Ultraviolet-Visible (UV-Vis) Spectroscopy – Sample Problems Using Woodward-Fieser Rules

Introduction

In this page we discuss a few examples of how we can utilize the Woodward-Fieser rules to determine the wavelength of maximum absorption for some molecules. We highly recommend that you read up the first two sections on the Woodward rules to calculate the λmax for conjugated dienes and the Woodward rules to calculate the λmax for unsaturated carbonyl compounds, before you read this page.

Note: Numerical values for Woodward-Fieser rules differ slightly from one textbook to another. We have tried to compile an extensive list of numerical values from online resources, textbooks and journal articles based on the popularity of the number. It is recommended that you learn on how to apply the values for the contributors and then follow the values given in a text book recommended by your teacher, or use our values. We believe that learning how to apply the rules is more essential than actually getting the exact answer. Other’s opinions may vary.

In these sample problems you will be shown the structure, then the structure is highlighted to show you key features which would affect the λmax of the molecule. Then the table will show you the solutions on how to solve to get the wavelength of maximum absorption, with a final calculated λmax using the Woodward-Fieser rules. In some cases if we have an observed λmax for comparison, it may be given as well.

Note- If you have your own problems please write the IUPAC name in the comments section and I will attempt to solve it and add it to this list of examples.

Example/Sample Problem 1

2,4-dimethylpenta-1,3-diene 2,4-dimethylpenta-1,3-diene solution using Woodward theorem
Name of Compound 2,4-dimethylpenta-1,3-diene
Woodward Component Contribution
Core- Transoid/Heteroannular Diene + 215 nm
Substituents- 3 alkyl groups 3 x 5 = + 15 nm
Other Effects 0
Calculated λmax 230 nm
Observed λmax 234 nm

Example/Sample Problem 2

1-methylcyclohexa-1,3-diene 1-methylcyclohexa-1,3-diene solution using Woodward Theorem
Name of Compound 1-methylcyclohexa-1,3-diene
Woodward Component Contribution
Core- Cisoid/Homoannular Diene + 253 nm
Substituents- 3 alkyl groups 3 x 5 = + 15 nm
Other Effects 0
Calculated λmax 268 nm
Observed λmax N/A

Example/Sample Problem 3

Steroidal Molecule Steroidal Molecule solved using Woodward-Fieser rules
Name of Compound 3-methoxy-10-methyl-2,7,8,9,10,11,12,13,14,15,16,17-dodecahydro-1H-cyclopenta[a]phenanthrene
Woodward Component Contribution
Core- Transoid/Heteroannular Diene + 215 nm
Substituents- 3 alkyl groups

1 alkoxy group

3 x 5 = + 15 nm

+ 6 nm

Other Effects- Exocyclic Double Bond + 5 nm
Calculated λmax 241 nm
Observed λmax N/A

Example/Sample Problem 4

Steroidal diene structure Steroidal diene structure solved using Woodward-Fieser rules
Name of Compound 10,13-dimethyl-2,3,9,10,11,12,13,15,16,17-decahydro-1H-cyclopenta[a]phenanthrene
Woodward Component Contribution
Core- Transoid/Heteroannular + 215 nm
Substituents- 5 alkyl groups

1 Double bond extending conjugation

5 x 5 = + 25 nm

+ 30 nm

Other Effects- 3 Exocyclic Double Bond + 15 nm
Calculated λmax 285 nm
Observed λmax 283 nm

Example/Sample Problem 5

Steroid containing homoannular and heteroannular double bondNote- In this example the molecule contains both, a homoannular diene system and a heteroannular diene system. In such a molecule the core chromophore is considered to be the homoannular system and accordingly the calculations are performed.

Homoannular system

Steroid containing homoannular and heteroannular double bond solution 1 using homoannular core
Component Contribution
Core- Homoannular/Cisoid diene + 253 nm
Substituents- 5 alkyl substituents

Double bond extending conjugation

5 x 5 = + 25 nm

+ 30 nm

Other Effects- 3 Exocyclic double bonds 3 x 5 = + 15 nm
Calculated λmax 323 nm
Observed λmax n/a

Example/Sample Problem 6

3,4-dimethylpent-3-en-2-one an alpha,beta-unsaturated ketone 3,4-dimethylpent-3-en-2-one an alpha,beta-unsaturated ketone solved using Woodward-Fieser rules
Name of Compound 3,4-dimethylpent-3-en-2-one
Component Contribution
Core- α,β-unsaturated ketone + 215 nm
Substituents at α-position- 1 alkyl group + 10 nm
Substituents at β-position- 2 alkyl groups 2 x 12 = 24 nm
Other Effects 0
Calculated λmax 249 nm
Observed λmax 249 nm

Example/Sample Problem 7

1-methyl-4,5,6,7,8,8a-hexahydroazulen-2(1H)-one alpha,beta-unsaturated cyclopentenone derivative 1-methyl-4,5,6,7,8,8a-hexahydroazulen-2(1H)-one alpha,beta-unsaturated cyclopentenone derivative solved using Woodward Theorem
Name of Compound 1-methyl-4,5,6,7,8,8a-hexahydroazulen-2(1H)-one
Component Contribution
Core- cyclopentenone + 202 nm
Substituents at α-position 0
Substituents at β-position- 2 alkyl groups 2 x 12= + 24 nm
Other Effects- 1 Exocyclic Double Bond + 5 nm
Calculated λmax 231 nm
Observed λmax 226 nm

Example/Sample Problem 8

4,4a,5,6,7,8-hexahydrophenanthren-2(3H)-one steroidal ketone 4,4a,5,6,7,8-hexahydrophenanthren-2(3H)-one steroidal ketone solved using Woodward-Fieser Rules
Name of Compound 4,4a,5,6,7,8-hexahydrophenanthren-2(3H)-one
Component Contribution
Core- cyclohexenone + 215 nm
Substituents at α-position: 0
Substituents at β-position: 1 alkyl group + 12 nm
Substituents at γ-position: 0
Substituents at δ-position: 0
Substituents at ε-position: 1 alkyl group + 18 nm
Substituents at ζ-position: 2 alkyl group 2 x 18 = + 36 nm
Other Effects: 2 Double bonds extending conjugation

Homoannular Diene system in ring B

1 Exocyclic double bond

2 x 30 = + 60 nm

+ 35 nm

+ 5 nm

Calculated λmax 381 nm
Observed λmax 388 nm

Note- If you have your own problems please write the IUPAC name in the comments section and I will attempt to solve it and add it to this list of examples.

Example/Sample Problems For β-Carotene and all-trans-lycophene

β-Carotene and lycophene are polyenes with more than 4 double bonds, and hence their calculations cannot be done using the Woodward rules. In order to calculate their λmax you must use the Fieser-Kuhn rules. Check out this post on the Fieser-Kuhn Rules to Calculate Wavelength of Maximum Absorption (Lambda-max) of Polyenes (with Sample Problems) for the solution of these problems.

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