Woodward's rules, named after

Robert Burns Woodward Robert Burns Woodward (April 10, 1917 – July 8, 1979) was an American organic chemist. He is considered by many to be the most preeminent synthetic organic chemist of the twentieth century, having made many key contributions to the subject, e ...

and also known as Woodward–Fieser rules (for

Louis Fieser Louis Frederick Fieser (April 7, 1899 – July 25, 1977) was an American organic chemist, professor, and in 1968, professor emeritus at Harvard University. He is known for inventing military effective napalm whilst he worked at Harvard in 194 ...

) are several sets of empirically derived rules which attempt to predict the

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

of the

absorption Absorption may refer to: Chemistry and biology * Absorption (biology), digestion **Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which ...

maximum (λ_max) in an ultraviolet–visible spectrum of a given

compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive struct ...

. Inputs used in the calculation are the type of

chromophore A chromophore is the part of a molecule responsible for its color. The color that is seen by our eyes is the one not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chromophore is a region in the molec ...

s present, the

auxochrome An auxochrome (from Ancient Greek ''auxanō'' "increase" and ''chrōma'' "colour") is a group of atoms attached to a chromophore which modifies the ability of that chromophore to absorb light. They themselves fail to produce the colour; but whe ...

s (substituents on the chromophores, and

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

. Examples are conjugated

carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a ...

compounds, conjugated

diene In organic chemistry a diene ( ) (diolefin ( ) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms. They thus contain two alk''ene'' units, with the standard prefix ''di'' of systematic nomenclature. ...

s, and

polyene In organic chemistry, polyenes are poly- unsaturated, organic compounds that contain at least three alternating double () and single () carbon–carbon bonds. These carbon–carbon double bonds interact in a process known as conjugation, resultin ...

Implementation

One set of Woodward–Fieser rules for

s is outlined in table 1. A diene is either homoannular with both double bonds contained in one ring or heteroannular with two double bonds distributed between two rings. With the aid of these rules the UV absorption maximum can be predicted, for example in these two compounds:''Organic spectroscopy'' William Kemp 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). In the compound on the right, the diene is homoannular with 4 alkyl substituents. 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.

References

{{reflist Physical organic chemistry Absorption spectroscopy