R0 Structural parameters, conformational, vibrational studies and ab initio calculations of cyanocyclopentane.

The infrared and Raman spectra (3100-50 cm(-1)) of the gas, liquid or solution, and solid have been recorded of cyanocyclopentane, c-C5H9CN. Variable temperature (-60 to -100°C) studies of the infrared spectra (3100-400cm(-1)) of the sample dissolved in liquid xenon have been carried out. From these data, both the envelope-equatorial (Eq) and Ax conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 55 ± 12 cm(-1) (0.66 ± 0.14 kJ/mol) with the Eq conformer the more stable form. The percentage of the Ax conformer is estimated to be 45±1% 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 made for the observed bands for both conformers with initial predictions by MP2(full)/6-31G(d) ab initio calculations to obtain harmonic force constants, wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. The r0 structural parameter values for the Eq[Ax] form are; for the heavy atom distances (Å): CN=1.160 [1.160] (3); Cα-C=1.463 [1.463] (3); Cα-Cß, Cß'=1.543 [1.545] (3); Cß-Cγ, Cγ'=1.540 [1.541] (3); Cγ-Cγ'=1.552 [1.553] (3) and angles (°): ∠Cα-CN=179.0 [178.9] (5); ∠CßCα-C=113.1 [110.1] (5); ∠CßCαCß'=103.0 [102.1] (5); ∠CαCßCγ=104.1 [104.8] (5); ∠CßCγCγ'=106.3 [106.0] (5). The results are discussed and compared to the corresponding properties of some related molecules.

Microwave, structural, conformational, vibrational studies and ab initio calculations of fluoroacetyl chloride.

The infrared and Raman spectra (3200-50 cm(-1)) of the gas, liquid or solution, and solid of fluoroacetyl chloride, FCH2COCl have been recorded. FT-microwave studies have also been carried out and 22 transitions were recorded for the trans conformer. Variable temperature (-50 to -105 °C) studies of the infrared and Raman spectra (3200-50 cm(-1)) of xenon solutions have been carried out. From these data, the trans, cis and gauche conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 159±11 cm(-1) (1.90±0.14 kJ mol(-1)) with the trans conformer the more stable form than the cis. The energy difference between the cis and gauche form is 222±18 cm(-1) (2.66±0.21 kJ/mol) and the energy difference between the trans and gauche forms is 386±13 cm(-1) (4.61±0.16 kJ/mol). Vibrational assignments have been made for the observed bands for the three conformers with initial predictions by MP2(full)/6-31G(d) ab initio calculations to obtain harmonic force constants, wavenumbers, infrared intensities, and Raman activities for the three conformers. By utilizing the microwave rotational constants of two isotopomers for trans, combined with the structural parameters predicted from MP2(full)/6-311+G(d,p) calculations, adjusted r0 parameters have been obtained for the trans conformer. The results are discussed and compared to the corresponding properties of some related molecules.

Microwave, structural, conformational, vibrational studies and ab initio calculations of isocyanocyclopentane.

The infrared and Raman spectra (3200-50 cm(-1)) of the gas, liquid or solution, and solid have been recorded of isocyanocyclopentane, c-C5H9NC. FT-microwave studies have also been carried out and 23 transitions were recorded for the envelope-axial (Ax) conformer. Variable temperature (-65 to -100 °C) studies of the infrared spectra (3200-400 cm(-1)) dissolved in liquid xenon have been carried out. From these data, both the Ax and envelope-equatorial (Eq) conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 102±10 cm(-1) (1.21±0.11 kJ mol(-1)) with the Ax conformer the more stable form. The percentage of the Eq conformer is estimated to be 38±1% 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 made for the observed bands for both conformers with initial predictions by MP2(full)/6-31G(d) ab initio calculations to obtain harmonic force constants, wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. The structural parameter values for the Ax form are; for the heavy atom distances (Å): C≡N = 1.176 (3); Cα-N=1.432 (3); Cα-Cß,Cß'=1.534 (3); Cß-Cγ,Cγ'=1.542 (3); Cγ-Cγ'=1.554 (3) and angles (°):∠Cα-N≡C=177.8 (5); ∠CßCα-N=110.4 (5);

Microwave and infrared spectra, adjusted r0 structural parameters, conformational stabilities, vibrational assignments, and theoretical calculations of cyclobutylcarboxylic acid chloride.

