Conformational stability of chlorocyclohexane from temperature-dependent FT-IR spectra of xenon solutions, r 0 structural parameters, and vibrational assignment

Abstract

Variable temperature (-55 to -105°C) studies of the infrared spectra (4000-400 cm -1 ) of chlorocyclohexane (c-C 6 H 11 Cl) dissolved in liquefied xenon have been carried out. The infrared spectra of the gas and solid have also been recorded from 4000-100 cm -1 . By analyzing six conformer pairs in the xenon solution, a standard enthalpy difference of 132 ± 13 cm -1 (1.58 ± 0.16 kJ/mol) was obtained with the equatorial conformer the more stable form. At ambient temperature, the abundance of the axial conformer is 34 ± 1%. The potential surface describing the conformational interchange has been determined and the Fourier coefficients were obtained. From MP2 ab initio calculations utilizing various basis sets with and without diffuse functions, the equatorial conformer is predicted to be more stable by 161 ± 18 cm -1 from the four largest basis set calculations, which is consistent with the experimental results. However, the average from the corresponding B3LYP density functional theory calculations is 274 ± 15 cm -1 which is certainly too large. By utilizing the previously reported microwave rotational constants for two isotopomers ( 35 Cl, 37 Cl) combined with the structural parameters predicted from the MP2(full)/6-311+G(d,p) calculations, adjusted r 0 structural parameters have been obtained. The determined heavy atom distances for the most stable chairequatorial conformer in Å are: r 0 (C 1 -C 7 , 8 ) = 1.532(3); r 0 (C 7 , 8 -C 13 , 14 ) = 1.536(3); r 0 (C 4 -C 13 , 14 ) = 1.524(3); and r 0 (C 4 -Cl 6 ) = 1.802(5) and the angles in degrees: \C 1 C 7 , 8 C 13 , 14 = 111.3(5)8; \Cl 6 C 4 C 13 , 14 = 109.7(5)8 with the two dihedral angles \C 8 C 1 C 7 C 13 = 56.3(10)8 and \C 14 C 4 C 13 C 7 = 56.7(10)8. These parameters are in good agreement with those reported earlier from microwave and electron diffraction studies where the CC and CH distances were all assumed to be equal. A few of the previously reported vibrational assignments have been corrected. The results of these spectroscopic and theoretical studies are discussed and compared to the corresponding results for some similar molecules.

Comparison of some dispersion-corrected and traditional functionals as applied to peptides and conformations of cyclohexane derivatives

“…Clearly, noncovalent interactions occur between solutes and solvents as well as between the substituents and the axial H's (when the substituent is in the axial position). The same reports [4][5][6] contain MP2 calculations using basis sets as large as 6-311+G(2p,2d) which are in reasonable agreement with the experimental observations. Our results show that these H's increase upon improving the basis set from d95** to aug-cc-pVTZ for all functionals except M06 and M06L.…”

“…As a complementary test to this study, we examine the relative energies of axial and equatorial conformations of some substituted cyclohexanes for which precise H's in the gas phase or noninteracting media have been recently reported. [4][5][6] The steric a) jdannenberg@gc.cuny.edu.…”

Contrasting organic aerosol particles from boreal and tropical forests during HUMPPA-COPEC-2010 and AMAZE-08 using coherent vibrational spectroscopy

“…We conclude from these results that the SFG spectrum of (+)-α-pinene exhibits just the asymmetric and symmetric methyl CH stretches at 2960 cm −1 and 2880 cm −1 as well as a methyl Fermi resonance at 2940 cm −1 , which dominates the spectral response. In α-and β-pinene, the methylene asymmetric stretch of the CH 2 on the four-membered ring may be shifted to higher frequencies (2950-2990 cm −1 ) due to ring strain, and contribute to the signal observed in this range (Galabov et al, 1972;Durig et al, 1990Durig et al, , 2008Ball, 1997;Buchbinder et al, 2010a).…”

FTIR investigation of molecular mobility in glassy epoxy-amine oligomers with azo-chromophores

“…The absorption bands at 709 cm -1 Q(CCl) (t-conformation), 653 cm -1 Q(CCl) (g-conformation) [8] of DCE and 684 cm -1 Q(CCl) (a-conformation), 888 cm -1 Q(CC) (e-conformation) [9] of CCH were chosen as analytical bands. These absorption bands fall within the "transparency windows" of CFAO.…”