1. Presentation On Ultra-violet and Visible Spectroscopy Presentation On Ultra-violet and Visible Spectroscopy 2/22/20191

2. 2 Absorption maxima in conjugated system Woodward-fieser rules for calculating absorption maximum in Dienes

3. 2/22/20193 Absorption maxima in Conjugated system CompoundTransition Ethylene17015,000 1,3-butadiene21721,000 1,3,5- hextriene25421,400

4. 2/22/20194 In case of Ethylene CCC C 170nm Energy Figure: Electronic excitation in ethylene

5. 2/22/20195 C C C C In case of 1,3-butadiene C C C C + - HOMO LUMO 217nm Energy Bonding Anti Bonding C C C C As the number of p-orbitals increases which create conjugate system the transition energy between HOMO & LUMO decreases hence wavelength increases.

6. Woodward- Fieser rule 2/22/20196 Woodward formulated certain empirical rules for calculating the absorption maximum in conjugated dienes. This were latter modified by Fieser in 1948. According to these rules, each types of diene has a certain fixed value and the value of absorption maximum depends upon: The number of alkyl substituents or ring residues on the double bond. The number of double bonds which extend conjugation & The presence of polar groups such as –Cl, -Br, -OR etc. Woodward formulated certain empirical rules for calculating the absorption maximum in conjugated dienes. This were latter modified by Fieser in 1948. According to these rules, each types of diene has a certain fixed value and the value of absorption maximum depends upon: The number of alkyl substituents or ring residues on the double bond. The number of double bonds which extend conjugation & The presence of polar groups such as –Cl, -Br, -OR etc.

7. 2/22/20197 1. Parent values for butadiene system or a cyclic conjugated system 2. Homoannular conjugated diene 3. Heteroannular conjugated diene 4. Acyclic triene 5. Increment for each substituent : Alkyl substituent or ring residue Exocyclic double bond Double bond extending conjugation Woodward- Fieser rule-Conjugated dienes and triens 217 nm 253 nm 215 nm 245 nm 5 nm 30 nm

8. 2/22/20198 Calculation Basic value (homoannular)= 253 nm 4-Ring residue (4×5)= 20 nm 2-exocyclic double bond (2×5)= 10 nm 1-double bond extending conjugation = 30 nm total= 313 nm Basic value (hetero annular)= 215 nm 4-Ring residue (5×5)= 25 nm 3-exocyclic double bond (3×5)= 15 nm 1-double bond extending conjugation = 30 nm total= 285 nm

9. Thanks to all……… 2/22/20199