Woodward's rules
Woodward - Fieser rules, named after Robert Burns Woodward, Louis Frederick Fieser and Mary Fieser - also known as Woodward rules - are empirically determined rules for the analysis of UV spectra of alkenes - especially of terpenes and steroids. They allow the prediction of lambda max of the π → π * band of many dienes and polyenes other. The Woodward - Fieser rules were developed in the 1940s and have proven to be useful for the structure elucidation of many organic chemical compounds, especially in natural products.
Implementation
First you go in the application of the Woodward- Fieser rules from a baseline value of lambda max for the Stammchromophor. Then are added to the underlying depending on the substitution pattern and other structural parameters up to the solvent specific increments. Examples are α, β -unsaturated carbonyl compounds, conjugated dienes, and polyenes.
Examples of dienes the Woodward- Fieser rules are explained in the table. A diene is either homoannular (two conjugated double bonds in the same ring ) or heteroannular (two conjugated double bonds on two rings).
This according to the Woodward - Fieser rules theoretically calculated maximum absorption lambda max of the π → π * band agrees generally consistent with an accuracy of about ± 3 nm with the experimentally determined value.