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Guirgis GA, Overby JS, Barker TJ, Palmer MH, Pate BH, Seifert NA. The Molecular Structure of Methylfluoroisocyanato Silane: A Combined Microwave Spectral and Theoretical Study. J Phys Chem A 2015; 119:652-8. [PMID: 25551546 DOI: 10.1021/jp511354j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Gamil A. Guirgis
- Chemistry & Biochemistry, College of Charleston, Charleston, South Carolina 29424, United States
| | - Jason S. Overby
- Chemistry & Biochemistry, College of Charleston, Charleston, South Carolina 29424, United States
| | - Timothy J. Barker
- Chemistry & Biochemistry, College of Charleston, Charleston, South Carolina 29424, United States
| | - Michael H. Palmer
- School
of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, U.K
| | - Brooks H. Pate
- Department
of Chemistry, University of Virginia, McCormick Road,
P.O. Box 400319, Charlottesville, Virginia 22904-4319, United States
| | - Nathan A. Seifert
- Department
of Chemistry, University of Virginia, McCormick Road,
P.O. Box 400319, Charlottesville, Virginia 22904-4319, United States
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2
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Das U, Raghavachari K. Predicting PH vibrations of gas phase molecules and surface-adsorbed species using bond length-frequency correlations. J Comput Chem 2009; 30:1872-81. [DOI: 10.1002/jcc.21187] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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3
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Carteret C. Vibrational properties of silanol group: from alkylsilanol to small silica cluster. Effects of silicon substituents. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2006; 64:670-80. [PMID: 16677854 DOI: 10.1016/j.saa.2005.08.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2005] [Revised: 07/26/2005] [Accepted: 08/02/2005] [Indexed: 05/09/2023]
Abstract
Structural and vibrational features of silanol group are investigated in detail by quantum calculations and normal mode analysis. The structural parameters, charge distributions, force fields, vibrational wavenumbers, potential energy distributions of normal modes and derivatives of the electric dipole moment are analyzed in relation to the nature of the substituents adjacent to the silanol group. The calculations results are discussed in light of available experimental data. Although the OH stretching mode has already been well localized in various silanols, both the Si-(OH) stretching and SiOH bending vibrations have not been yet finely analyzed leading to some discrepancies reported in literature. Clarified assignments of these vibrations are proposed on the basis of normal mode analysis and of SiOH-->SiOD isotopic exchange. The following spectral ranges are determined: 790-1030 cm-1 for nuSi-(OH), 790-1010 cm-1 for nuSi-(OD), 790-900 cm-1 for deltaOH and 580-640 cm-1 for deltaOD. The nuSi-(OH)/nuSi-(OD) wavenumbers are highly dependent on silicon substituents: electron-withdrawing groups induce shifts to higher wavenumbers while electron-releasing groups induce shifts to lower wavenumbers. In alkylsilanols, the SiOH bending is observed at higher wavenumber than the stretching vibration. Analysis of infrared intensities and dipole derivatives in internal coordinates gives explanations to spectral "anomalies" observed in experimental measurements such as well defined and intense nuSi-(OD) absorption in contrast with very low intensity for nuSi-(OH). Numerous empirical correlations are established allowing reconstruction of both SiOH force field and SiOH structural parameters with knowledge of few experimental data.
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Affiliation(s)
- Cédric Carteret
- Laboratoire de Chimie Physique pour l'Environnement, Equipe Chimie et Spectrochimie des Interfaces, UMR 7564 CNRS-Université Henri Poincaré, 405 rue de Vandoeuvre, 54600 Villers-lès-Nancy, France.
