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Amines
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Solvation is the process by which solvent molecules surround and interact with solute ions or molecules. Polar solutes such as alcohols, carboxylic acids, or alkoxide ions are solvated by polar solvents such as water or alcohols, but they are not solvated by non-polar solvents such as hexane. Does solvent play a role in the SN2 versus E2 reactions?
Introduction
Published in Yizhak Marcus, Solvent Mixtures, 2002
The term solvation was used in the introduction in its more colloquial sense, without being properly defined. On statistical thermodynamic grounds, solvation of a solute is defined as the process of transfer of a particle (atom, ion, aggregate, or molecule) of the moiety being solvated from a fixed position in an ideal gas phase to a fixed position in the liquid solvent solvating it [3]. This solvent may even be chemically identical with the solute itself, if liquid, the process then being condensation from the vapor. Generally, the solvent is some neat liquid, a mixture of liquids, or a solution already containing some of this solute alone or with other substances, with no restrictions on the concentrations. The fixed positions are specified in this definition in order to confine the process of solvation to the interactions of the solvated particle with its surroundings. The process is thus freed from the translational degrees of freedom of the solute, hence of the different volumes that the solute may occupy in the ideal gas phase and in the liquid solution. This convention takes care of the different standard states and concentration scales of the solute in the gas and in the liquid solution or mixture. With the process so defined, the thermodynamics of the solvation process pertain entirely to The interactions of the solute particle with its environment in the liquid phase (because in the ideal gas phase it is devoid of interactions)Changes in its internal degrees of freedom induced by these interactionsThe effects of the solute particle on its environment due to its presence and interactions
Algorithmic graph theory for post-processing molecular dynamics trajectories
Published in Molecular Physics, 2023
Sana Bougueroua, Ylène Aboulfath, Dominique Barth, Marie-Pierre Gaigeot
The 2D-MolGraphs can also be used to analyse the time evolution of the coordination number (CN) made by each ion with the water molecules once accommodated within the 2D-HBonded network of water at the interface with the air. This is illustrated in Figure 9. Such analysis is straightforwardly given by the analysis of the (blue) edges connected to the vertex of and in the 2D-MolGraphs. Over the 10 ps DFT-MD presented in Figure 9, we observe that most of the time the molecular anion is solvated by two to four water molecules of the BIL 2D-HBonded network. One can nicely see the dynamical fluctuation of the solvation shell of the ion from the plot. On the other hand, bromine is solvated by one to three water molecules of the BIL 2D-HBonded network, the plot also nicely showing the dynamical evolution of the coordination shell number. As already said above, the solvation shell and coordination numbers discussed here are related only to the water molecules that belong to the BIL interfacial layer. The subsequent Diffuse Layer is not taken into account in these analyses, it would however be straightforward to include this layer into the construction and analyses of the 2D-MolGraphs.
Uranyl Speciation in the Presence of Specific Ion Gradients at the Electrolyte/Organic Interface
Published in Solvent Extraction and Ion Exchange, 2022
Nitesh Kumar, Michael J. Servis, Aurora E. Clark
where is the continuous time duration of molecule/ion in the solvation shell or primary coordination sphere about the reference molecule/ion.[59] Nitrate ions are observed to have 10 faster dynamic exchange between the primary coordination sphere of uranyl and the second solvation shell, relative to water. Fast dynamic properties have been previously reported to be sensitive to the geometric cutoff employed to define primary and secondary regions about a solute. To investigate the sensitivity of the nitrate residence time about UO, the dynamic correction procedure of Ozkanlar et al.[58] was employed to remove the transient breaking and formation of the interaction caused by the U···ON distance cutoff. Within the correction procedure, a tolerance of 1 ps with average persistence value of 7 ps was used. The computed residence time of nitrate in the uranyl solvation shell without correction was found to be 10 ps, whereas the correction procedure yielded a very similar value of 12 ps.
Investigation of coarse-grained models across a glass transition
Published in Soft Materials, 2020
At the higher, glass phase density (left column), the AA rdf demonstrates the greatest structure at the lowest temperature ( = 270 K) and the least structure at the highest temperature ( = 400 K). However, the AA rdf calculated at the intermediate temperature = 330 K, which is near the glass transition, 343 K, appears distinct. This intermediate rdf appears very similar to the glass phase rdf in the first solvation shell, but more like the liquid phase rdf in the second solvation shell. Moreover, the MS-CG pair potential calculated near the glass transition temperature is more repulsive than the pair potentials calculated for temperatures below ( = 270 K) and above ( = 400 K) the glass transition.