Conformational properties of ethanediol in aqueous solution as described by the continuous model of the solvent (original) (raw)
Related papers
1986
Conformational energies of a small set of double rotor molecules (CH,CH,OH, CH,CHFOH(S), CH,FCH,OH, NH,CH,OH, CH,CH,OF) computed in vacua and in aqueous solution with three basis sets (STO-3G, 3-21G, 4-31G) are compared in order to examine the basis set dependence of the results. Solvent effects are introduced with an SCF algorithm which relies on a continuum description of the solvent. The interaction operator depends on the description of the solute charge distribution and, consequently, on the basis set employed in the calculations. 0166-1280/86/$03.50 o 1986 Elsevier Science Publishers B.V.
Journal of Physical Organic Chemistry, 1997
Ab initio optimizations at the HF/6-31G level and single-point calculations at the MP2/6-31G**//6-31G level were performed on ethane-1,1-diol and ethane-1,1,2-triol. Their conformational properties are discussed in terms of the anomeric effect, gauche effect and internal O-H interactions. The results showed a parallel behaviour with ethane-1,2-diol. The solvent effect was taken into account using the SCRF theory with a general cavity shape which is defined by the molecular surface.
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.
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.
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.
Solvent effects on 2-methoxyethanol conformers: an ab initio DFT study using the SCI-PCModel
Journal of Molecular Structure, 1999
The four stable conformers of 2-methoxyethanol, CH 3 O-CH 2 -CH 2 -OH (tgg H , ggg H , ttg and ttt) are studied by ab initio calculations using the SCRF theory and the SCI-PCModel to assess solvent effects on the structure and vibrational spectra of this compound. Full geometry optimizations were carried out at the B3LYP/6-311ϩG(3df,2df,2p)//B3LYP/6-31G(d) level, and normal mode calculations were performed within the harmonic approximation using the B3LYP/6-31G(d) derived force fields. The solvent, herein represented by a polarizable continuum with a defined dielectric constant, is found to affect significantly the geometry and dipole moment of the individual solute conformers. In addition, the results seem to suggest that the intramolecular H-bond type of interactions, which occur for tgg H and ggg H , tend to attenuate the solvent influence. In turn, the conformers which do not exhibit intramolecular H-bond interactions, ttg and ttt, exhibit a stronger solvent influence as revealed mainly by structural and electrostatic changes affecting both the ether O atom and the hydroxyl group. ᭧ Journal of Molecular Structure 482-483 (1999) 621-625 0022-2860/99/$ -see front matter ᭧
The Journal of Physical Chemistry B, 2018
The central OCCO backbone of the 1,2-ethanediol molecule adopts the gauche conformer in the gaseous and crystalline states but exists in conformational equilibrium between gauche and trans in the liquid; an observation that has been attributed to the competition between intra-and intermolecular interactions. Here we show that Nuclear Overhauser Effect (NOE) has the ability to distinguish inter-from intramolecular interactions in liquid 1,2-ethanediol. We do so by exploiting the secondary isotope effect to distinguish the hydroxyl protons of HOCH2CH2OH and the deuterated HOCD2CD2OH in the 1 H NMR spectra of mixtures of the two and, in conjunction with ab initio MD simulations show how the interplay between inter-and intramolecular interactions gives rise to the conformational isomers in the liquid state of 1,2-ethanediol.
Conformational Analyses of Glycinal and Alaninal: A Computational Study
Structural …, 2001
We present computational results from detailed gas-phase conformational analyses of the a-substituted aldehydes, glycinal and alaninal. A synplanar conformer of glycinal and a synperiplanar conformer of alaninal in which the C O and C a − N bonds are in an eclipsing orientation are found to be lowest in energy; the two amino hydrogen atoms in these conformers are both directed over the C a − C bond, i.e., in a compact arrangement. For the Group VA analogs, H 2 P − CH 2 − CHO and H 2 P − CH(CH 3 ) − CHO, skew conformers in which the C a − H and C a − Me groups, respectively, are in an eclipsing orientation with the C O bond are found to be lower in energy than the syn(peri)planar conformers. The results of various self-consistent reaction-field calculations suggest that the lowest-energy conformer of glycinal in 1, 2-dichloroethane is still synperiplanar, although the orientation of the amino hydrogen atoms may be different from that in the gas phase. Similar reaction-field calculations for alaninal raise the possibility that in this solvent a skew conformer, in which the C a − H bond is nearly eclipsing the C O bond, is energetically competitive with synperiplanar conformers.
Conformational equilibria of α-substituted carbonyl compounds. Study of solvent effects
Journal of Molecular Structure: THEOCHEM, 1993
PM3 computations have been performed to study conformational equilibria of a series of a-substituted carbonyl compounds in solution. The solvent is taken into account in the calculations by using cavity models. The compounds studied are a series of substituted acetaldehydes CH,R-CHO and cyclohexanones C,H,OR (R = F, Cl, Br, CN, NO,). The predicted solvent effects are in agreement with available experimental data. The discussion emphasizes the role played by the multipole moments and the necessity of going beyond the ellipsoidal cavity shape approximation in the case of substituted cyclohexanones.
The Journal of Physical Chemistry A, 2003
This work presents the determination of a semiclassical conformational partition function for bioactive compounds. The proposed partition function includes the effect of the rotovibrational coupling and the conformational kinetic energy, through the rotovibrational G matrix. In addition, the model considers a relaxed potential that includes the effect of the nonconformational, internal, coordinates. Comparison of results from harmonic and anharmonic vibrational models shows that the present partition function is a good approximation to the quantum one. The effect of the rotovibrational coupling and conformational kinetic energy, i.e. the G matrix, on the partition function is analyzed considering the biologically active, protonated, forms of nicotine and the nicotinic analgesic ABT-594. All energetic and structural data are derived from ab initio results at the MP2/cc-pVDZ level. Only two conformers are found to be significantly populated at physiological temperature in the nicotine case. The relative population of both conformers is clearly affected by the value of the G matrix. For ABT-594, several minima on the conformational potential energy hypersurface are found. However, only one conformer collects the population. Here, the distribution of population is only slightly affected by the G matrix. Performing simulations with a double minima potential, we show that for conformers separated by energy differences about or higher than 2 kcal mol-1 , the effect of the G matrix can be neglected.