This document discusses the Woodward-Fieser rules for predicting UV-Vis absorption maxima (λmax values) of α,β unsaturated carbonyl compounds. The basic λmax values are 215 nm for acyclic and six-membered cyclic ketones, and 202 nm for five-membered cyclic ketones. Increments are given for substituents on the α,β unsaturated carbonyl system, such as alkyl groups, hydroxyl groups, exocyclic and extended conjugated double bonds, and homoannular dienes. Examples are given to demonstrate how to use the increments to calculate λmax values.

1. MAHARAJAH’S COLLEGE (AUTONOMOUS)
VIZIANAGARAM
Estd.1879
Mr. S. TIRUMALA SANTHOSH KUMAR
ASSISTANT PROFESSOR IN CHEMISTRY
E-mail ID : san_sidhu@yahoo.com

2. PROBLEMS
ULTRA VOILET VISIBLE
SPECTROSCOPY

3. WOODWARD FIESER RULES
For
α,β Unsaturated Carbonyl compounds
• Acyclic or six membered cyclic α,β Unsaturated Ketone compounds
basic λmax value is --- 215 nm
Acyclic ketone compound Six membered cyclic ketone compound
• Five membered cyclic α,β Unsaturated Ketone compounds
basic λmax value is --- 202 nm
• Acyclic or cylic α,β Unsaturated Aldehyde compounds
basic λmax value is --- 207 nm
O
O
O
O

4. WOODWARD FIESER RULES
For
α,β Unsaturated Carbonyl compounds
Increments or substituents:
• Ring Residue or Alkyl substitute at each position of double bond;
•
• β position have one alkyl substituent - 12nm
• β position have one alkyl substituent - 12nm
δ position have one alkyl substituent -18nm
δ position have one -OH substituent - 50nm
O


O 

 OH


5. WOODWARD FIESER RULES
For
α,β Unsaturated Carbonyl compounds
• Exocyclic double bond basic value – 05nm
The double bond present in the out side of the ring with conjugation is called
Exocyclic double bond.
Only one exocyclic double bond No exocyclic One exocyclic
• Extended conjugated Double bond basic value : 30nm
The double bond is a part of the conjugation which is extension the
conjagated system.
One Extended double bond Only one extended Only one extended
double bond double bond
O 



A B
O 

A




B
O
O 



O 






6. WOODWARD FIESER RULES
For
α,β Unsaturated Carbonyl compounds
• Homoannular conjugated diene basic value – 39nm
The Conjugated double bonds present in the same ring is called Homoannular
Homo annular is present No Homoannular
O 





O 






7. WOODWARD FIESER RULES
For
α,β Unsaturated Carbonyl compounds
Examples:
1.
Acyclic α,β Unsaturated ketone compounds basic value – 215nm
Alkyle substitute at only δ position – 1 X 18 = 18nm
Extended conjugated double bond – 1 X 30 = 30nm
-----------------
λmax value = 263nm
------------------
2. cyclic α,β Unsaturated ketone compounds basic value – 215nm
Alkyle substitute at only β position – 1 X 12 = 12nm
Alkyle substitute at only δ position – 1 X 18 = 18nm
Exocyclic double bond – 1 X 05 = 05nm
Extended conjugated double bond – 2 X 30 = 60nm
Homoannular conjugated diene -- 1 X 39 = 39nm
-----------------
λmax value = 349nm
------------------
O


O 




