Solvents chemical elucidation

In general catalytic measurements in aqueous solutions are easier to interpret with certainty than those in other solvents, since our knowledge of the properties of solutions (especially of electrolytes) is very limited outside water. However, it is often necessary to use nonaqueous solvents for practical reasons e.g., solubility and chemical inertness, and the use of different solvents has elucidated a number of points of interest in the general theory of acid-base catalysis. 

Hyland, L., Toma.szek, T, and Meek, T, 1991. Human immunodeficiency viru.s-1 protease 2 Use of pH rate. studies and solvent isotope effects to elucidate details of chemical mechanism. Biochemistry 30 8454-8463. 

The authors [33] have elucidated the linear dependence of Ao0 (z-dep) on E for the polyanions by a quantum chemical consideration. A model Hamiltonian approach to the charge transfer (CT) interaction between a polyanion and solvents has been made on the basis of the Mulliken s CT complex theory [34]. 

Several modem analytical instruments are powerful tools for the characterisation of end groups. Molecular spectroscopic techniques are commonly employed for this purpose. Nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and mass spectrometry (MS), often in combination, can be used to elucidate the end group structures for many polymer systems more traditional chemical methods, such as titration, are still in wide use, but employed more for specific applications, for example, determining acid end group levels. Nowadays, NMR spectroscopy is usually the first technique employed, providing the polymer system is soluble in organic solvents, as quantification of the levels of... 

Microwave-assisted synthesis is attractive to researchers for many reasons, including speed, yields, and the potential for reduced solvent use. Raman monitoring offers a convenient way to elucidate the chemical mechanism while instantly, continuously monitoring reaction kinetics. This enables rapid, data-driven process optimizations without concerns about safely and accurately sampling out of a microwave vessel stopped mid-reaction. Pivonka and Empheld of AstraZeneca Pharmaceuticals describe the continuous acquisition of Raman spectra of an amine or Knoevenagel coupling reaction in a sealed microwave reaction vessel at elevated temperatures and pressures [134]. 

Combination of the results with solvent extraction/liquid chromatography data may elucidate the role of free, unreacted monomer in the post-curing process. The main conclusions have already appeared elsewhere (9). Here we report in much more detail on the experimental techniques as well as on new results on the delay of shrinkage with respect to chemical conversion. 

There is much scope for further work on these lines to elucidate the importance of various aspects of the solvent structure on the rate of chemical reactions in solution. It is to be hoped that these comments will encourage further interests in this subject. 

This chapter deals with silyl-substituted carbocations. In Section II results of quantum chemical ab initio calculations of energies and structures of silyl-substituted carbocations are summarized1. Throughout the whole chapter results of ab initio calculations which relate directly to the experimental observation of silyl-substituted carbocations and their reactions are reviewed. Section m reports on gas phase studies and Section IV on solvolytic investigations of reactions which involve silyl-substituted carbocation intermediates and transition states. Section V summarizes the structure elucidation studies on stable silyl-substituted carbocations. It includes ultra-fast optical spectroscopic methods for the detection of transient intermediates in solution, NMR spectroscopic investigations of silyl-substituted carbocations in superacids and non-nucleophilic solvents, concomitant computational studies of model cation and X-ray crystallography of some silyl-substituted carbocations which can be prepared as crystals of salts. 

The chemical and spectroscopic properties of the cofactor F-430 have been reviewed [98,99], The structure of the macrocycle (Figure 4) was elucidated by x-ray crystallography and NMR spectroscopy [100], The free cofactor, which is present in substantial amounts in the cells, has an absorption maximum at 430 nm, hence its name. In the enzyme, the absorption maximum is blue shifted to 420 nm. The pentamethyl ester of F-430 is soluble in organic solvents and can be reduced to the Ni(I) state under aprotic conditions, resulting in an absorption peak shift to 382 nm [101], or can be oxidized to the Ni(III) state, giving an absorption peak at 368 nm [102],... 

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