IGNOU BCHET 147 2026 - Explain Woodward rules for predicting π − π abs

Question

Explain Woodward rules for predicting π − π absorption in dienes.

10 Jan 2026

Answer :

Word Count : 245

In the context of UV spectroscopy and conjugated systems such as poly nuclear hydrocarbons, Woodward’s rules provide an empirical method to predict the wavelength of π − π* electronic transitions in conjugated dienes. These rules are particularly useful in bioinorganic chemistry for understanding the electronic absorption of conjugated ligands coordinated to metal centers and in organometallic chemistry for predicting the UV absorption of conjugated π-ligands in complexes. According to Woodward, the base value of λ_max for an open-chain conjugated diene in an s-trans configuration is 214 nm, whereas for an s-cis configuration it is 253 nm. Each substituent

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