Experimental Examples

In a 100 mL round-bottomed flask coimected to a reflux condenser, 4.88 g (20 mmol) uridine 1 is suspended and stirred in 12.44 mL (60 mmol) HMDS 2, 4.15 mL (50 mmol) pyrrolidine, 0.1 mL Me3SiCl 14, and 15 mL abs. pyridine. After 4.5 h heating in an oil bath at 140-145 °C the reaction mixture turns yellowish and is complete according to TLC (acetone-methanol, 3 1). After evaporation of the solvents in vacuo, the yellowish, partly crystalline residue of crude 5 b is boiled for 3 h in 100 mL methanol and then kept at room temperature for 16 h. After evaporation of the solvent, 6.09 g crade 4-pyrrohdino-l-(79-D-ribofuranosyl)-l,2-dihydropyrimidine-2-one 6b is obtained. This is recrystallized from 90 mL boiling methanol and subsequently from 30 mL methanol to give, in two crops, 5.677 g (95.4%) pure 6b, m.p. 211-213°C [11]. 

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There are fewer experimental examples of mode specificity for the unimolecular decomposition of covalently bound molecules. One example is the decomposition of the fomiyl radical HCO, namely... 

Diflfiisive processes nonnally operate in chemical systems so as to disperse concentration gradients. In a paper in 1952, the mathematician Alan Turing produced a remarkable prediction [37] that if selective diffiision were coupled with chemical feedback, the opposite situation may arise, with a spontaneous development of sustained spatial distributions of species concentrations from initially unifonn systems. Turmg s paper was set in the context of the development of fonn (morphogenesis) in embryos, and has been adopted in some studies of animal coat markings. With the subsequent theoretical work at Brussels [1], it became clear that oscillatory chemical systems should provide a fertile ground for the search for experimental examples of these Turing patterns. 

Note 2. A large number of experimental examples are given in Ref. 108. In some cases methyl sulfonates can be successfully applied when the use of the sulfinic esters leads to mixtures of 1,1- and 1,3-substitution products. 

The experimental studies of a large number of low-temperature solid-phase reactions undertaken by many groups in 70s and 80s have confirmed the two basic consequences of the Goldanskii model, the existence of the low-temperature limit and the cross-over temperature. The aforementioned difference between quantum-chemical and classical reactions has also been established, namely, the values of k turned out to vary over many orders of magnitude even for reactions with similar values of Vq and hence with similar Arrhenius dependence. For illustration, fig. 1 presents a number of typical experimental examples of k T) dependence. 

Figure 6. An Experimental Example of the Mass Overload of Benzene...

Despite the results from various experiments such as transference number measurements, polarographic studies, spectroscopic measurements, and dielectric relaxation studies in addition to conductivity measurements, unilateral triple-ions remain a matter of debate. For experimental examples and other hypotheses for the interpretation of conductance minima the reader is referred to Ref. [15] and the literature cited there. 

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