Solvent effects on 2-methoxyethanol conformers: an ab initio DFT study using the SCI-PCModel (original) (raw)
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Journal of Molecular Structure, 1999
The IR (4000-400 cm Ϫ1) and Raman (4000-50 cm Ϫ1) spectra of 3-methoxymethylene-2,4-pentanedione (H 3 CO -CHyC (COCH 3) 2) in the liquid and solute forms in various solvents of different polarity were recorded at ambient temperature. Additional IR and Raman spectra were obtained for amorphous and crystalline solid at low temperature. The vibrational spectra revealed that compound exists atleast in two dominant conformers with different polarity and that conformer present in the solid phase is less polar. NMR spectra in various solvents at different temperatures were also obtained.The compound can exist in several conformers as a result of rotation around O-Cy and both yC-C bonds with planar or nonplanar arrangement of the heavy atoms. Semiempirical (AM1, PM3, MNDO, MINDO3) and ab initio using TZP and 6-31G** basis sets calculations were carried out. According to ab initio calculations at least five conformational structures with the methoxy group oriented as anti or syn and carbonyl groups oriented as Z or E towards the CyC double bond were obtained at energy surface. The calculated ab initio and AM1 energies of all conformers suggest as the most stable anti-ZE conformer where Z and E regard of the trans and cis acetyl group, respectively. As the second most stable conformer with energy at least 10 kJ mol Ϫ1 higher was calculated anti-EZ conformer. Assignments of the vibrational spectra for the studied compound were made with the aid of normal coordinate calculations employing scaled ab initio force field constants. The scaled ab initio frequencies as well as calculated energies indicate that the conformer present in the solid phase is anti-ZE.
Journal of Physical Organic Chemistry, 2002
The conformational equilibria of trans-1-methoxy-2-chloro-(1), trans-1-methoxy-2-bromo-(2) and trans-1-methoxy-2-iodocyclohexane (3), and their corresponding alcohols (4-6), were studied through a combined method of NMR, theoretical calculations and solvation theory. They can be described in terms of the axial-axial and equatorial-equatorial conformations, taking into account the main rotamers of each of these conformations. From the NMR experiments at 183 K in CD 2 Cl 2-CS 2 , it was possible to observe proton H 2 in the ax-ax and eq-eq conformers separately for 1 and 2, but not for 3, which gave directly their populations and conformer energies. In the alcohols the proportion of the ax-ax conformer was too low to be detected by NMR under these conditions. Those HH couplings together with the values at room temperature, in a variety of solvents allowed the determination of the solvent dependence of the conformer energies and hence the vapor state energy difference. The DE (E axE eq) values in the vapor state for 1, 2 and 3 are À0.05, 0.20 and 0.55 kcal mol À1 , respectively, increasing to 1.10, 1.22 and 1.41 kcal mol À1 in CD 3 CN solution (1 kcal = 4.184 kJ). For 4-6 the eq-eq conformation is always much more stable in both non-polar and polar solvents, with energy differences ranging from 1.78, 1.94 and 1.86 kcal mol À1 (in CCl 4) to 1.27, 1.49 and 1.54 kcal mol À1 (in DMSO), respectively. Comparison of the hydroxy and methoxy compounds gives the intramolecular hydrogen bonding energy for the alcohols as 1.40, 1.36 and 1.00 kcal mol À1 (in CCl 4) for 4, 5 and 6, respectively.
Solvent Effects on Molecular Structure, Vibrational Frequencies, and NLO Properties of N-(2,3-Dichlorophenyl) -2-Nitrobenzene–Sulfonamide: a Density Functional Theory Study, 2016
Density functional theory (DFT) calculations have been performed to obtain optimized geometries, vibrational wavenumbers, highest occupied molecular orbital (HOMO)lowest unoccupied molecular orbital (LUMO) energies, nonlinear optical (NLO), and thermodynamic properties as well as molecular surfaces for N-(2,3-dichlorophenyl)-2-nitrobenzene-sulfonamide in different solvents. B3LYP level gives similar results for geometric parameters and vibration frequencies in gas phase, water, and ethanol solvents. The most stable structure, which is defined by the highest energy gap between H O M O a n d L U M O , i s o b t a i n e d i n g a s p h a s e (ΔE = 10.7376 eV). Obtained small energy gaps between HOMO and LUMO demonstrate the high-charge mobility in the titled compound. The magnitude of first static hyperpolarizability (β) parameter increases by the decreasing HOMO-LUMO energy gap. The intensive interactions between bonding and antibonding orbitals of titled compound are responsible for movement of π-electron cloud from donor to acceptor, i.e., intramolecular charge transfer (ICT), inducing the nonlinear optical properties. So, the β parameter for title compound is found to be in the range of 5.5255-3.7187 × 10 −30 esu, indicating the considerable NLO character. All of these calculations have been performed in gas phase as well as water and ethanol solvents in order to demonstrate solvent effect on molecular structure, vibration frequencies, NLO properties, etc.