The FT-microwave spectrum of cyclobutylcarboxylic acid chloride, c-C4H7C(O)Cl, has been recorded and 153 transitions for the (35)Cl and (37)Cl isotopologues have been assigned for the gauche-equatorial (g-Eq) conformation. The ground state rotational constants were determined for (35)Cl [(37)Cl]: A = 4349.8429(25) [4322.0555(56)] MHz, B = 1414.8032(25) [1384.5058(25)] MHz, and C = 1148.2411(25) [1126.3546(25)] MHz. From these rotational constants and ab initio predicted parameters, adjusted r0 parameters are reported with distances (Å) rCα-C = 1.491(4), rC═O = 1.193(3), rCα-Cß = 1.553(4), rCα-Cß' = 1.540(4), rCγ-Cß = 1.547(4), rCγ-Cß' = 1.546(4), rC-Cl = 1.801(3) and angles (deg) τCγCßCß'Cα = 30.9(5). Variable temperature (-70 to -100 °C) infrared spectra (4000 to 400 cm(-1)) were recorded in liquid xenon and the g-Eq conformer was determined the most stable form, with enthalpy differences of 91 ± 9 cm(-1) (1.09 ± 0.11 kJ/mol) for the gauche-axial (g-Ax) form and 173 ± 17 cm(-1) (2.07 ± 0.20 kJ/mol) for the trans-equatorial (t-Eq) conformer. The relative amounts at ambient temperature are 54% g-Eq, 35 ± 1% g-Ax, and 12 ± 1% t-Eq forms. Vibrational assignments have been provided for the three conformers and theoretical calculations were carried out. The results are discussed and compared to corresponding properties of related molecules.

Raman and infrared spectra, r0 structural parameters, and vibrational assignments of (CH3)2PX where X=H, CN, and Cl.

The infrared (3500-80 cm(-1)) and Raman spectra (3500-40 cm(-1)) of gas/or liquid and solid (CH(3))(2)PX with X=H (DMH), CN (DMCN) and Cl (DMCl) as well as (CD(3))(2)PH have been recorded and complete vibrational assignments are given for all three molecules. 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 quantities are compared to experimental ones when available. By utilizing the previously reported microwave rotational constants for DMH and DMCN along with the MP2(full)/6-311+G(d,p) predicted values, adjusted r(0) structural parameters for DMH and DMCN have been determined. The heavy atom parameters for DMH are: r(0)(P-C(3,4))=1.8477(30)Å, ∠CPC=99.88(50)° and for DMCN: r(0)(N-C)=1.159(3), r(0)(C-P)=1.790(3), r(0)(P-C(4,5))=1.841(3)Å, ∠NCP=175.7(5), ∠CPC(4,5)=97.9(5) and ∠CPC=100.7(5)°. Barriers to internal rotation are reported. The experimental values are compared to the corresponding values of some similar molecules whenever possible.

Structure and conformation studies from temperature dependent infrared spectra of xenon solutions and ab initio calculations of cyclobutylgermane.

The infrared spectra (3500-220 cm(-1)) of cyclobutylgermane, c-C(4)H(7)GeH(3) have been recorded of the gas. Also variable temperature (-65 to -100 °C) studies of the infrared spectra (3500-400 cm(-1)) of the sample dissolved in liquid xenon were recorded and both the equatorial and axial conformers were identified. The enthalpy difference has been determined from 10 band pairs 8 temperatures to give 112 ± 11 cm(-1) (1.34 ± 0.13 kJ mol(-1)) with the equatorial conformer the more stable form. The percentage of the axial conformer present at ambient temperature is estimated to be 37 ± 1%. From ab initio calculations conformational stabilities have been predicted from both MP2(full) and density functional theory calculations from a variety of basic sets. The r(0) structure parameters have been obtained for both conformers from the previously reported rotational constants from the three isotopologues. The determined heavy atom distances for the equatorial [axial] form are (Å) Ge-C(α)=1.952(3) [1.950(3)], [Formula: see text] , [Formula: see text] [1.551(3)] and angles in degrees (°) ∠GeC(α)C(ß)=118.6(5) [113.4(5)], [Formula: see text] , ∠C(α)C(ß)C(γ)=87.8(5) [88.8(5)], [Formula: see text] and a puckering angle of 29.1(5) [25.1(5)]. Data from ab initio calculations were used to predict vibrational harmonic force constants, fundamental wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. The results are compared to the corresponding properties of some related molecules.

Microwave, infrared, and Raman spectra, r0 structural parameters, conformational stability, and vibrational assignment of allyl thiol.

