Woodward__fieser Rule

By Faizan Ahmed

1. WOODWARD_FIESER RULE Presented By Faizan Ahmed Md Israeel First Year M.Pharm. Department of Pharmaceutical Chemistry R. C. Patel Institute of Pharmaceutical Education and Research 1

2. CONTENTS Introduction Basic Terminologies Woodward_Fieser Rules For Dienes Woodward_Fieser Rules For Aromatics Woodward_Fieser Rules For α , β -unsaturated Carbonyl Compounds (Enones ) Fieser_Kuhn Rule References 2

3. WOODWARD_FIESER RULE Robert Burns Woodward Louis Frederick Fieser 3

4. INTRODUCTION In 1945 Robert Burns Woodward gave certain rules for correlating wavelength of maximum absorption ( λmax ) with molecular structure . In 1959 Louis Fredrick Fieser modified these rules with more experimental data and the modified rule is known as Woodward_Fieser R ules. Woodward rules work well for dienes and polyenes with upto 4-double bonds or less . These sets of rules to calculate the wavelength of maximum absorption ( λmax ) of a compound in the ultraviolet-visible spectrum, based empirically have been called the Woodward_Fieser R ules or Woodward’s Rules. This may be differs from observed value by 4-5nm . 4

5. BASIC TERMINOLOGIES Homoannular diene Heteroannular diene Endocyclic double bond Exocyclic double bond Double bond extending conjugation A B 5

6. A) WOODWARD_FIESER RULE FOR CONJUGATED DIENES AND TRIENES Conjugated diene : Organic compound containing two or more double bonds each separated from other by a single bond. Base/Parent value: It means that each type of diene or triene system is having a certain fixed values 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 base value to obtain λmax for a particular compound. Longer the conjugated system greater the wavelength of absorption maximum.   According to Woodward’s rules the λmax of the molecule can be calculated using a formula:   λmax = Base value + Σ Substituent Contributions + Σ Other Contributions 6

7. Table A: Parent values and increments for different substituents /groups for calculating maximum wavelength Conjugated dienes correlations Standard (nm ) (A) Parent value Homo-annular conjugated dienes 253 Hetero-annular conjugated dienes 214 Butadiene system or a cyclic conjugated dienes 217 Acyclic trienes 245 7

8. (B) Increment for each substituent Standard (nm) Alkyl substituent or ring residue 5 Exocyclic double bond 5 Double bond extending conjugation 30 (C) Auxochrome Standard (nm) –OCOCH 3 – Cl ,-Br 5 –OR 6 –SR 30 –NR 2 60 8

9. Example 1: Solution:   Base value for Heteroannular conjugated diene = 214 nm 3 Ring residues (3 × 5 ) = 15 nm 1 Exocyclic double bond = 5 nm λmax = 234 nm 9

10. Example 2: Solution: Base value for Homoannular conjugated Diene = 253 nm 3 Ring residues (3 × 5) = 15 nm 1 Exocylic double bond = 5 nm λmax = 273 nm 10

11. Example 3: Solution: Base value for Heteroannular conjugated diene = 214 nm 3 Ring residues (3 × 5) = 15 nm 1 Exocyclic double bond = 5 nm λmax = 234 nm 11

12. Example 4: Solution : Base value for Heteroannular conjugated diene = 214 nm 3 Ring residues (3 × 5 ) = 15 nm 1 Exocyclic double bond = 5 nm -OR ( Alkoxy group) = 6 nm λmax = 240 nm 12

13. Example 5: Solution:   Base value for Homoannular conjugated diene = 253 nm 1 Alkyl substituent = 5 nm 3 Ring residues (3 × 5) = 15 nm 1 Exocyclic double bond = 5 nm λmax = 278 nm 13

14. Example 6: Solution:   Base value for Homoannular conjugated diene = 253 nm 5 Ring residues (5 × 5) = 25 nm 2 Double bond extending conjugation (2 × 30) = 60 nm 3 Exocyclic double bond (3 × 5) = 15 nm -OCOCH3 = 0 nm λmax = 353 nm 14

15. B) WOODWARD_FIESER RULE FOR CYCLIC DIENES (or AROMATIC COMPOUNDS) Like Woodward fieser rules, Scott devised a set of rules for calculating the absorption maximum for the derivatives of Acyl benzenes. These rules help in estimating the position of absorption maximum ( λmax ) in ethanol in a number of mono substituted aromatic ketones , aldehydes, acids, and esters. 15

16. Basic values Standard (nm) Ar COR 246 Ar CHO 250 Ar CO 2 H or Ar CO 2 R 230 Increments Alkyl groups or ring residues at ortho or meta positions 3 Alkyl groups or ring residues at Para positions 10 Table B: Parent values and increments for different substituents/groups for calculating maximum wavelength 16

17. Values for substituents or groups: Auxochromes Ortho position(nm) Meta position(nm) Para position(nm) -OH 7 7 25 -OCH3 7 7 25 - O( Oxonium ) 11 20 78 - Cl 10 -Br 2 2 15 -NH2 13 13 58 -NHCOCH3 20 20 45 -N(CH3)2 20 20 85 17

