RESUMEN
Enantiopure forms of alpha,alpha'-bis(trifluoromethyl)-9,10-anthracenedimethanol and the corresponding perdeuterated isotopomers were prepared. The conformational study was carried out by (1)H NMR, and the absolute configuration was determined by the X-ray study of the crystallized diastereoisomeric carbamate derivative. This compound was tested as a chiral solvating agent (CSA). The results showed very good discrimination for several racemic mixtures that improved other classical methods. The study of diastereomeric complexes was carried out by determination of the stoichiometry of the complex and the binding constant of the equilibrium.
RESUMEN
Undesirable temperature gradients in a NMR sample tube are usually generated by an inappropriate temperature regulation system. We have shown that such convection effects can greatly distort the measurement of translational self-diffusion coefficients. The use of sample spinning helps to minimize such undesirable effects by disruption of convection fluxes due to resulting Coriolis forces that have a strongly stabilizing effect on the conducting state of the system (J. Lounila et al., J. Magn. Reson. A 118, 50 (1996)). This simple trick allows the accurate measurement of diffusion coefficients for a wide range of temperatures and solvents without the need for a convection-compensated NMR pulse sequences or more sophisticated temperature control units. Experimental data obtained for some target compounds dissolved in several common deuterated solvents at different temperatures are reported and discussed.
RESUMEN
A convergent "5 + 1" and "5 + 3" synthetic strategy allowed the synthesis of the first examples of bis-betaines 2 and 3, a prototype of phanes that incorporate heterocyclic betaines. The structure of the quadrupolar macrocyclic systems 2 and 3 together with the dicationic [1(6)]- and [1(8)] meta-heterophane precursors 5*2X and 6*2X were examined by spectroscopy using 1H and 13C NMR techniques together with 1H-DNMR studies and electrospray ionization mass spectrometry.