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Emsley JW, Longeri M, Merlet D, Pileio G, Suryaprakash N. An investigation of the structure and bond rotational potential of some fluorinated ethanes by NMR spectroscopy of solutions in nematic liquid crystalline solvents. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2006; 180:245-55. [PMID: 16554180 DOI: 10.1016/j.jmr.2006.03.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2006] [Revised: 02/24/2006] [Accepted: 03/01/2006] [Indexed: 05/07/2023]
Abstract
NMR spectra of 1,2-dibromo-1,1-difluoroethane and 1-bromo-2-iodo-tetrafluoroethane dissolved in nematic liquid crystalline solvents have been analysed to yield the magnitudes and signs of the scalar couplings, J(ij), and total anisotropic couplings, T(ij), between all the (1)H, (19)F, and (13)C nuclei, except for those between two (13)C nuclei. The values obtained for T(ij) in principle contain a contribution from J(ij)(aniso), the component along the static applied magnetic field of the anisotropic part of the electron-mediated spin-spin coupling. Neglecting this contribution allows partially averaged dipolar couplings, D(ij), to be extracted from the T(ij), and these were used to determine the structure, orientational order, and the conformational distribution generated by rotation about the C-C bond. The values obtained are compared with the results of calculations by ab initio and density functional methods. The differences found are no greater than those obtained for similar compounds which do not contain fluorine, so that there is no definitive evidence for significant contributions from J(CF)(aniso) or J(FF)(aniso) in the two compounds studied.
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Affiliation(s)
- J W Emsley
- Department of Chemistry, Universita della Calabria, Arcavacata di Rende, Italy.
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Black KA, Wilsey S, Houk KN. Dissociative and associative mechanisms of cope rearrangements of fluorinated 1,5-hexadienes and 2,2'-bis-methylenecyclopentanes. J Am Chem Soc 2003; 125:6715-24. [PMID: 12769581 DOI: 10.1021/ja021330h] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The effects of fluorine substitution on the Cope rearrangements of 1,5-hexadiene and 2,2'-bis-methylenecyclopentane have been examined computationally using (U)B3LYP/6-31+G(d,p) and CASPT2/6-31G(d) methodology. The calculations indicate that fluorine substituents at the hexadiene termini generally stabilize the transition states relative to the ground states of the chair conformations and destabilize pathways that occur via boat conformations, in accord with the experimental observations of Dolbier. With meso-2,2'-bis(difluoromethylene)cyclopentane, this destabilization is sufficient to favor a relatively dissociative concerted transition state resembling weakly interacting allyl radicals over a normal aromatic concerted boat transition state. This preference is due partly to an increase in the activation enthalpy for the concerted rearrangement coupled with the more favorable entropy for dissociation. In octafluoro- and decafluorohexadienes, the situation is reversed, and reaction through a cyclohexane-1,4-diyl is favored. Even in the octafluoro system with no radical stabilizing substituents at C(2) and C(5), the preference of fluorine for sp(3) centers causes reaction via the cyclohexane-1,4-diyl. In establishing methodology for this study, the conformations of 1,2-difluoroethane and 1,1,2,2-tetrafluoroethane were also examined thoroughly by the B3LYP method using three basis sets.
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Affiliation(s)
- Kersey A Black
- Joint Science Department, Claremont Colleges, Claremont, CA 91711-5916, USA
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Quiñónez PB, Vila A, Graña AM, Mosquera RA. AIM study on the influence of fluorine atoms on the alkyl chain. Chem Phys 2003. [DOI: 10.1016/s0301-0104(02)00993-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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7
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McKean D. Quantum-chemical studies of ethyl fluoride: structure, scaled force fields and electrical properties. J Mol Struct 2002. [DOI: 10.1016/s0022-2860(02)00133-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Fleischer H, McKean DC, Torto I. A quantum-chemical study of the structure, vibrations and SiH bond properties of disilylamine, NH(SiH3)2. