Gas phase association

The substituted radical cations [Me2S.. SMe2], [Et2S. .SEt2] and [Et2S.. SMe2] (Fig. 4) have been studied by lilies, McKee and co-workers using a combined experimental/theoretical approach [127-129]. Mass spectrometry experiments on the gas-phase association reactions... 

K. Gragg, Chemical and Biological Characterization of Particulate-, Semi-volatile-, and Gas-Phase-Associated Compounds in Diluted Heavy-Duty Diesel Exhausts A Comparison of Three Different Semi-volatile-Phase Samplers, Environ. Sci. Technol., 25, 332-338 (1991). 

While similar data are not available for the corresponding Me3Pb+ ion, the thermochemistry of the gas-phase association of Pb+ with several molecules of NH3 and H20, and with one molecule of MeOH, MeNH2 and benzene has been thoroughly characterized168-171. By comparison with the above examples, the association of Pb+ with H20 is weaker than that of the trimethylgermanium and trimethyltin ions (see equation 24)169. 

Table 4.3 Thermodynamic Functions for Gas Phase Association of Water Molecules 2H20 (H20>2...

Table A-5. Rate-Coefficient Parameters for Gas-Phase Association Reactions, with Air Providing the Third-Body Molecule M ...

This decreases to a maximum of 4.3 for a light crude oil (API = 34) at the same temperature (Fig. 7b). Fractionation in any gas phase associated with oil decreases with increasing temperature, Vg/Vi and decreasing oil density. 

Table 2 contrasts the free energy cycle for association of a proton with NH3 (a very strong gas phase electrostatic dominated interaction) with that of two methane molecules (a very weak gas phase association). As one can see, the aqueous solution free energies are very different from those in the gas phase. 

The situation is completely different for the strong ion/polar association of NHj with H. Here the gas phase association is very favorable, but because of the much greater solution free energy of H" than NH4, the solution free energy of association is only slightly favorable, and, at pH values above the pK, AG is no longer negative. 

Ross and Subramanian [21] have suggested, on the basis of analysis of AH and 45 of protein-Ugand interactions, that a negative AH for association could come from enhanced polar interactions in the relatively lower dielectric medium of the protein (compared to water). Thus, even though such interactions are clearly less important than for gas phase association, they may contribute along with dispersion to non-covalent macromolecule hgand association. 

Boldfaced values indicate the pair that has the lowest average deviation and can be considered the best fit, For each binary system, best fits are Indicated for both the text software and the results reported with the DECHEMA data. The values reported by DECHEMA correct for gas-phase association this correction is not implemented in the text software,... 

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