Exchangeability experiment

Di Bari L, Kowalewski J and Bodenhausen G 1990 Magnetization transfer modes in scalar-coupled spin systems investigated by selective 2-dimensional nuclear magnetic resonance exchange experiments J. Chem. Rhys. 93 7698-705... 

Protonated methanes and their homologues and derivatives are experimentally indicated in superacidic chemistry by hydrogen-deuterium exchange experiments, as well as by core electron (ESCA) spectroscopy of their frozen matrixes. Some of their derivatives could even be isolated as crystalline compounds. In recent years, Schmidbaur has pre-... 

Electrophilic Attack. A variety of boranes, heteroboranes, and metaHaboranes undergo electrophilic substitution. SusceptibiUty of boranes to electrophilic attack is often detected by deuteron—proton exchange experiments. Eor example, electrophilic hydrogen—deuterium exchange of occurs at the l-,2-,3-, and 4-positions when exposed to DCl in the presence of AlCl (81). The trend to increasing positive sites in is... 

Comparison of UV data for 3-aminoisothiazoles with those of reference compounds confirms that they exist in the 3-amino form. A more recent investigation of 4-aminoisothiazole (76MI41701) using deuterium exchange experiments of the type described in Section 4.01.5.2, and analysis of the symmetric and antisymmetric NH2 stretching frequencies in its IR spectrum, show that this compound also exists in the 4-amino form. 

Boyer s 0 Exchange Experiment Identified the Energy-Requiring Step... 

The experiment was carried out with (i )-(-)-2[l-(methoxycarbonyl)ethyl]benzene-diazonium chloride (6.80). The product, methyl 3-methyl-3-//-indazole-3-carboxylate (6.81), was racemic. With regard to the inconclusive H/D exchange experiments one therefore has to conclude that the cyclization of the diazo-methylene intermediate 6.75 is faster than the rate of deuterium incorporation. 

Note that the type of exchange experiment just discussed is now carried out infrequently. Quite clearly, the experiments can be tedious, requiring many samples, separations, and analyses. In many systems, but not all, comparable data can be obtained by the NMR methods described in Chapter 11. 

These data confirm the sequence similarity of the three nitrogenases and indicate that cofactor exchange experiments are relatively straightforward. However, the environment of the cofactor clearly affects the substrate reduction activity, as observed with mutations in... 

Equilibrium exchange experiments. In this situation, the unidirectional flux of isotopically labelled glucose across the membrane is measured as a function of the glucose concentration, which is kept equal on both sides of the membrane. Because the unidirectional influx and efflux at any particular concentration are necessarily equal, the equilibrium-exchange (ee) flux is characterized by a single V ax value, and a single Km value. A . 

The stoichiometry of the compound was investigated by isotope exchange experiments along the lines described in the preceding section. The pure... 

Molecular mobility (dynamics) 0.5-500 nm Relaxation times and line-shapes multidimensional exchange experiments... 

The benzilic acid rearrangement, though catalyzed by hydroxide ion, probably belongs in the same category as carbonium ion rearrangements. Kinetic and isotopic exchange experiments show that there is a rapid reversible addition of hydroxide ion.841 242... 

Exchange experiments (H/D) carried out under the conditions of catalysis but without ethylene showed that the C-H bond cleavage is facile and unselective (Equation (52)). However, such processes must be rapid and reversible.52,54... 

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