Woodward Fieser Rule for Calculating λmax in α, β Unsaturated Carbonyl Compounds
Woodward Fieser Rule for Calculating λmax in α, β Unsaturated Carbonyl Compounds or Enones and Dienones
Woodward and Fieser formulated emperical rules for calculating the wavelength of absorption maximum (λmax) for α, β Unsaturated Carbonyl Compounds or Enones and Dienone. These rules were later modified by Scott.Rules for Calculation λmax in α, β Unsaturated Carbonyl Compounds
Base values:1. Acyclic α,β-unsaturated ketones 215 nm
2. 6-membered cyclic α,β-unsaturated ketones 215 nm
3. 5-membered cyclic α,β-unsaturated ketones 202 nm
4. α,β-unsaturated aldehydes 210 nm
5. α,β-unsaturated carboxylic acid and esters 195 nm
Increments for:
1. Double bond extending conjugation (DEC): +30 nm
2. Exocyclic double bond: +5 nm
3. Homodiene component: +39 nm
4. Alkyl group/ring residue-
a. α +10 nm
b. β +12 nm
c. γ and higher +18 nm
6. Polar groups:
| Group | α | β | γ | δ and Higher |
|---|---|---|---|---|
| -OH | +35 | +30 | - | +50 |
| -OAc | +6 | +6 | +6 | +6 |
| -Cl | +15 | +12 | - | - |
| -Br | +25 | +35 | - | - |
| -OR | +35 | +30 | +17 | +31 |
| -SR | - | +85 | - | - |
| -NR2 | - | +95 | - | - |
Base Value: 215 nm
Two β alkyl: 24 nm
Calculated Value: 239 nm
λmax Observed Value: 237 nm
Base Value: 215 nm
One α-OH: 35 nm
One β ring residue: 12 nm
One β alkyl: 12 nm
Calculated Value: 274 nm
λmax Observed Value: 275 nm
Base Value: 215 nm
One doubel bond extending conjugation: 30 nm
One β-ring residue: +12 nm
One δ ring residue: +18 nm
Two Exocyclic double bond: +5 nm
Calculated Value: 280 nm
λmax Observed Value: 280 nm
Base Value: 202 nm
Exocyclic double bond: +5 nm
Two β-ring residue: +24 nm
Calculated Value: 231 nm
λmax Observed Value: 226 nm
Base Value: 215 nm
One doubel bond extending conjugation: 30 nm
Homocyclic Diene: 39 nm
One δ ring residue: 18 nm
Calculated Value: 302 nm
λmax Observed Value: 300 nm