The Raman and infrared spectra of solid methyl-5-amino-4-cyano-3-(methylthio)-1H-pyrazole-1- carbodithioate (MAMPC, C7H8N4S3) were measured in the spectral range of 3700–100 cm−1 and 4000–200 cm−1 with a resolution of 4 and 0.5 cm−1, respectively. Room temperature 13C NMR and 1H NMR spectra from room temperature down to −60 ◦C were also recorded. As a result of internal rotation around C–N and/or C–S bonds, eighteen rotational isomers are suggested for the MAMPC molecule (Cs symmetry). DFT/B3LYP and MP2 calculations were carried out up to 6-311++G(d,p) basis sets to include polarization and diffusion functions. The results favor conformer 1 in the solid (experimentally) and gaseous (theoretically) phases. For conformer 1, the two –CH3 groups are directed towards the nitrogen atoms (pyrazole ring) and C S, while the –NH2 group retains sp2 hybridization and C–C N bond is quasi linear. To support NMR spectral assignments, chemical shifts (ı) were predicted at the B3LYP/6- 311+G(2d,p) level using the method of Gauge-Invariant Atomic Orbital (GIAO) method. Moreover, the solvent effect was included via the Polarizable Continuum Model (PCM). Additionally, both infrared and Raman spectra were predicted using B3LYP/6-31G(d) calculations. The recorded vibrational, 1H and 13C NMR spectral data favors conformer 1 in both the solid phase and in solution. Aided by normal coordinate analysis and potential energy distributions, confident vibrational assignments for observed bands have been proposed. Moreover, the CH3 barriers to internal rotations were investigated. The results are discussed herein are compared with similar molecules whenever appropriate.
Journal of Physical Chemistry A, 1997
The global conformational potentials of 1,2-ethanediol, 1,2-ethanediamine, and 2-aminoethanol (X-CH 2-CH 2-Y; X, Y) OH or NH 2) were obtained at the MP2/6-311+G(2d,p) level by scanning through the dihedral angles of the two functional groups and the carbon-carbon bond with the remaining nuclear coordinates being energy-minimized. It was found that the potentials could be represented by the direct-bond potentials between the adjacent molecular fragments and by the through-space electrostatic potentials between the vicinal and geminal fragments. Here, the through-direct-bond potentials are represented by the conventional three Fourier terms of the internal rotation angles, and the through-space potentials, which include the intramolecular hydrogen bonding between X and Y, are represented by the general functional forms of the electric dipoledipole, dipole-quadrupole, and quadrupole-quadrupole interaction terms. The fitted electrostatic interaction strengths between the X and Y fragments are in good agreement with the predictions of the theoretical molecular fragment dipole and quadrupole moments calculated by the Hirshfeld charge population analysis. Under the present energy decomposition scheme, the intrinsic gauche interactions, which are free of the contribution of the intramolecular H-bonding, could be obtained and correlated with the group electronegativities of X and Y. The potentials were also calculated by the MM3 molecular mechanics method and compared with the present results. With the global conformation potentials, the thermodynamic functions of the molecules and also their individual conformers are calculated and compared with the gas-phase experimental thermodynamic data in the literature.
Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2007
The Raman (3700-100 cm −1 ) and infrared (4000-400 cm −1 ) spectra of solid 2-aminophenol (2AP) have been recorded. The internal rotation of both OH and NH 2 moieties produce ten conformers with either C s or C 1 symmetry. However, the calculated energies as well as the imaginary vibrational frequencies reduce rotational isomerism to five isomers. The molecular geometry has been optimized without any constraints using RHF, MP2 and B3LYP levels of theory at 6-31G(d), 6-311+G(d) and 6-31++G(d,p) basis sets. All calculations predict 1 (cis; OH is directed towards NH 2 ) to be the most stable conformation except RHF/6-31++G(d,p) basis set. The 1 (cis) isomer is found to be more stable than 8 (trans; OH is away from the NH 2 moiety and the NH bonds are out-of-plane) by 1.7 kcal/mol (598 cm −1 ) as obtained from MP2/6-31G(d) calculations. Aided by experimental and theoretical vibrational spectra, cis and trans 2AP are coexist in solution but cis isomer is more likely present in the crystalline state. Aided by MP2 and B3LYP frequency calculations, molecular force fields, simulated vibrational spectra utilizing 6-31G(d) basis set as well as normal coordinate analysis, complete vibrational assignments for HOC 6 H 4 NH 2 and DOC 6 H 4 ND 2 have been proposed. Furthermore, we carried out potential surface scan, to determine the barriers to internal rotations of NH 2 and OH groups. All results are reported herein and compared with similar molecules when appropriate.
