Solutions and Neat Liquids

Every solvent has its own absorption bands in the MIR region. For this reason, the most appropriate solvent for the given situation has to be chosen from a whole selection. Unfortunately this selection does not include water and alcohols, which exhibit broad and strong bands in their MIR spectra. Moreover, many optical materials used as MIR windows for liquid cells (e. g. alkali hahdes, such as KBr) are soluble in water and alcohol. The solvents with the largest absorption free areas in the MIR are carbon tetrachloride and carbon disulfide. Both solvents are quite toxic and must be handled carefuUy. A Hst of the most common MIR solvents is 

Windows for liquid cells typically consist of NaCl or KBr for non-aqueous samples or Cap2 for aqueous solutions. A list of common MIR window material is given in Chapter 5. 

For the selection of optical windows, besides such parameters as useful spectral range, mechanical resistance and solubility, the refractive index also has to be taken into account The refractive index of the windows should match that of the liquid sample in order to minimize reflection losses, stray light and distortions of band shapes (Christiansen effect). NaCl and KBr are very suitable for organic analytes. Inorganic analytes may have much higher refractive indices. The higher the refractive index, the higher the reflection losses for the incident IR radiation. 

Neat liquids require a film thickness in the 10 pm range. Since it would be difficult to fill a cell of such low thickness, and even more difficult to clean it, capillary films of such a sample are usually formed by squeezing a few drops of compound between two windows 

In the case of relatively low-melting solids it is also possible to prepare a thin film by melting and squeezing the sample between two windows. Thin films of nonvolatile liquids or solids can be deposited on the window by solvent evaporation. The sample is first dissolved in a volatile solvent A few drops of the solution are placed on the window. After evaporation of the solvent, a thin film of sample is obtained on the window. The windows can usually be cleaned using carefully dried methylene chloride or acetone. Preparing a thin film from solution or sohdification from the melt are methods well suited to the examination of amorphous materials, such as waxes or soft resins. 

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Washes. Several types of solutions or liquids can be used to collect handwash samples, including various types of aqueous surfactant solutions, and neat isopropanol or ethanol. The physico-chemical properties of the pesticide should guide selection of the rinse solvent, especially the octanol-water partition coefficient... 

ROA is about one order of magnitude larger and one can measure vibrations which cannot be observed in solutions or neat liquids. But one has to be careful not to observe artifacts produced by the linear birefringence of the crystals. An interesting class of crystals are the cubic crystals of the sodium halogenates. These are composed of achiral subunits that form a... 

Shift measured between dilute nonpolar solution and neat sample. Similar effects occur on a change of state gas to liquid. 

Figure Bl.22.8. Sum-frequency generation (SFG) spectra in the C N stretching region from the air/aqueous acetonitrile interfaces of two solutions with different concentrations. The solid curve is the IR transmission spectrum of neat bulk CH CN, provided here for reference. The polar acetonitrile molecules adopt a specific orientation in the air/water interface with a tilt angle that changes with changing concentration, from 40° from the surface nonnal in dilute solutions (molar fractions less than 0.07) to 70° at higher concentrations. This change is manifested here by the shift in the C N stretching frequency seen by SFG [ ]. SFG is one of the very few teclnhques capable of probing liquid/gas, liquid/liquid, and even liquid/solid interfaces.

Because dimethyl sulfate looks like water, operations are preferably not performed when water is present, eg, wet floors or rain. Any spills or leaks should not be left unattended they should be contained, and mnoff to sewers should be avoided. Minor spills should be flooded with water to dilute and hydroly2e the dimethyl sulfate. The area should then be covered with a dilute (2—5 wt %) caustic solution or a dilute (2—5 wt %) ammonia solution, or soda ash may be sprinkled over the neat liquid and the mix wetted with a gende spray of water. The neutrafi2ing agent should remain on the affected area for 24 h and then should be washed away. Only personnel wearing protective equipment should perform these operations. The product bulletins should be consulted for procedures to be followed for more severe spills. Concentrated ammonia should not be used with neat dimethyl sulfate because explosions have resulted after their contact (128). 

In the first example of applications of the theory in this chapter, we made a point with respect to the polarizability of molecules and showed how the problem could have been handled by the RISM-SCF/MCSCF theory. However, the current level of our method has a serious limitation in this respect. The method can handle the polarizability of molecules in neat liquids or that of a single molecule in solution in a reasonable manner. But in order to be able to treat the polarizability of both solute and solvent molecules in solution, considerable generalization of the RISM side of the theory is required. When solvent molecules are situated within the influence of solute molecules, the solvent molecules are polarized differently depending on the distance from the solute molecules, and the solvent can no longer be neat. Therefore, the polarizable model developed for neat liquids is not valid. In such a case, solvent-solvent PCF should be treated under the solute... 

