Methanol pair interaction energies

The optimum UNIQUAC interaction parameters u, between methylcyclohexane, methanol, and ethylbenzene were determined using the observed liquid-liquid data, where the interaction parameters describe the interaction energy between molecules i and j or between each pair of compounds. Table 4 show the calculated value of the UNIQUAC binary interaction parameters for the mixture methanol + ethylbenzene using universal values for the UNIQUAC structural parameters. The equilibrium model was optimized using an objective function, which was developed by Sorensen [15],... 

Two methanol molecules initially adsorb with an interaction energy of 65 kJ/mol per molecule (i.e., 130 kJ/mol in total). This value is reassuringly lower than the value found by the same authors for adsorption of a single molecule (73 kJ/mol) (221). The adsorption is followed by a rotation of one of the methyl groups of methanol (the one on the right in Fig. 14) to enable interaction with the hydroxyl group of the other methanol. Calculation of reaction rate constants (245) shows that at reasonable temperatures for DME formation (400 K), for every 7 million pairs of methanol molecules that exist in the as-adsorbed state (PH-adsl in Fig. 14), only one pair exists in the rotated state. The transition state that subsequently leads to formation of adsorbed DME and water exhibits little strain on the SN2-like species ... 

The empirical determination of potential parameters has usually been performed assuming pairwise additivity for the molecular interactions, that is, that the total interaction energy is a summation of the interactions over all pairs of molecules. However, for many fluids such as water, methanol, and other highly polar molecules, pairwise additivity does not properly describe molecular interactions, especially in dense phases. This is why an approximate potential with one set of empirically adjusted or effective parameters cannot be made to reproduce a wide range of experimental data. Until recently, most simulations used the assumption of pairwise additivity. 

Fig. 3. Histogram of the pair-wise energy interaction between methanol and water (a) CH30H- OH2 isomer and (b) CH3HO- H2O isomer.

When methanol interacts with other molecules, there are some characteristic differences to water [36]. For example, methanol can symmetrically bind two HC1 molecules to its lone pairs without significant energy penalty compared to a cooperative ring arrangement [61]. This is not the case for water, because its... 

Coates and Jordan, 1960 Herskovits et cU., 1961) suggest that the phosphate groups of the DNA molecule are extensively paired to counterions in methanol solution, such that a /D (Section IV,B,1) is only roughly one-sixth of its value in water. This applies to the disrupted conformation of the DNA molecule as it exists in methanol solutions, but it may be assumed that a /D is not greatly different for the hypothetical native helical conformation in methanol. It can be concluded, therefore, that there is a net reduction in electrostatic repidsive interactions, and in electrostatic free energy, for the native conformation of DNA in methanol compared to water. Similar considerations apply in ethanol, whose dielectric constant is still smaller than that of methanol. Therefore, electrostatic factors alone would tend to stabilize the helical conformation in these nonaqueous solvents, and in spite of this, the structure is disrupted. 

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