Conformational stability from Raman spectra, r₀ structural parameters, and vibrational assignment of methylcyclohexane

Abstract

The Raman spectra (3500-50 cm −1 ) of the liquid and solid methylcyclohexane and the infrared spectra of the gas and solid methylcyclohexane have been recorded. The Raman band at 754 cm −1 in the liquid has been confidently assigned to the less stable axial conformer and its intensity was recorded as a function of temperature from 25 to −95 • C. By the utilization of 15 different temperatures, the enthalpy difference between the more stable chair-equatorial conformer and the chair-axial form was determined to be 712 ± 71 cm −1 (8.50 ± 0.84 kJ/mol). The ab initio predicted value of 710 cm −1 (8.50 kJ/mol) from the MP2(full)/6-311G(2d,2p) calculations with and without diffuse functions is in excellent agreement. The harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational wavenumbers have been obtained for both conformers from MP2(full)/6-31G(d) ab initio calculations. With two scaling factors of 0.88 for the C-H stretches and 0.9 for the remaining ones, the fundamental wavenumbers have been predicted and along with the depolarization values and infrared band contours (B-type for A modes) a complete vibrational assignment has been made for the chair-equatorial conformer. Predicted r 0 structural parameters have been provided from adjusted parameters from ab initio MP2(full)/6-311+G(d,p) calculations. The results are discussed and compared with the corresponding properties of some similar molecules. Copyright

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.…”

“…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.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part IV

“…Anyone interested in the exact methodology used is invited to view the abstract of the paper at the Journal website or to download and read the paper in its entirety. The molecules for which vibrational analysis has been carried out through the standard methods of quantum chemistry are: 4‐chloro‐ and 4‐bromophenylboronic acid,276 4‐( N , N ‐dimethylamino)‐ N ‐methyl‐4′‐toluene sulfonate,277 C 7 H 15 CONH 2 ‐ valpromide,278 L ‐arginine nitrate hemihydrate,279 Azure A chloride, 3‐amino‐7‐(dimethylamino) phenothiazin‐5‐ium chloride,280 8‐( n ‐butylaminophenylmethyliden)‐1,2,3,4,5,6,7‐heptathiocane which contains a CS7 ring,281 N ‐acetyl‐ L ‐Asp and N ‐acetyl‐ L ‐Glu in the solid state,282 N ‐acetyl‐ L ‐Asp‐ L ‐Glu in the solid state,283 7‐chloro‐3‐methyl‐2 H ‐1,2,4‐benzothiadiazine 1,1‐dioxide,284 strontium tartrate (C 4 H 4 O 6 Sr),285 flavonoid derivatives baicalein and naringenin,2863‐{[(4‐fluorophenyl)methylene]amino}‐2‐phenylquinazolin‐4(3 H )‐one,287 1‐benzyl‐1 H ‐imidazole,288 hydrated platinum(II), palladium(II) and cis ‐diammineplatinum(II) ions in acidic solution,289 ibuprofen‐cyclodextrin inclusion complexes,290 the anticancer drug combretastatin‐A2,291 the grossular garnet Ca 3 Al 2 Si 3 O 12 ,292 2‐fluoro‐6‐nitrotoluene,293 (CH 3 ) 3 GeBr,294 benzoic acid and 3,5‐dichloro salicylic acid,295 PCCMB 2,5 dimethyl‐1‐phenylpyrazolium‐3‐carboxylate and its isomer the CCMB 1,3‐dimethyl‐2‐phenylpyrazolium‐4 carboxylate,296 the nonpeptide antagonist irbesartan,297 3‐{[(2‐hydroxyphenyl)methylene]amino}‐2‐phenylquinazolin‐4(3 H )‐one,298 4‐chloro‐2‐(4‐bromophenylcarbamoyl)phenyl acetate,299 1,4,5‐triazanaphthalene,300 Martius yellow sodium salt monohydrate,301 1,3‐dibromo‐2,4,5,6‐tetrafluorobenzene and 1,2,3,4,5‐pentafluorobenzene,302 4‐hydroxy‐3[1‐(4‐nitrophenyl)‐3‐oxobutyl]‐2 H ‐1‐benzopyran‐2‐one, acenocoumarol sodium salt,303 N ‐(2′‐furyl)imidazole,304 N ‐hydroxyphthalimide,305 3,3,7,7‐tetrakis(difluoramino)octahydro 1,5‐dinitro‐1,5‐diazocine,306 p ‐bromonitrobenzene,307 4‐chloro‐2‐(3‐chlorophenylcarbamoyl)phenyl acetate,308 alkylamides of thiocyanoacetic acid,309 1,2‐bis(trifluorosilyl)ethane (SiF3CH2CH2SiF3),310 organomolybdenum dithiolene complexes Cp2Mo(dmit),311 methyl trifluoroacetate (CF3C(O)OCH3),312 nitrofurantoin polymorphs,313 methylcyclohexane,314 ethyl‐3‐(3, 4‐dihydroxyphenyl)‐2‐propenoate,315 anilinium sulfate,316 valpromide and some derivatives with antiepileptic activity,…”

Computational study of inversion‐topomerization pathways in 1,3‐dimethylcyclohexane and 1,4‐dimethylcyclohexane: Ab initio conformational analysis

“…With respect to this, the ongoing researches have been devoted to exploring the substituted cyclohexanes in terms of the determination of conformational preference, relative energies of various conformers, thermodynamic stability and equilibrium, axial/equatorial reversal and ratios, and interconversion mechanism. Durig et al [22] looked into the influence of mono‐substitution on cyclohexane, resulting in the formation of both equatorial and axial forms by Raman spectra and quantum chemical calculations. And they reported the conformational stabilities of MCH conformers regarding to r 0 structural parameters, vibrational assignment, and ab initio results.…”