The Journal of Organic Chemistry, 2011
Conformational problems often involve very small energy differences, even low as 0.5 kcal mol -1 . This accuracy can be achieved by theoretical methods in the gas phase with the appropriate accounting of electron correlation. The solution behavior, on the other hand, comprises a much greater challenge. In this study, we conduct and analysis for cis-2-fluoro-, cis-2-chloro-, and cis-2bromocyclohexanol using low temperature NMR experiments and theoretical calculations (DFT, perturbation theory, and classical molecular dynamics simulations). In the experimental part, the conformers' populations were measured at 193 K in CD 2 Cl 2 , acetone-d 6 , and methanol-d 4 solutions; the preferred conformer has the hydroxyl group in the equatorial and the halogen in the axial position (ea), and its population stays at about 60-70%, no matter the solvent or the halogen. Theoretical calculations, on the other hand, put the ae conformer at a lower energy in the gas phase (MP2/ 6-311þþG(3df,2p)). Moreover, the theoretical calculations predict a markedly increase in the conformational energy on going from fluorine to bromine, which is not observed experimentally. The solvation models IEF-PCM and C-PCM were tested with two different approaches for defining the atomic radii used to build the molecular cavity, from which it was found that only with explicit consideration of hydrogens can the conformational preference be properly described. Molecular dynamic simulations in combination with ab initio calculations showed that the ea conformer is slightly favored by hydrogen bonding.
Journal of Molecular Structure, 1999
The IR (4000-400 cm Ϫ1) and Raman (4000-50 cm Ϫ1) spectra of 3-methoxymethylene-2,4-pentanedione (H 3 CO -CHyC (COCH 3) 2) in the liquid and solute forms in various solvents of different polarity were recorded at ambient temperature. Additional IR and Raman spectra were obtained for amorphous and crystalline solid at low temperature. The vibrational spectra revealed that compound exists atleast in two dominant conformers with different polarity and that conformer present in the solid phase is less polar. NMR spectra in various solvents at different temperatures were also obtained.The compound can exist in several conformers as a result of rotation around O-Cy and both yC-C bonds with planar or nonplanar arrangement of the heavy atoms. Semiempirical (AM1, PM3, MNDO, MINDO3) and ab initio using TZP and 6-31G** basis sets calculations were carried out. According to ab initio calculations at least five conformational structures with the methoxy group oriented as anti or syn and carbonyl groups oriented as Z or E towards the CyC double bond were obtained at energy surface. The calculated ab initio and AM1 energies of all conformers suggest as the most stable anti-ZE conformer where Z and E regard of the trans and cis acetyl group, respectively. As the second most stable conformer with energy at least 10 kJ mol Ϫ1 higher was calculated anti-EZ conformer. Assignments of the vibrational spectra for the studied compound were made with the aid of normal coordinate calculations employing scaled ab initio force field constants. The scaled ab initio frequencies as well as calculated energies indicate that the conformer present in the solid phase is anti-ZE.
The impacts of the endo-and exo-anomeric effects (endo-AE and exo-AE), electrostatic interactions and steric repulsions on the conformational behaviors of 2-fluoro-1,3-dioxane, -dithiane, -diselenane (1-3), 2-chloro-1,3-dioxane, -dithiane, -diselenane (4-6) and 2-bromo-1,3-dioxane, -dithiane, -diselenane (7-9) have been analyzed by means of natural bond orbital (NBO) interpretation, hybrid density functional theory (B3LYP/6-311+G**) and ab initio molecular orbital (HF/6-311+G**) based methods. Both methods showed the axial preference for compounds 1-9. The calculated Gibbs free energy difference (Geq-Gax) values (i.e. ∆Geq-ax) between the axial and equatorial conformations increases from compound 1 to compound 2 but decreases from compound 2 to compound 3. Contrary to trend observed for compounds 1-3, the calculated ∆Geq-ax values decrease from compound 4 to compound 6 and from compound 7 to compound 9. Similar trends were also observed for the corresponding calculated AE values. On the other hand, the calculated differences between the dipole moment values of the axial and equatorial conformations, ∆(μ eq -μ ax ), can not explain the variation of the calculated ∆G eq-ax for compounds 1-9. Consequently, the electrostatic model fails to account for the axial preferences in compounds 1-9. There is a conflict between the AE associated with electron delocalization and the steric effect impacts on the conformational behavior of compounds 1-9.