So far, there have been few published simulation studies of room-temperature ionic liquids, although a number of groups have started programs in this area. Simulations of molecular liquids have been common for thirty years and have proven important in clarifying our understanding of molecular motion, local stmcture and thermodynamics of neat liquids, solutions and more complex systems at the molecular level [1 ]. There have also been many simulations of molten salts with atomic ions [5]. Room-temperature ionic liquids have polyatomic ions and so combine properties of both molecular liquids and simple molten salts. 

The modihcation of polymer surfaces by graft copolymerization of a monomer or monomers from active sites has been reported in numerous references [165-169]. The most common techniques are y- and EB radiations, which generate surface radicals. Monomers can be present in gas phase (sublimed solid), in solution or as neat liquid. 

Since 4 has a high inclusion ability for a wide variety of organic compounds 46), it might be useful for various reaction controls. For example, 4 was found to be useful for a selective synthesis of the P-lactam 89 from N,N-diisopropylaeetylformamide (88). Irradiation of 88 in benzene solution and in neat liquid has been reported to give the oxazolidinone derivative 90 exclusively in 86 and 65% yields, respectively, but not any 89 Control of the photocyclization of 88 has been attempted by irradiation... 

Table 3 shows conductivity of 2mol/dm3 solutions of EMImBF4 and EMImPF6 in a number of molecular solvents. A high increase of conductivity, in comparison to neat ionic liquids, can be observed after dilution with electrically neutral molecular liquids. However, solutions of ionic liquids in molecular liquids are simply conventional solutions of organic salts in nonaqueous solvents, and no distinction can be seen between them and commonly employed solutions of (C2H5)4NBF4. 

For an isochratic system, you usually use a single solution, or a neat liquid, and put it into the solvent reservoir, generally a glass bottle with a stopcock at the bottom to let the solvent out (Fig. 111). The solvent travels out of the bottom of the reservoir and usually through a solvent filter that traps out any fairly large, insoluble impurities that may be in the solvent. 

Although the lower alcohol homologues such as MeOH and EtOH can be oxidized electrochemically in aqueous solution, the mechanism is complex and barely investigated [6]. Electrolysis of the neat liquid is one way to achieve the direct oxidation of MeOH and EtOH [7]. 

Andrews and co-workers have recently reported (5) C1- C1 and i 0- 0 isotopic shifts for the infrared spectrum of argon matrix-isolated FCIO2. Tantot (282) has studied in his thesis work the infrared and Raman spectra of the gas, the Raman spectrum of the neat liquid and of HF solutions, and the infrared and Raman spectra of the solid. 

Dithiazolyl radicals (58) do not dimerize at low temperatures in diluted solutions, do not react with O2, are stable to photolysis (at 350 nm), heat and in aqueous solutions at or above pH8 <83JCS(F1)925>. This makes them different from 1,3,2-dithiazolidinyl radicals. In 1987 <87CC66> solutions of (58 R = CF3) have been shown to contain 65% of the free radical and 35% of the diamagnetic dimer the concentration of the radical in concentrated solutions does not change with temperature indicating an almost zero enthalpy of dimerization. The latter in neat liquid is —3.5... 

Tetracarbonylfoctahydrotriborato(l-)] manganese is an air-sensitive liquid that decomposes slowly (about 5% in 4 days) at room temperature as a neat liquid in a vacuum. It is soluble in benzene, toluene, dichloromethane, diethyl ether, and tetrahydrofuran (THE), but decomposes upon heating at reflux in these solvents (especially in THF). Gas-phase thermal decarbonylation or solution photodecarbonylation of (CO)4Mn(B3H8) yields the novel and reactive compound (CO)3Mn(B3H8), in which the octahydrotriborate(l-) ligand is tridentate.3... 

The recorded angle of rotation of an optically active gas, liquid, solid or solution is called optical rotation and is denoted by the symbol a. The magnitude of the optical rotation (a) of a pure liquid is affected by the cell path length, density, temperature and wavelength. Hence, the specific rotation of pure (neat) liquids is defined as follows ... 

To a stirred solution (0 °C) of 10 mmol of (- )-(S)-a-(methoxymethyI)benzenccthanamine dissolved in 30 mL of benzene (previously washed with concentrated sulfuric acid and distilled) are added 10 mmol of the pure aldehyde. An immediate cloudiness usually results on addition of the aldehyde. The mixture is allowed to warm to r.t. and 15 g of anhyd Na2S04 are added. After stirring the mixture an additional 30-40 min, it is filtered and the Na2S04 washed thoroughly with dry diethyl ether. The solvent is removed by evaporation, first with aspirator pressure and then with the vacuum pump (0.5 Torr) to generally furnish 9.5-10 mmol of the aldimine as a colorless oil. The aldimines are dissolved in THF (0.4 M) and stored at — 20 to — 30 °C. Attempts to store the aldimines as neat liquids results in deterioration. As solutions, the aldimines can be conveniently transferred via syringe to reaction vessels. 

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