Conformational stability from variable temperature infrared spectra of xenon solution, r0 structural parameters, and vibrational assignment of fluorocyclohexane

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 seen from the table, the DF's consistently predict the H Ax−Eq 's for the axial conformations to be lower than the other methods and lower than the accurate experimental measurements for the methyl, 5 fluoro, 6 and chloro 4 cyclohexanes in the gas phase and in xenon solutions when used with the D95** basis set. The PBE1PBE functional consistently give experimental enthalpy differences closest to the experimental reports.…”

“…We compared the performance normal and dispersion corrected functionals for the calculations of antiparallel β-sheets consisting of four strands of acetyl(Ala) 6 NHCH 3 . The calculations used both pure DFT methods and ONIOM where the high level is DFT and the low level AM1.…”

“…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.…”

Conformational stability, infrared and Raman spectra, vibrational assignments, and theoretical calculations of cyclohexylamine

“…The investigation of six-membered rings with non-substituted cyclohexane started in our laboratory by studying the relative intensities of the Raman active fundamentals and the potential function governing the conformational interchange between the chair and twisted boat form [3]. Studies were initiated to spectroscopically investigate monosubstituted chloro- [4], bromo- [5] and fluorocyclohexane [6] to further understand the conformational stability of the chair form, since there are only two conformers, equatorial and axial forms, which exist at ambient temperature. Due to the repulsive non-bonded nature of the interaction between the axial and the equatorial substituent, the equatorial conformation is generally favored according to two study reported previously [2,7] and these monosubstituted cyclohexanes exist mostly in the equatorial form.…”