Structural Analysis (Application of Woodward-Fieser Rules)

• It is used for finding absorption maxima position (λMax)

• This differs from observed values by 5-6%.

• Effect of substituent groups can be reliably quantified by use Woodward –Fieser Rule

• Separate values for conjugated dienes and trines and α-β-unsaturated ketnones are available

Woodward and the Fiesers performed extensive studies of terpene and steroidal alkenes and noted similar substituents and structural features would predictably lead to an empirical prediction of the wavelength for the lowest energy p p* electronic transition

This work was distilled by Scott in 1964 into an extensive treatise on the Woodward-Fieser rules in combination with comprehensive tables and examples – (A.I. Scott, Interpretation of the Ultraviolet Spectra of Natural Products, Pergamon, NY, 1964)

A more modern interpretation was compiled by Rao in 1975 – (C.N.R. Rao, Ultraviolet and Visible Spectroscopy, 3rd Ed., Butterworths, London, 1975)

• Alkenes are named by dropping the -ane ending of the parent and adding -ene.

• Conjugated :organic compound; containing two or more double bonds each separated from the other by a single bond

• Dienes: One of a class of organic compounds containing two ethylenic linkages (carbon-to-carbon double bonds) in the molecules. Also known as alkadiene; diolefin.

Endocyclic double bonds have both carbons in the ring and exocyclic double bonds have only one carbon as part of the ring. Cyclopentene is an example of an endocyclic

double bond. Methylenecylopentane is an example of an

exocyclic double bond.

Woodward Fieser Rule for Dienes & Polyenes

Woodward Fieser rule for undsaturated carbonyl compound