Additivity Rules for π-π* Transitions of Enones


Base Values:
Acylic ketones: 215 nm
6-membered cylic: 215 nm
5-membered cylic: 202 nm
Aldehydes: 210 nm
Carboxylic acids and esters: 195 nm
Alkyl Groups:
α +10 nm
β +12 nm
γ +18 nm
Polar Groups, -OH:
α +35 nm
β +30 nm
α +15 nm
β +12 nm
Double bond extending conjugation +30 nm
For example:

Reference: R.M. Silverstein, G.C. Bassler, and T.C. Morrill, "Spectrometric Identification of Organic Compounds," 5th ed., Wiley, NY, 199l, pps. 302-303.