Conformational analysis of 1,2-dichloroethane adsorbed in metal-organic frameworks

This paper describes the conformational analysis of 1,2-dichloroethane adsorbed into three different metal-organic frameworks, MIL-53(Al), MIL-68(In), MIL-53-NH₂(Al), by using FT-Raman spectroscopy in combination with powder XRD and TGA. For non-polar frameworks, the main guest-host interactions are van der Waal interactions between the CH bonds of 1,2-dichloroethane (DCE) and the π system of terephthalate ligands. The polar framework of MIL-53-NH₂ is able to stabilize the gauche conformation of DCE at room temperature. The conformational enthalpy of each system was determined through variable temperature FT-Raman spectroscopy. Furthermore, the line-width of the Raman bands provides information regarding the molecular motion of the halocarbons at various temperatures inside the framework.     

Conformational equilibrium of 1,2-dichloroethane in water: comparison of PCM and RISM-SCF methods

The RISM-SCF and polarizable continuum model (PCM) approaches have been applied to study the conformational equilibrium of 1,2-dichloroethane (DCE) in water. Both the electron correlation effect and basis sets play an important role in the relative energies of the gauche and trans conformers in gas and solution phases. Both PCM and RISM-MP2 methods resulted in a consistent trend with the previous experimental and theoretical studies that the population of the gauche conformer increases in going from the gas phase to the aqueous solution. However, the PCM treatment could not describe the solvent effect completely in that the sign of the relative free energy of the gauche and trans forms is opposite to the most recent experimental and theoretical data, while the RISM-MP2 gives the right sign in the free energy difference. We found that the larger excess chemical potential gain (by ca. -4.1 kcal/mol) for the gauche conformer is large enough to result in the gauche preference of DCE in water, though it has to compensate for more solute reorganization energy (approximately 1.6 kcal/mol) and overcome the energy difference (approximately 1.6 kcal/mol) in the gas phase. The radial distribution functions between DCE and the nearest water shows that the electrostatic repulsion between chlorine and oxygen atoms is higher in the trans conformer than in the gauche one, while the attractive interaction between chlorine and hydrogen of water is higher in the gauche conformer.     

Acid-base strengths in 1,2-dichloroethane

The pK_a value of hydriodic acid in 1,2-dichloroethane was determined from conductivity measurements. A glass electrode was calibrated for dichloroethane in the potentiometric titration of hydriodic acid with tetramethylguanidine. From potentiometric titrations, the pK_a values in dichloroethane of hydrobromic acid, hydrochloric acid, picric acid and some sulfonphthaleins as well as some protonated nitrogen bases were determined. In the curves of the titrations of the carboxylic acids and the hydrogen halides with TMG, evidence was found for the formation of the complex B(HX)₂.     

Conformational analysis. Part 16 Conformational free energies in substituted piperidines and piperidinium salts

Summary The conformational free energies (-G^o) of a number of 4-substituted piperidines and piperidinium salts have been determined by the J-value method. For the 4-substituted piperidines (R=Me, Phenyl, CO₂Et, Br, OH, F) the relative conformer energies are almost identical to those of the analogous cyclohexanes.The methyl and phenyl compounds showed no change in the couplings on protonation, implying no change in the conformer energies. In constrast, in the remaining compounds with polar 4-substituents an almost constant stabilisation of the axial conformer of ca. 0.7–0.8 kcal mol^-1 was observed on protonation. In three cases (R=F, OH and Br) the conformational preferences is reversed on protonation and the axial form is favoured.The conformer energies of both the free bases and the piperidinium salts can be quantitatively predicted by molecular mechanics calculations using the COSMIC force-field, in which the electrostatic interactions are calculated by a simple Coulombic model with the partial atomic charges in the molecules given by the CHARGE2 routine, and an effective dielectric constant of five. The precise agreement obtained demonstrates conclusively that the electrostatic interactions between the substituents and the protonated nitrogen are the cause of the conformational changes on protonation, and that these can be modelled successfully using existing force-fields.For Part 15, see Ref. 1.     

