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Deodhar B.S.,University of Missouri - Kansas City | Brenner R.E.,University of Missouri - Kansas City | Sawant D.K.,University of Missouri - Kansas City | Guirgis G.A.,College of Charleston | And 3 more authors.
Vibrational Spectroscopy | Year: 2015

The infrared spectrum (3100-300 cm-1) in the gas phase and Raman spectrum (3100-150 cm-1) of the liquid of cyclobutyldichlorosilane (c-C4H7SiHCl2) have been recorded. Variable temperature (-143 °C to -123 °C) studies of the Raman spectra (3100-300 cm-1) dissolved in liquid krypton have been carried out. From these data, the experimental stabilities of the conformer have been determined to be Eq-g > Ax-t > Eq-t > Ax-g. The enthalpy difference between Eq-g and Ax-t has been determined from band pairs to be 85 ± 10 cm-1 (1.01 ± 0.11 kJ mol-1) with the Eq-g conformer the more stable form. The enthalpy difference between Eq-g and Eq-t is 116 ± 43 cm-1 (1.39 ± 0.52 kJ mol-1) and the enthalpy difference between Eq-g and Ax-g has been determined to be 138 ± 42 cm-1 (1.66 ± 0.51 kJ mol-1) with the Eq-g conformer as the more stable form. The percentage of the equatorial gauche conformer is estimated to be 47% at ambient temperature. To support the spectroscopic study, ab initio calculations by the Møller-Plesset perturbation method to second order MP2(full) and density functional theory calculations by the B3LYP method have been carried out. The infrared intensities, Raman activities, vibrational frequencies and band contours have been predicted from MP2(full)/6-31G(d) calculations and these theoretical values are compared to the experimental ones when available. The conformational stabilities have been predicted from theoretical calculations with basis sets up to 6-311+G(2d,2p) from both MP2(full) and density functional theory calculations by the B3LYP method. The results are discussed and compared to the corresponding properties of some related molecules. © 2015 Elsevier B.V. All rights reserved. Source


Guirgis G.A.,College of Charleston | Sawant D.K.,University of Missouri - Kansas City | Brenner R.E.,University of Missouri - Kansas City | Deodhar B.S.,University of Missouri - Kansas City | And 6 more authors.
Journal of Physical Chemistry A | Year: 2015

The FT-microwave spectrum (6.5-26 GHz) of (chloromethyl)fluorosilane (ClCH2-SiH2F) has been recorded and 250 transitions for the parent species along with 13C, 37Cl, 29Si, and 30Si isotopologues have been assigned for trans conformer. Infrared spectra (3100 to 400 cm-1) of gas, solid, and the variable temperature (-100 to -60 °C) studies of the infrared spectra of the sample dissolved in xenon have been recorded. Additionally, the variable temperature (-153 to -133 °C) studies of the Raman spectra of the sample dissolved in krypton have been recorded. The enthalpy difference between the trans and gauche conformers in xenon solutions has been determined to be 109 ± 15 cm-1 (1.47 ± 0.16 kJ mol-1), and in krypton solution, the enthalpy difference has been determined to be 97 ± 16 cm-1 (1.16 ± 0.19 kJ mol-1) with the trans conformer as the more stable form. Approximately 46 ± 2% of the trans form is present at ambient temperature. By utilizing the microwave rotational constants of five isotopologues for trans and the structural parameters predicted from MP2(full)/6-311+G(d,p) calculations, adjusted r0 parameters have been obtained for trans conformer. The r0 structural parameter values for the trans form are for the heavy atom distances (Å): Si-F = 1.608 (3); C-Cl = 1.771 (3); Si-C = 1.884 (3); and angles (deg): ∠FSiC = 108.9 (5); ∠ClCSi = 104.9 (5). The results are discussed and compared to some related molecules. © 2015 American Chemical Society. Source


Durig J.R.,University of Missouri - Kansas City | Ganguly A.,College of Charleston | Zheng C.,University of Missouri - Kansas City | Gurigis G.A.,College of Charleston | And 3 more authors.
Journal of Molecular Structure | Year: 2010