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2002; 58:911-925. [PMID: 11942397 DOI: 10.1016/s1386-1425(01)00566-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Quantum-chemical calculations at HF, MP2 and B3LYP levels with 6-31G* and 6-311G** basis sets are reported for disilylamine, NH(SiH3)2. The equilibrium structure is found to vary with both level and basis set, all but one of the structures exhibiting a small lack of planarity of the HNSi2 system. The barrier to inversion, however, is found to be very low, at most 38 cm(-1). Vibration frequencies and intensities are calculated. The frequencies are scaled, where possible, either using updated infrared data or with the aid of factors transferred from N(CH3)(SiH3)2. Unobserved frequencies due to the v(s)NSi2, deltaNSi2 and delta(perpendicular)NH modes are predicted near 610, 210 and 360 cm(-1), respectively. The lower silyl torsion lies below 40 cm(-1). The appearance of a single broad vSiH band in gas-phase samples of both NH(SiH3)2 and NH(SiH3)(SiD3) is suggestive of signal averaging due to internal rotation. The frequencies v(is)SiH, infrared intensities and Raman scattering activities of the bands due to an isolated SiH bond in an otherwise deuterated species are calculated and correlated with the torsional angle of this bond and with the Mulliken charge on the hydrogen atom. The strength of the bond is a minimum, and the infrared intensity and Raman scattering activity are maxima, when the bond direction is roughly orthogonal to the skeletal plane. A major part of the frequency and intensity variations is attributed to n(p)(N)-sigma*(Si-H)) hyperconjugation which, NBO calculations show, reaches a maximum for this conformation. However, systematic smaller variations are found for SiH bonds lying in the skeletal plane, which reflect the proximity of the other silyl group and only partly correlate with Mulliken charge. vSiH-vSiH interaction force constants, f', are calculated for pairs of SiH bonds in different silyl groups and compared with the corresponding dipole-dipole potential energy, the latter calculated using a classical treatment of the interaction between point dipoles arising from delta mu/delta r for the SiH bonds involved. The gradient of the correlation is very close to that expected from the theory, but a negative intercept indicates the presence of additional factors.
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Affiliation(s)
- Holger Fleischer
- Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg Universität, Germany
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Fleischer H, McKean DC, Torto I, Boggs JE. Infrared and quantum-chemical studies of the structure and vibrations of methyldisilylamine. J Mol Struct 2002. [DOI: 10.1016/s0022-2860(01)00667-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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10
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McKean DC, Torto I. Infrared and quantum-chemical studies of the structure and vibrations of trisilylamine. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2001; 57:1725-1738. [PMID: 11506023 DOI: 10.1016/s1386-1425(01)00386-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
New infrared spectra are reported for variously labelled trisilylamines. Quantum-chemical (QC) calculations of structure and force field have been made at HF, MP2 and B3LYP levels, each with the 6-31G* and 6-311G** basis sets. At each level, a minimum in the potential surface occurs at the C3h configuration. No evidence was found for a significant variation in SiH bond length with orientation. The appearance of two bands in the infrared spectrum of N(SiH3)3 in the 2nuSiH region is explained by local mode theory in terms of transitions to (200) and (110) levels. In the gas phase, signal averaging appears to occur in the nuSiH region in the infrared spectrum, but not in the Raman. In solid films, both IR and Raman spectra indicate the presence of a range of SiH bond strengths, corresponding to an absence of any site symmetry. Each complete QC calculated force field was fitted to the frequencies observed for N(SiH3)3 and N(SiD3)3, using nine independent scale factors. An interaction force constant between nu(as)NSi3 and delta(s)SiH3 motions required further adjustment. Unobserved frequencies in the d0 and d9 species are predicted. The out-of-plane skeletal bending mode is expected to lie between 170 and 200 cm(-1). Unscaled SiH3 torsional frequencies vary from 64 cm(-1) upwards. The effect of the presence of three internal rotors on the spectra throughout calls for theoretical study.
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Affiliation(s)
- D C McKean
- Department of Chemistry, University of Edinburgh, UK.
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McKean DC. Quantum-Chemical Studies of Fluoroethanes: Vibrational Assignments, Isolated CH Stretching Frequencies, Valence Force Constants, and Bond Length Relationships. J Phys Chem A 2000. [DOI: 10.1021/jp001605k] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Donald C. McKean
- Department of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, U.K
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Palmer M. On the charge distribution in ethanes and disilanes and correlations with equilibrium bond lengths; an ab initio study. ACTA ACUST UNITED AC 2000. [DOI: 10.1016/s0166-1280(00)00391-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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