448
9 UV/Vis
Example: Estimation of the absorption maximum for
O
O
base value (homoannular)
253
1 additional conjugated double bond
30
1 exocyclic double bond
5
3 C-substituents
15
1 OCOCH 3
0
estimated
303
experimental
306
9.3.2 α,β-Unsaturated Carbonyl Compounds
The π π* transition of α,β-unsaturated carbonyl compounds is above ≈200 nm
with typical intensities of the order of log ε ≈ 4. Its position can be estimated with
the extended Woodward rule. For cross-conjugated systems, the value for the chromophore absorbing at the longest wavelength must be calculated.
Extended Woodward rule for estimating the position of the π π * transition
(λ max in nm)
O
X
α
β
γ
δ
Parent system
O
X
X: alkyl
X: H
X: OH
X: O–alkyl
215
207
193
193
O
215
O
202
9 UV/Vis
Example: Estimation of the absorption maximum for
O
O
base value (homoannular)
253
1 additional conjugated double bond
30
1 exocyclic double bond
5
3 C-substituents
15
1 OCOCH 3
0
estimated
303
experimental
306
9.3.2 α,β-Unsaturated Carbonyl Compounds
The π π* transition of α,β-unsaturated carbonyl compounds is above ≈200 nm
with typical intensities of the order of log ε ≈ 4. Its position can be estimated with
the extended Woodward rule. For cross-conjugated systems, the value for the chromophore absorbing at the longest wavelength must be calculated.
Extended Woodward rule for estimating the position of the π π * transition
(λ max in nm)
O
X
α
β
γ
δ
Parent system
O
X
X: alkyl
X: H
X: OH
X: O–alkyl
215
207
193
193
O
215
O
202