FT-microwave spectrum of allyl thiol, H(2)CCHCH(2)SH, has been recorded, and 19 transitions have been assigned for the most abundant isotopologue of Gg conformer, and the rotational constants have been determined; A=20,041.439 (4), B=2795.830 (1), C=2701.084 (1). From the determined microwave rotational constants and ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r(0) parameters are reported with distances (Å): rCC=1.343 (3), rC-C=1.496 (3), rC-S=1.827 (3) and angles (°) ∠CCC=123.4 (5), ∠CCS=112.5 (5), and τC(γ)C(ß)C(α)S=118.7 (5). Variable temperature (-55 to -100°C) infrared spectra (3600-400cm(-1)) were recorded of allyl thiol in liquid xenon and the Gg conformer was determined to be the most stable form. The enthalpy differences relative to the Gg form are for Cg 120±9cm(-1) (1.44±0.11kJ/mol), for Gg' 337±34cm(-1) (4.03±0.41kJ/mol), and for Gt 360±36cm(-1) (4.31±0.43kJ/mol). The relative amounts present at ambient temperature are Gg 52±1%, Cg 29±1%, Gg' 10±1%, and Gt 9±1%. The conformational stabilities have been predicted from ab initio calculations with many basis sets up to aug-cc-pVTZ and the predicted stabilities are in agreement with the experimentally determined order. Vibrational assignments are reported with support by ab initio predictions and results are discussed.

Infrared and Raman spectra, ab initio calculations, conformational stability and vibrational assignment of 1-bromo-1-silacyclopentane.

Infrared and Raman spectra (3500-60 cm(-1)) of gas and/or liquid and solid 1-bromo-1-silacyclopentane (c-C4H8SiBrH) have been recorded and the vibrational data indicate the presence of a single conformer with no symmetry which is consistent with the twisted form. Ab initio calculations with a variety of basis sets up to MP2(full)/6-311+G(2df,2pd) predict the envelope-axial and envelope-equatorial conformers to be saddle points with nearly the same energies but approximately 900 cm(-1) (5.98 kJ/mol) lower in energy than the planar conformer. Density functional theory calculations by the B3LYP method predict slightly lower energies for the two envelope forms and considerably lower energy for the planar form compared to the MP2 predictions. By utilizing the MP2(full)/6-31G(d) calculations the force constants, frequencies, infrared intensities, band contours, Raman activities, and depolarization values have been obtained to support the vibrational assignment. Estimated r0 structural parameters have been obtained from adjusted MP2(full)/6-311+G(d,p) calculations. These experimental and theoretical results are compared to the corresponding quantities of some other five-membered rings.

Conformational stability, r0 structural parameters, and vibrational assignments of mono-substituted cyclobutanes: fluorocyclobutane.

Variable temperature (-55 to -100°C) studies of the infrared spectra (3500-400 cm(-1)) of fluorocyclobutane, c-C(4)H(7)F, dissolved in liquid xenon have been carried out as well as the infrared spectra of the gas. By utilizing eight pairs of conformers at 10 different temperatures, the enthalpy difference between the more stable equatorial conformer and the axial form has been determined to be 496±40 cm(-1) (5.93±0.48 kJ/mol). The percentage of the axial conformer present at ambient temperature is estimated to be 8±1%. The ab initio MP2(full) average predicted energy difference from a variety of basis sets is 732±47 cm(-1) (9.04±0.44 kJ/mol) and the average value of 602±20 cm(-1) from density functional theory predictions by the B3LYP method are significantly larger than the experimentally determined enthalpy value. By utilizing previously reported microwave rotational constants for the equatorial and axial conformers combined with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r(0) parameters have been obtained. The determined heavy atom structural parameters for the equatorial [axial] conformer are: distances (Å) C-F=1.383(3) [1.407(3)], C(α)-C(ß)=1.543(3) [1.546(3)], C(ß)-C(γ)=1.554(3) [1.554(3)] and angles (°) ∠C(α)C(ß)C(γ)=85.0(5) [89.2(5)], ∠C(ß)C(α)C(ß)=89.3(5) [89.2(5)], ∠F-(C(ß)C(α)C(ß))=117.4(5) [109.2(5)] and a puckering angle of 37.4(5) [20.7(5)]. The conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies have been obtained for both conformers from MP2(full)/6-31G(d) ab initio calculations and compared to experimental values where available. The results are discussed and compared to the corresponding properties of some other monosubstituted cyclobutanes with halogen and pseudo-halogen substituents.