHCFO), dissolved in liquid xenon have been recorded. From these data, the enthalpy difference has been determined to be 329 +/- 33 cm(-1) (3.94 +/- 0.39 kJ/mol) for propionyl fluoride with the trans conformer (methyl group eclipsing the oxygen atom) more stable than the gauche form. For 2-methylpropionyl fluoride, the enthalpy difference has been determined to be 297 +/- 30 cm(-1) (3.55 +/- 0.36 kJ/mol) with the gauche conformer (methyl group eclipsing the oxygen atom) more stable than the trans form. From these DeltaH values along with assigned torsional fundamentals for both conformers and accompanying "hot bands" the potential functions governing the conformational interchange have been calculated. Utilizing the infrared data from the xenon solution and ab initio frequency predictions from MP2/6-31G* calculations, a few reassignments of the fundamentals have been made. Ab initio calculations have been carried out with several different basis sets up to MP2/6-311 + G** from which structural parameters and conformational stabilities have been determined. Additionally, force constants, infrared intensities, Raman activities, depolarization ratios, and scaled vibrational frequencies have been determined from MP2/6-31G* calculations. Adjusted structural parameters have been obtained from combined ab initio predicted values and previously reported microwave data. These parameters are compared to those obtained from either the earlier microwave and/or electron diffraction studies. Similar ab initio calculations and structural parameter determinations have been carried out for acetyl fluoride (CH3CFO) and trimethylacetyl fluoride ((CH3)3CCFO) and compared to the corresponding experimental results when appropriate.
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Affiliation(s)
- Douglas T Durig
- Departments of Chemistry and Physics, The University of the South, Sewanee, TN 37383, USA.
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Conformational stability and structural parameters of CH3CH2CClO and other (CH3)nCH3−nCClO molecules. J Mol Struct 1998. [DOI: 10.1016/s0022-2860(98)00457-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Durig J, Guirgis G, Brewer W, Little T. Vibrational spectra and structure, ab initio calculations, and conformational stability of 2-methylpropanal. J Mol Struct 1991. [DOI: 10.1016/0022-2860(91)85003-l] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Durig J, Kenton R, Phan H, Little T. Far-infrared spectra and barriers to internal rotation of pivaldehyde, pivaloyl fluoride, pivaloyl chloride and pinacolone. J Mol Struct 1991. [DOI: 10.1016/0022-2860(91)87076-t] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Far-infrared spectrum, barriers to internal rotation, structural parameters, and vibrational assignment of cyclopropylcarbonyl fluoride. J Mol Struct 1991. [DOI: 10.1016/0022-2860(91)80152-t] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Far-infrared spectrum, conformational stability, barriers to internal rotation, ab initio calculations, and vibrational assignment of propionyl bromide. J Mol Struct 1991. [DOI: 10.1016/0022-2860(91)80153-u] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Calculation of intensities of torsional transitions in vibrational spectra of molecules with internal rotation. J STRUCT CHEM+ 1991. [DOI: 10.1007/bf00752156] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Durig J, Badawi H. Spectra and structure of small ring molecules. XLV. Microwave, infrared, and Raman spectra, conformational stability, dipole moment and vibrational assignment of cyclobutylcarboxaldehyde. Chem Phys 1990. [DOI: 10.1016/0301-0104(90)89017-k] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Bell S, Guirgis G, Lin J, Durig J. Far infrared spectrum, barrier to internal rotation, r0 structure, and ab initio calculations for acetyl cyanide. J Mol Struct 1990. [DOI: 10.1016/0022-2860(90)85014-a] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Durig JR, Guirgis GA, Little TS, Stiefvater OL. Conformational stability and barriers to internal rotation of 2‐methylpropanal by far infrared and microwave spectroscopy. J Chem Phys 1989. [DOI: 10.1063/1.457126] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Stølevik R, Bakken P. Torsional potentials and conformational structures for 3-chloropropanal ClH2CCH2CHO and 3-chloropropanoyl chloride ClH2CCH2CClO and parameter values for the nonbonding interaction C(sp3) ⋯ O(carbonyl) as used in molecular-mechanics calculations. J Mol Struct 1987. [DOI: 10.1016/0022-2860(87)80050-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Durig JR, Badawi HM, Bist HD, Little TS. Spectra and structure of small ring molecules. XLVII. Rotational and vibrational spectra and conformational stability of cyclobutylcarboxylic acid fluoride. J Chem Phys 1986. [DOI: 10.1063/1.451555] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Guirgis G, Little T, Badawi H, Durig J. Microwave spectrum and conformational stability of isopropyl carboxaldehyde. J Mol Struct 1986. [DOI: 10.1016/0022-2860(86)85071-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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van der Veken BJ, Coppens P, Johnson RD, Durig JR. Spectra and structure of organophosphorus compounds. XXIV. Microwave, infrared, and Raman spectra, conformational stability, and vibrational assignment for chloromethylphosphonic difluoride. J Chem Phys 1985. [DOI: 10.1063/1.449388] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Durig J, Bist H, Furic K, Qiu J, Little T. Far infrared spectra and barriers to internal rotation of benzaldehyde, benzoyl fluoride, benzoyl chloride and acetophenone. J Mol Struct 1985. [DOI: 10.1016/0022-2860(85)80191-5] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Durig J, Badawi H, Little T, Cuirgis G, Kalasinsky V. Spectra and structure of small ring molecules. J Mol Struct 1984. [DOI: 10.1016/0022-2860(84)85021-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Durig JR, Zhen M, Little TS. Determination of the conformational barriers to internal rotation of 3‐fluoropropene from far infrared and low frequency Raman spectra. J Chem Phys 1984. [DOI: 10.1063/1.447434] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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