Conformational energies of cyclenes

An universal function for non-bonded interactions, which takes into account the relative orientation of the bonds is considered in calculating the conformational energies of cycloalkenes and cycloalkadienes. A comparison is made with previous results obtained by using usual 6-exp functions for non-bonded interactions.     

Molar heat capacity of binary liquid mixtures: 1,2-dichloroethane + cyclohexane and 1,2-dichloroethane + methylcyclohexane

The molar heat capacity at constant pressure, C_P, of the two binary liquid mixtures 1,2-dichloroethane + cyclohexane and 1,2-dichloroethane + methylcyclohexane were determined at 298.15 K from measurements of the volumetric heat capacity, C_P/V, in a Picker flow microcalorimeter (V is the molar volume). For the molar excess heat capacity, C_P^E, the imprecision of the adopted stepwise procedure is characterized by a standard deviation of about ± 0.05 J K^?1 mole^?1, which amounts to ca. 3% of C_P^E. Literature data on ultrasonic velocities, on molar volumes, and on coefficients of thermal expansion were used to calculate the molar heat capacity at constant volume, C_v, and the isothermal compressibility, β_T, of the pure substances, as well as the corresponding excess quantities C_V^E and (Vβ_T)^E of the binary mixture 1,2-dichloroethane + cyclohexane. A preliminary discussion of our results in terms of external and internal rotational behavior (trans-gauche equilibrium of 1,2-dichloroethane) is presented.     

Calculations of pKa of superacids in 1,2-dichloroethane

Acidity calculations for some CH and NH superacids in 1,2-dichloroethane (DCE) were carried out using SMD and COSMO-RS continuum solvation models. After comparing the results of calculations with respective experimental pK(a) values it was found that the performance of SMD/M05-2X/6-31G* method is characterized by the mean unsigned error (MUE) of 0.5 pK(a) units and the slope of regression line of 0.915. The similar SMD/B3LYP/6-31G* approach was slightly less successful. The strong correlation over entire data set is confirmed by R(2) values of 0.990 and 0.984 for M05-2X and B3LYP functionals, respectively. The COSMO-RS method, while providing the value of the linear regression line slope similar to the corresponding values from SMD approach, characterized by rather loose correlation (R(2) = 0.823, MUE = 1.7 pK(a) units) between calculated and experimental pK(a) values in DCE solution.     

Thermal behaviour of resorcinol-1,2-dichloroethane resin

Resorcinol-1,2-dichloroethane resin was prepared by Friedel-Craft polymerization from resorcinol and 1,2-dichloroethane. The resin sample was characterised by IR and UV spectra and the average molecular weight was determined by vapour pressure osmometry. Kinetic parameters from TG and DTA thermograms are reported.     

Conformational energies of aromatic polyamides

PCILO conformational calculations have been made on several model compounds of aromatic polyamides. The calculated structures can be compared with the X-Ray crystallographic analyses and related to the physical properties of these polymers. Poly-p-phenylene terephthalamide appears as a more flexible polymer than poly-p-benzamide.     

Phase-Transfer catalyzed alkylation of morpholine with 1,2-dichloroethane

Russian Journal of General Chemistry -     

Modification of the catalyst surface in 1,2-dichloroethane decomposition

The strong and irreversible chemisorption of substrate or (and) reaction products (self-poisoning of catalyst surface) has been found to account for an activity decrease and changes in catalytic selectivity in the reaction. The mechanism of 1,2-dichloroethane (1,2-DCE) decomposition has been discussed.

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1,2- (1,2-), , . , — — () («» ) . 1,2-.

