Groups, functional, influence

Examples of the operation of both types of effect have been documented. Nevertheless, while these effects are useful concepts, as mentioned previously, very often the role of the metal ion in a given in situ reaction may be quite complex and, for instance, involve aspects of both effects. As well, the metal may play less obvious roles in such processes. For example, it may mask or activate individual functional groups or influence the reaction in other ways not directly related to the more readily defined steric influences inherent in both template effects. 

The particular array of chemical shifts found for the nuclei of a given polymer depends, of course, on such factors as bond orientation, substituent effects, the nature of nearby functional groups, solvation influences, etc. As a specific example, derivatives of the carbohydrate hydroxyl moieties may give rise to chemical shifts widely different from those of the unmodified compound, a fact that has been utilized, e.g., in studies (l ) on commercially-important ethers of cellulose. Hence, as illustrated in Fig, 2, the introduction of an 0-methyl function causes (lU,15) a large downfield displacement for the substituted carbon. This change allows for a convenient, direct, analysis of the distribution of ether groups in the polymer. Analogously, carboxymethyl, hydroxyethyl and other derivatives may be characterized as well... 

In view of the clear relationship between pX-changes and absorption spectra, a study of the influences of substituents and other consitutional changes upon such spectra has a very direct bearing upon the field of acid-base properties in excited states. For example, the —OH and —0 groups function as different substituents at the 2-position in naphthalene. Any theory which accounts for their different effects upon the naphthalene transitions therefore automatically also explains the change in the naphthol-naphtholate equilibrium upon excitation. The search for linear free energy relationships in electronic spectra will therefore continue to impinge upon this field. 

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