Woodward's rules, named after Robert Burns Woodward and also known as Woodward–Fieser rules (for Louis Fieser) are several sets of empirically derived rules which attempt to predict the wavelength of the absorption maximum (λmax) in an ultraviolet–visible spectrum of a given compound.
With the aid of these rules the UV absorption maximum can be predicted, for example in these two compounds:[8]
In the compound on the left, the base value is 214 nm (a heteroannular diene).
This diene group has 4 alkyl substituents (labeled 1,2,3,4) and the double bond in one ring is exocyclic to the other (adding 5 nm for an exocyclic double bond).
Both double bonds in the central B ring are exocyclic with respect to rings A and C. For polyenes having more than 4 conjugated double bonds one must use Fieser–Kuhn rules.