Pressure solvent dependence

Several authors [36-38] have measured the pressure/solvent dependency of some unimolecular rate processes of ground-state molecules and all of the authors have interpreted the results as "dynamic solvent effects. However, as a result of our own measurements described in this chapter, we believe that what they observed was static pressure/solvent effects. See also Sect. 3.5. 

The analysis of recent measurements of the density dependence of has shown, however, that considering only the variation of solvent structure in the vicinity of the atom pair as a fiinction of density is entirely sufficient to understand tire observed changes in with pressure and also with size of the solvent molecules [38]. Assuming that iodine atoms colliding with a solvent molecule of the first solvation shell under an angle a less than (the value of is solvent dependent and has to be found by simulations) are reflected back onto each other in the solvent cage, is given by... 

H type columns must be used at a flow rate and pressure drop below maximum values listed in Tables 4.12-4.16. Standard flow rates are also listed in these tables. They are flow rate range recommendable for long-term usage in tetrahydrofuran at 25°C and vary with temperature. H type columns can be operated at a higher flow rate at elevated temperatures. They also vary with solvent depending on the viscosity. They are approximately inversely proportional to the solvent viscosity. The maximum pressure drop listed in the tables is for one column. When some columns are used in series, the total maximum pressure drop is a summation of values of all columns. 

The mean distance between two solutes at 0.02 M concentration is roughly the same as in the gas phase at one atmosphere pressure.1 Depending on the sizes of solute and solvent, about 4-12 solvent molecules make a cage. A solute molecule enclosed in... 

The plot of the pressure drop depending on the bulk velocity in adiabatic and diabatic flows is shown in Fig. 3.6a,b. The data related to the adiabatic flow correspond to constant temperature of the fluids Tjn = 25 °C, whereas in the diabatic flow the fluid temperature increased along micro-channel approximately from 40 to 60 °C. It is seen that in both cases the pressure drop for Habon G increases compared to clear water. The difference between pressure drop corresponding to flows of a surfactant solution and solvent increases with increasing bulk velocity. 

The regioselectivity of the Diels-Alder reaction depends on the number and nature of substituents on diene and dienophile and on the reaction conditions (catalyst, temperature, pressure, solvent, etc.). Generally, 1- and 2-substituted... 

The study of high pressure cycloaddition reactions of tropone (125) with maleic anhydride and norbornene allowed the reaction activation volumes to be measured and showed that they are large, negative and solvent-dependent (Scheme 5.17) [43a]. 

The magnitude of the pressure wave depends on the saaple size. It aay also prolong the duration of the pressure wave. If the sane anount of substance is injected in different solvent volumes, the peak areas will not necessarily be the same. 

For a polymorphic drug, the polymorph obtained depends on the physical conditions, such as temperature, pressure, solvent, and the rate of desupersaturation. For a solvated drug, in addition to these conditions, the thermodynamic activity of the solvating solvent may also determine the solvate obtained. However, kinetic factors may sufficiently retard the crystallization of a stable form or the solid-state transition to the stable form that an unstable form may be rendered metastable. 

The workup of the final product is similar to that outlined in Procedure 3-1, i.e., extraction of the product with ether followed by a wash with cold water, aqueous 5 % sodium carbonate solution, and water followed by drying with anhydrous sodium sulfate. The solvent then is removed under reduced pressure and, depending on the properties of the final product, purification is accomplished either by distillation under reduced pressure at temperatures below 40°C or by recrystallization from an ether-pentane mixture. In the case of unstable nitrosoamides, these operations have to be carried out at 0°C. 

The boiling-point elevation of a solution relative to that of a pure solvent depends on the concentration of dissolved particles, just as vapor-pressure lowering does. Thus, a 1.00 m solution of glucose in water boils at 100.51°C at 1 atm pressure (0.51°C above normal), but a 1.00 m solution of NaCl in water boils at... 

The amount of osmotic pressure between solution and pure solvent depends on the concentration of solute particles in the solution according to the equation... 

Due to its compressibility in the liquid (near the critical point) and in the supercritical fluid state, the dielectric constant and density, and thus the solvent quality of C02, are tunable with pressure and temperature (Keyes and Kirkwood, 1930). As illustrated in Figure 1.2, this compressibility provides for control of the density and therefore solvent-dependent properties such as dielectric constant and overall solvent strength (Giddings et al., 1968). While supercritical C02 can have high liquidlike densities, it shares many of the... 

Useful for solvents, depending on their melting temperature and vapor pressure. 

The data in Table 5 show that ap values for DPBF and 2,3-dimethylindole (DMI) are larger in SDS than in CTAB micelles. This conclusion is further stressed if kQ values are compared. Because the rate constants of the compounds considered are extremely solvent dependent, increasing with the solvent polarity (see Sec. IV), the differences observed between both surfactants could reflect a higher exposure to water in SDS micelles than in CTAB as a consequence of its smaller, more open structure [27], Furthermore, because those reactions take place with a negative activation volume [11], the observed differences between both micelles could be due, at least partially, to the smaller Laplace pressure of the larger micelle [28],... 

The density, d, of a solvent depends on both the temperature and the pressure and its value at ambient conditions is an important characteristic. Most solvents at 25°C and 0.1 MPa have densities between those of w-pentane (0.62319 g cm-3) and of tetrachloromethane... 

The up to now most frequently used techniques as, for example, vapour pressure osmometry (VPO) or freezing point depression (with its limitation regarding the solvent dependent measuring temperature) are based upon the colligative properties of the system the classical absolute light-scattering and ultracentrifugation techniques are only occasionally and approximately applicable with respect to the determination of CMC values. Evaluation of critical micelle concentrations which are based on these latter methods suffer considerably from the insensitivity of these techniques if measurements below the CMC, i.e., below about 10-3 mol dm-3, are carried out. More sensitive methods will be discussed below. 

As in the case for adsorption (see Section 2.2), in equilibrium, the quantity N of a given solute which is dissolved in a given solvent depends on its gas phase partial pressure (fugacity) P and on the temperature T, and a basic phenomenological description of the equilibrium is specification of the functional relationship between N, P, and T. At sufficiently low pressures, it is expected that the pressure dependence is linear (Henry s law) ... 

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