Woodward Fieser Rule for Calculating λ_max in α, β Unsaturated Carbonyl Compounds

Woodward Fieser Rule for Calculating λ_max in α, β Unsaturated Carbonyl Compounds or Enones and Dienones

Woodward and Fieser formulated emperical rules for calculating the wavelength of absorption maximum (λ_max) for α, β Unsaturated Carbonyl Compounds or Enones and Dienone. These rules were later modified by Scott.

Rules for Calculation λ_max 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	-	-

Examples-

Base Value: 215 nm
Two β alkyl: 24 nm
Calculated Value: 239 nm
λ_max 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
λ_max 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
λ_max Observed Value: 280 nm


Base Value: 202 nm
Exocyclic double bond: +5 nm
Two β-ring residue: +24 nm
Calculated Value: 231 nm
λ_max 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
λ_max Observed Value: 300 nm

Fieser-Kuhn Rules for Calculating λmax in Polyenes

Woodward Fieser Rule for Calculating λmax in Dienes