     

Chiral separation of amines with N-benzoxycarbonylglycyl-L-proline as selector in non-aqueous capillary electrophoresis using methanol and 1,2-dichloroethane in the background electrolyte

N-Benzoxycarbonylglycyl-L-proline (L-ZGP) has been introduced as a chiral selector for enantioseparation of amines in non-aqueous capillary electrophoresis. Methanol mixed with different proportions of dichloromethane, 1,2-dichloroethane or 2-propanol containing L-ZGP and ammonium acetate was used as the background electrolyte. Enantioseparation of different types of pharmacologically active amines was performed, e.g. the local anaesthetic bupivacaine and the beta-adrenoceptor blocking agent pindolol. Addition of the solvents (dichloromethane, 1,2-dichloroethane or 2-propanol) gave an improved chiral separation partly due to a distinct decrease in the electroosmotic flow. The use of 1,2-dichloroethane in the background electrolyte gave higher precision in migration time (RSD 2.2%) compared to the systems containing dichloromethane. An enantiomeric separation of mepivacaine was performed within 72 s by use of short-end injection with an effective capillary length of 8.5 cm.     

Conformational energies and hydrogen bonding in dichloroethanol

The conformational energy differences have been measured for 2,2-dichloroethanol in the neat liquid and in DMSO and H2O via Raman spectroscopy. In contrast to earlier results on 2-chloroethanol, ΔH was not markedly effected by dilution in these hydrogen bonding solvents. Spectra in the OH valence region were utilized to determine the energy difference between intra- and intermolecularly hydrogen bonded species. The result indicated stronger intramolecular hydrogen bond formation in dichloroethanol than in the monohalogenated alcohol.     

Proton transfer in nanoconfined polar solvents. 1. Free energies and solute position

The reaction free energy curves for a model phenol-amine proton-transfer system in a confined CH3Cl solvent have been calculated by Monte Carlo simulations. The free energy curves, as a function of a collective solvent coordinate, have been obtained for several fixed reaction complex radial positions (based on the center-of-mass). A smooth, hydrophobic spherical cavity was used to confine the solvent, and radii of 10 and 15 A have been considered. Quantum effects associated with the transferring proton have been included by adding the proton zero-point energy to the classical free energy. The results indicate the reaction complex position can be an important component of the reaction coordinate for proton-transfer reactions in nanoconfined solvents.     

Conformational study of 1,2-dithiacyclononane

The temperature dependence of the Raman spectrum of 1,2-dithiacyclononane (1,2-DTCN) in the SS stretching region has been used to infer the existence of a conformational equilibrium with ΔH⁰ = 5.0 ± 0.8 kJ/mol. Molecular mechanics calculations predict a (2 2 5)-C₂ lowest energy conformation in equilibrium with a (2 3 4) structure. The fully decoupled ¹³C NMR spectrum at −80°C and the Raman spectra are consistent with this postulate. The temperature dependence of the ¹H NMR spectrum of 1,2-DTCN is characteristic of the ring inversion process. A crude lineshape analysis allows us to calculate ΔG⁰ = 49.0 ± 1.2 kJ/mol.     

Conformational energies for 2-substituted butanes

The conformational free energies for some 2-substituted butanes where X = F, Cl, CN, and CCH were calculated using G3-B3, CBS-QB3, and CCSD(T)/6-311++G(2d,p) as well as other theoretical levels. The above methods gave consistent results with free energies relative to the trans conformers as follows: X = CCH, g+ = 0.77 +/- 0.05 kcal/mol. g- = 0.88 +/- 0.05 kcal/mol; X = CN, g+ = 0.85 +/- 0.05 kcal/mol, g- = 0.75 +/- 0.05 kcal/mol; X = Cl, g+ = 0.70 +/- 0.05 kcal/ml, g- = 0.80 +/- 0.05 kcal/mol; and X = F, g+ = 0.53 +/- 0.05 kcal/mol, g- = 0.83 +/- 0.05 kcal/mol. The conformational free energies also were estimated using the observed liquid phase IR spectra and intensities calculated using B3LYP/6-311++G** and MP2/6-311++G**. The rotational free energy profiles for all of the compounds were estimated at the G3-B3 level.