wood ward-fieser rule

1. Presented by :
B.Kavita
M.Pharmacy 1st yr
Department of pharmaceutical analysis

2.  Introduction .
WOODWARD- FIESER RULES .
Woodward - Fieser rules for Conjugated Dienes .
Woodward - Fieser rules for α,β - unsaturated Carbonyl compounds.
Woodward - Fieser rules for Aromatic compounds or Benzoyl derivatives.

3. INTRODUCTION
In 1945 Robert Burns
Woodward gave certain rules for
correlating λ structure. In 1959
Louis Frederick Fieser modified
these rules with more experimental
data, and the modified rule is
known as Woodward and λmax for
a given structure by relating the
position and degree of substitution
of chromophore. .

4. 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.
According to Woodward’s rules the λmax of the molecule can be calculated
using a formula:
λmax = Base value + Σsubstituent contribution + Σ Other Contributions
There are three sets of rules
1.Woodward-Fieser rule for Conjugated dienes and polyenes.
2. For - unsaturated Carbonyl compounds.
3.For Aromatic compounds or Benzoyl derivatives.

5. Woodward - Fieser rule s for
Conjugated Dienes
 Homoannular Diene:- Cyclic diene having conjugated
double bonds in same ring.
 Heteroannular Diene:- Cyclic diene having
conjugated double bonds in different rings.

6.  Endocyclic double bond:- Double bond present in a ring.
 Exocyclic double bond: - Double bond in which one of the
doubly bonded atoms is apart of a ring system. Here Ring A has
one exocyclic and endocyclic double bond. Ring B has only one
endocyclic double bond.

7. Parent values and increments for different
Substituent or Groups for Conjugated Dienes
 Parent Value
 Acyclic conjugated dienes and Heteroannular conjugated dienes 215 nm
 Homoannular conjugated dienes 253 nm
 Acyclic trienes 245 nm
 Increments
 Each alkyl substitute or ring residue 5 nm
 Exocyclic double bond 5 nm
 Double bond extending conjugation 30 nm
 Auxochromes
 -OR 6 nm
 -SR 30 nm
 -Cl,-Br 5 nm
 -NR2 60 nm
 -OCOCH3 0 nm

8. Example of Woodward - Fieser rules for
Conjugated Dienes
 (3E)-3,5-dimethylhexa-1,3-diene—ethane
(1/2)
 Parent value for Acyclic conjugated diene = 215 nm
 Alkyl Substitute or Ring residue at C-3 and C-5 = 5+5= 10 nm
 So, λmax would be = (215+10) nm = 225 nm
 Observed value = 225 + - 5nm

9. Woodward Fieser rule for alpha,betha - unsaturated
Carbonyl compounds
 Woodward-Fieser rules can be extended to calculate the λmax of
α,β-unsaturated carbonyl compounds. there is base value to which
the substituent effects can be added and the λmax can be
calculated using the formula:
λmax = Base value + Σ Substituent Contributions + Σ Other
Contributions
 In this alpha, beta unsaturated compounds the compound may be
a aldehydes or ketones.
 It may be acyclic or 6 membered or 5 membered ring systems

10. Parent values and increments for different Substituent
Groups for carbonyl compounds
 Parent Value:
 α,β -unsaturated acyclic or six memberedring ketone=215
nm
 α,β -unsaturated five membered ring ketone =202 nm
 α,β -unsaturated aldehyde=207 nm
 Increments :
 Each alkyl substitute or ring residue at α position 10 nm
 At position β=12 nm
 At β position and higher position =18 nm
 Each Exocyclic double bond =5 nm
 Double bond extending conjugation= 30 nm
 Homoannular conjugated diene =39 nm

11. Group
Alkyl R 10 nm 12 nm 18 nm 18 nm
Alkoxy OR 35 nm 30 nm 17 nm 31 nm
Hydroxyl OH 35 nm 30 nm 30 nm 50 nm
Chlorine -Cl 15 nm 12 nm 12 nm 12 nm
Bromine –Br 25 nm 30 nm 25 nm 25 nm

12. example
Parent conjugated enone
in acyclic compound = 215 nm
2 alkyl residue at position = 24 nm
λmax = 239 nm

13. Woodward - Fieser rule for Aromatic
compounds or Benzoyl derivatives
Parent values and increments for Benzoyl
Derivatives
 Parent Value:
 X = alkyl / ring residue, ArCOR 246 nm
 X = H, ArCHO 250 nm
 X = OH / O-alkyl, ArCO2H, ArCO2R 230 nm
 Increments :
 R = alkyl / ring residue o, m = 3 nm ,p = 10 nm
 R = OH / O-alkyl o, m =7 nm , p = 25 nm
 R = NH2 o, m = 23 nm, p = 58 nm

14. Values for substituents or groups
Groups Ortho position nm Meta position nm Para position nm
-OH 7 7 25
-OCH3 7 7 25
-O 11 20 78
-Cl 0 0 10
-Br 2 2 15
-NH2 13 13 58

15. example
base value = 246 nm
Hydroxy group at meta position = 07 nm
Hydroxy group at para position = 25 nm
λmax = 278 nm

16. Heterocyclic systems:
 Once again the most successful approach to the eletronic spectra
of heterocyclic system has been an empirical one , coupled with a
new guidelines on substituent effects.
 solvent used were usually hexane (H),ethanol (E) change of
solvent may affect the spectrum.
compound solvent Principal
maxima(nm)
Pyrrole E 235
Furan H 207
thiophene H 227,231,237
Pyridine H 251,256
Quinoline E 226,230
Isoquinoline H 216,266,306,318

17. Simple alkyl substituents,as usual, have little effect on the
spectra,but polar groups (electron donors) can have profound
effects, which are usually highly dependent on substitution position
in relation to the heteroatom.the possibility that tautomeric system
may be generted should also be borne in mind,the classic case here
being the 2 –hydroxypyridines,which tautomerize almost entirely to
2-pyridones, with substantial changes in the electronic spectra.

18. REFERENCES
 Woodward, Robert Burns (1941). "Structure and the
Absorption Spectra of α,β-Unsaturated Ketones". J. Am.
Chem. Soc. 63(4): 1123. doi:10.1021/ja01849a066
 A text book of organic spectroscopy by P .S Kalsi ( page
.no-40)
 A text book of uv-visible and infrared spectroscopy by raja
shekaran ( page no.88-100)
 yr. sharma, elementary organic spectroscopy pg.no:36-48
 IUPAC Gold Book heterocyclic compounds