What To Look for in an Ultraviolet Spectrum A Practical Guide

17 WHAT TO LOOK FOR IN AN ULTRAVIOLET SPECTRUM A PRACTICAL GUIDE 

It is often difficult to extract a great deal of information from a UV spectrum used by itself. It should be clear by now that a UV spectrum is most useful when at least a general idea of the structure is already known in this way, the various empirical rules can be apphed. Nevertheless, several generahzations can 

In polynuclear aromatic substances, a third band appears near 200 nm, a band that in simpler aromatics occurs below 200 nm, where it cannot be observed. Most polynuclear aromatics (and heterocyclic compounds) have very characteristic intensity and band-shape (fine-structure) patterns, and they may often be identified via comparison to spectra that are available in the literature. The textbooks by Jaffe and Orchin and by Scott, which are listed in the references at the end of this chapter, are good sources of spectra. 

Simple ketones, acids, esters, amides, and other compounds containing both K systems and un- 

)S-unsaturated esters and acids, Nielsen s Rules (Section 7.13) may be used to predict the position of. l ax with increasing conjugation and substitution. 

17 What to Look for in an Ultraviolet Spectrum A Practical Guide 413 

Cyanidin chloride (an anthocyanin, another class of plant pigments) 

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