18. Example 1: Solution:   Base value for Aromatic ketone = 246 nm Hydroxyl group at meta position = 7 nm Hydroxyl group at para position = 25 nm λmax = 278 nm 18

19. Example 2: Solution: Base value for Ar -COOH = 230 nm Hydroxyl groups at meta positions (2 × 7) = 14 nm Hydroxyl group at para position = 25 nm λmax = 269 nm 19

20. Example 3: Solution: Base value = 246 nm Ring residue = 3 nm - OCH 3 at meta position = 7 nm λmax = 256 nm 20

21. C) WOODWARD-FIESER RULE FOR α , β -UNSATURATED CARBONYL COMPOUNDS (ENONES) Woodward and F ieser framed certain empirical rules for estimating the absorption maximum for α , β -unsaturated carbonyl compounds. The rules later modified by Scott . 21

22. Table C: Parent values and increments for different substituents/groups for calculating maximum wavelength 22

23. Values for substituents or groups: Auxochromes α - β - γ - δ - or higher -OH 35 30 - 50 -OR 35 30 17 31 - OAc 6 6 6 6 - Cl 15 12 - - -Br 25 30 - - -SR - 85 - - -NR 2 - 95 - - 23

24. Example 1: Solution: α , β-unsaturated acyclic ketone = 215 nm 2 alkyl groups at β -position (2 × 12) = 24 nm λmax = 239 nm 24

25. Example 2: Solution: Base value for α, β-unsaturated six membered ring ketone = 214 nm β- ring residue (1 × 12) = 12 nm δ- ring residue (1 × 18) = 18 nm 1 Double bond extending Conjugation (1 × 30) = 30 nm 1 Exocyclic double bond = 5 nm λmax = 279 nm 25

26. Example 3: Solution: Base value for α, β-unsaturated six membered ring ketone = 215 nm Substitution of alkyl groups at α - position = 10 nm Ring residue at β - position = 12 nm λmax = 237 nm 26

27. Example 4: Solution: Basic value = 215 nm 2 β ring residue (2 × 12) = 24 nm 1Exocylic double bonds = 5 nm λmax = 244 nm 27

28. Example 5: Solution: Basic value = 215 nm ά-ring residue = 10 nm δ-ring residue = 18 nm 1 Exocylic double bond = 5 nm 1Homoannular conjugated diene = 39 nm 1 Double bond extending conjugation = 30 nm λmax = 317 nm 28

29. Example 6: Solution: Cyclic enone = 215 nm 1 Double bond extending Conjugation = 30 nm β-ring residue = 12 nm δ-ring residue = 18 nm 1 Exocylic double bond = 5 nm λmax = 280 nm  29

30. Example 7: Five- membered enone = 202 nm 2 β-Ring residue (2 × 12) = 24 nm 1 Exocyclic double bond = 5 nm λmax = 231 nm Solution: 30

31. FIESER-KUHN RULE If the number of conjugated double bonds is more than 4, the W oodward and F ieser rules may not be applicable and hence F ieser with K uhn has derived an equation for predicting the λmax . M = No. of alkyl substitutents N = No. of conjugated double bonds Rendo = No. of rings with endocyclic double bonds Rexo = No. of rings with exocyclic double bonds   λmax = 114 + 5(M) + n(48-1.7n) - 16.5 Rendo - 10 Rexo 31

32. Examples:1 Solution: No. of alkyl substituents = 10 No. of rings with endocyclic double bond =2 λmax = 114+5(M) + n(48-1.7n) -16.5 Rendo -10 Rexo λmax = 114 + 5(10) +11(48-1.7 × 11) - (16.5 × 2) - (10 × 0) = 453.3 nm 32

33. POINTS TO REMEMBER In case for which both types of diene systems are present then the one with the longer wavelength is designated as a parent system. Whenever there is an increasing conjugation leads to increase in wavelength and requires less amount of energy. Up to four conjugations, Woodward_Fieser rule is applied. > Four conjugations , Fieser_Kuhn rule is applied. 33

34. REFRENCES Donald L. Pavia, Gary M. Lampman , George S. Kriz , “ Spectroscopy”, published by Cengage Learning, 2010. Pp. (379-387) SHARMA Y.R., “Elementary Organic Spectroscopy”, published by S. Chand & Company Ltd. 1 st edition, 2006. Pp. (31-49) CHATWAL G.R., ANAND S.K., “Instrumental Methods Of Chemical Analysis”, published by Himalaya Publishing House, 5 th edition, 2008. Pp. ( 2.162- 2.167) KALSI P.S., “A Text Book Of Organic Spectroscopy”, published by NEW AGE INTERNATIONAL PUBLISHERS, 6 th edition. 2007. Pp. ( 40 )   RAJASHEKARAN, “A Text Book Of UV-Visible a nd Infrared Spectroscopy”, Pp. (88-100) 34

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