The Woodward-Fieser rule provides a method to calculate the maximum wavelength (λmax) of absorption in the UV spectrum of conjugated dienes and trienes. It assigns base values to different diene systems and allows additions to the base value based on structural features like alkyl substituents, extended conjugation, and polar groups. Examples are provided to demonstrate calculating λmax values for compounds containing homoannular dienes, heteroannular dienes, and exocyclic and endocyclic double bonds by applying additions to the appropriate base value.

1. WOOD WARD FIESER RULE
Sushmita I Hiremath
Assistant Professor
Department of Pharmaceutical Chemistry
KLE College of Pharmacy, Hubballi.
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2. Introduction:-
Woodward Fieser rule is a simple rule used to calculate λmax of a given
organic compound.
In 1945 Robert Burns Woodward gave certain rules for correlating
λmax with molecular structure. In 1959 Louis Frederick Fieser modified
these rules with more experimental data, and the modified rule is known
as Woodward-Fieser Rules. It is used to calculate the position and
λmax for a given compound by relating the position and degree of
substitution of chromophore.
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3. Rules to calculate λmax
WOODWARD- FIESER RULES:
Each type of diene or triene system is having a certain fixed value at
which absorption takes place; this constitutes the Base value or Parent
value. The contribution made by various alkyl substituents or ring
residue, double bond extending conjugation and polar groups such as –
Cl, -Br etc are added to the basic value to obtain λmax for a particular
compound.
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4. CONJUGATED DIENE CORRELATIONS:
a) Homoannular Diene:- Cyclic diene having conjugated double bonds
in same ring.
b) Heteroannular Diene:- Cyclic diene having conjugated double bonds
in different rings.
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5. c) Endocyclic double bond:- Double bond present in a ring.
d) Exocyclic double bond: - Double bond in which one of the doubly
bonded atoms is a part of a ring system.
Here Ring A has one exocyclic and endocyclic double bond. Ring B has
only one endocyclic double bond.
CH2
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6. CONJUGATED DIENE CORRELATIONS:
i) Base value for homoannular diene = 253 nm
ii) Base value for heteroannular diene = 215 nm
iii) Alkyl substituent or Ring residue attached to the parent diene = 5 nm
iv) Double bond extending conjugation = 30 nm
v) Exocyclic double bonds = 5 nm
vi) Polar groups: a) –O Ac = 0 nm
b) –O Alkyl = 6 nm
c) -Cl, -Br = 5 nm
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7. EXAMPLES
1) Calculate the absorption maximum in the UV spectrum of 2,4
hexadiene
Butadiene system, base value = 217nm
2 alkyl substituents (2 x5) = 10nm
Calculated value = 227nm
Observed value = 227nm
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C
H3
CH3

8. 2)Calculate λmax of 1,4 –dimethyl cyclohex 1,3 diene
Parent value for homoannular ring =253nm
Two alkyl substituents =10nm
Two ring residue =10nm
Calculated value = 273nm
Observed value =263nm
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CH3
C
H3

9. • 3) Allylidiene cyclohexane
• Parent value for acyclic butadiene = 217nm
• One exocyclic conjugation = 5nm
• Two ring residue (2x5) = 10nm
• Calculated value = 232nm
• Observed value = 237nm
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CH2

10. • 4)Isoprene
• Acyclic butadiene = 217nm
• One alkyl substituent = 5nm
• Calculated value = 222nm
• Observed value = 220nm
C
H2
CH2
C
H3
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11. • 5) Calculate λmax for
• Parent value for homoannular ring = 253nm
• Extended conjugation = 30nm
• Exocyclic conjugation = 5nm
• 6 ring residue (6x5) = 30nm
• Calculated value = 318nm
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12. Reference:
• Textbook of organic spectroscopy by William Kemp 3rd edition
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13. THANK YOU
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