Physicochemical properties, viii

A number of physicochemical properties which have been investigated for a series of simple derivatives of the different tautomeric forms of adenine, prominent among which are dipole moments and ultraviolet absorption spectra, throw additional light on the problem. Table VIII indicates the results of a theoretical evaluation of the dipole moments for the different tautomeric forms (12-19) of adenine as well as the experimental values of the moments in methyl and benzyl derivatives of these forms with the exception of the derivatives of the N(1)H form for which, unfortunately, no experimental data could be obtained because of lack of sufficiently soluble 1-substituted derivatives. 

Present knowledge of the electronic, surface, and catalytic properties of non-metals is substantially less advanced than that of metals. This is partly due to the fact that various physicochemical techniques are less rapidly applicable to non-metal catalysts. Relatively few metal oxide catalysts have been investigated by XAES techniques (Table VIII and Ref. 18). 

This theoretical conclusion has not been confirmed by direct reptation experiments, but it has some implications. Mechanical measurements on strongly entangled, high molecular weight chains may be completely dominated by the presence of a few branch points. If exponential laws such as eq. (VIII.23) are involved, we need only a small fraction of branch points, and such fractions cannot be detected by standard physicochemical methods. We conclude that mechanical measurements in long chain systems can be extremely sensitive to certain chemical defects. Unfortunately, we do not have reptation data on controlled branched polymers. We do have data on mechanical properties of branched melts,but the melt problem is much more complex than the reptation problem, as shown in next section. 

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