Woodward's rules - Simple English Wikipedia, the free encyclopedia

Woodward's rules are a set of rules about how organic chemical compounds absorb ultraviolet light.

They give information about the wavelength of the absorption maximum (symbol λ_max ) in an ultraviolet-visible (UV) spectrum of a compound. The rules are named after Robert Burns Woodward. He was a Harvard University professor who won the 1965 Nobel Prize in chemistry. The rules are sometimes called the Woodward-Fieser rules, to also honor Louis Fieser.

The rules build the prediction on the type of chromophores present, the substituents on the chromophores, and changes due to the solvent.^[1][2] Examples are conjugated carbonyl compounds,^[3][4] conjugated dienes,^[5] and polyenes.^[4]

One set of Woodward-Fieser rules for dienes is shown in table one. A diene is either homoannular with both double bonds contained in one ring or heteroannular with two double bonds distributed between two rings.

• These rules predict the UV absorption maximum of compounds. Here are two examples:^[7]

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.

1. ↑ Woodward, Robert Burns (1941). "Structure and the Absorption Spectra of α,β-Unsaturated Ketones". J. Am. Chem. Soc. 63 (4): 1123–1126. doi:10.1021/ja01849a066.
2. ↑ Louis F. Fieser, Mary Fieser, Srinivasa Rajagopalan (1948). "Absorption Spectroscopy and the Structures of the Diosterols". J. Org. Chem. 13 (6): 800–806. doi:10.1021/jo01164a003. PMID 18106021.{{cite journal}}: CS1 maint: multiple names: authors list (link)
3. ↑ Neil Glagovich (2007-07-19). "Woodward's Rules for Conjugated Carbonyl Compounds". Central Connecticut State University. Archived from the original on 2008-04-10. Retrieved 2008-05-05.
4. ↑ ^{4.0 4.1} William Reusch. "UV-Visible Spectroscopy". VirtualText of Organic Chemistry. Michigan State University. Archived from the original on 2007-10-16. Retrieved 2011-07-27.
5. ↑ Neil Glagovich (2007-07-19). "Woodward-Fieser Rules for Dienes". Central Connecticut State University. Archived from the original on 2008-04-10. Retrieved 2008-05-05.
6. ↑ Spectroscopic Determination of Organic Compounds, 5th Edition, Silverstein, Bassler, Morrill 1991
7. ↑ Organic spectroscopy William Kemp