Variable temperature (-55 to -131 °C) studies of the infrared spectra (4000-50 cm-1) of 2-fluoroethylamine, FCH2CH2NH2 dissolved in liquid xenon and the far infrared in liquid krypton have been carried out. From these data all five possible conformers have been identified and their relative stabilities obtained. The enthalpy differences have been determined among the most stable Gg′ conformer and the second stable conformer, Gt, to be 62 ± 8 cm-1 (0.74 ± 0.10 kJ/mol), the third stable conformer, Tg, to be 262 ± 26 cm-1 (3.14 ± 0.3 kJ/mol), the fourth most stable conformer, Tt, to be 289 ± 45 cm-1 (3.46 ± 0.5 kJ/mol) and the fifth most stable conformer, Gg to be 520 ± 50 cm-1 (6.24 ± 0.6 kJ/mol). The percentage of each conformer at ambient temperature is estimated to be with Gg′ (42 ± 4%), Gt (32 ± 1%), Tg (13 ± 1%), Tt (5 ± 1%) and Gg (3 ± 1%). The first indicator is the NCCF dihedral angle (G = gauche or T = trans) and the second one (g = gauche or t = trans) is the relative position of the lone pair of electrons on the nitrogen atom with respect to the fluorine atom. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug-cc-pVTZ for both MP2(full) and density functional theory calculations by the B3LYP method. By utilizing previously reported microwave rotational constants along with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters have been obtained for the two most stable conformers. The determined heavy atom structural parameters for the Gg′[Gt] conformer are: the distances (Å) C1-C2 = 1.509(3) [1.516(3)], C2-N3 = 1.466(3)[1.461(3)], C1-F4 = 1.400(3)[1.398(3)] and angles in degrees ∠N3C2C1 = 109.8(5) [115.5(5)], ∠F4C1C2 = 109.2(5)[109.3(5)], ∠H10N3H9 = 107.1(5) [107.1(5)](°) and τF4C1C2N3 = 65.3(5) [60.9(5)]. Vibrational assignments have been provided for most of the observed bands which have been supported by MP2(full)/6-31G(d) ab initio calculations to predict harmonic force fields, frequencies, infrared intensities, Raman activities and depolarization ratios for all five conformers. The results are discussed and compared to the corresponding properties of some similar molecules. © 2010 Elsevier B.V. All rights reserved. Source


Darkhalil I.D.,University of Missouri - Kansas City | Nagels N.,Universitair Centrum Antwerpen | Herrebout W.A.,Universitair Centrum Antwerpen | Van Der Veken B.J.,Universitair Centrum Antwerpen | And 3 more authors.
Journal of Molecular Structure | Year: 2014

FT-microwave spectroscopy was carried out where the trans conformer was identified to be the most stable conformer. Variable temperature (-60 to -100 °C) studies of the Raman spectra (4000-50 cm-1) of ethylamine, CH3CH2NH2 dissolved in liquefied xenon have been carried out. From these data both conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 62 ± 6 cm-1 (0.746 ± 0.072 kJ mol-1) with the trans conformer the more stable form. The percentage of the gauche conformer is estimated to be 60% at ambient temperature. The conformational stabilities have been predicted from ab initio calculations with the Møller-Plesset perturbation method to the second order (MP2(full)) and the fourth order (MP4(SDTQ)) as well as with density functional theory by the B3LYP method by utilizing a variety of basis sets. Vibrational assignments have been made for the observed bands which have been predicted by MP2(full)/6-31G(d) ab initio calculations which includes harmonic force fields, frequencies, infrared intensities, Raman activities and depolarization ratios for both conformers. The results are discussed and compared to the corresponding properties of some similar molecule. © 2014 Published by Elsevier B.V. Source


Darkhalil I.D.,University of Missouri - Kansas City | Klaassen J.J.,University of Missouri - Kansas City | Nagels N.,Universitair Centrum Antwerpen | Herrebout W.A.,Universitair Centrum Antwerpen | And 4 more authors.
Journal of Raman Spectroscopy | Year: 2014

Fourier transform microwave spectrum of cyclopentylamine, c-C 5H9NH2 has been recorded, and seven transitions have been assigned for the most abundant conformer, and the rotational constants have been determined: A=4909.46(5), B=3599.01(4), and C=2932.94(4). From the determined microwave rotational constants and ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters are reported with distances (Å): rCα-C β=1.529(3), rCβ-Cγ=1.544(3), rCγ-Cγ=1.550(3), rCα-N=1. 470(3), and angles ()-CCN=108.7(5), -CβCαC β=101.4(5), and τCβCαC β-Cγ-=42.0(5). The infrared spectra (4000-220cm-1) of the gas have been recorded. Additionally, the variable temperature (-60 to -100C) Raman spectra of the sample dissolved in liquefied xenon was recorded from (3800-50cm-1). The four possible conformers have been identified, and their relative stabilities obtained with enthalpy difference relative to t-Ax of 211±21cm-1 for t-Eq≥227±22cm-1 for g-Eq≥255±25cm-1 for g-Ax. The percentage of the four conformers is estimated to be 53% for the t-Ax, 11±1% for t-Eq, 20±2% for g-Ax and 16±2% for g-Eq at ambient temperature. The conformational stabilities have been predicted from ab initio calculations by utilizing several different basis sets up to aug-cc-pVTZ from both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been provided for the observed bands for all four conformers, which are predicted by MP2(full)/6-31G(d) ab initio calculations to predict harmonic force constants, wavenumbers, infrared intensities, Raman activities, and depolarization ratios for all of the conformers. The results are discussed and compared to the corresponding properties of some related molecules. Copyright © 2014 John Wiley & Sons, Ltd. Source

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