UV Spectra and the Structure of Organic Molecules

Empirical rules based on thousands of laboratory observations have been developed over the years relating the wavelengths of the UV absorption maxima to the structures of molecules. R.B. Woodward in 1941 and then L. Fieser and M. Fieser developed rules for predicting the absorption maxima of dienes, polyenes, and conjugated ketones by studying terpenes, steroids, and other natural products. The rules are known as Woodward s Rules or the Woodward-Fieser Rules. 

There are essentially four organic molecular systems of interest. The principal parent chromophore systems are (1) conjugated dienes, (2) monosubstimted benzene rings, (3) disubstituted benzene rings, and (4) conjugated carbonyl systems. The method of calculation is to identify a parent system and assign an absorption maximum. The parent system is then modified by the presence of other systems within the molecule. From these modifications, the absorption maximum of a specific molecular structure can be calculated. 

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