UV/Vis Spectroscopy

Woodward's Rules for Conjugated Carbonyl Compounds

Woodward's Rules for Conjugated Carbonyl Compounds
Base values:
  X = R
       Six-membered ring or acyclic parent enone l=215 nm
       Five-membered ring parent enone l=202 nm
  X = H l=208 nm
  X = OH, OR l=195 nm
Increments for:
  Double bond extending conjugation 30
  Exocyclic double bond   5
  Endocyclic double bond in a 5- or 7-membered ring for X = OH, OR   5
  Homocyclic diene component 39
  Alkyl substituent or ring residue a 10
  b 12
  g or higher 18
Polar groupings:
  -OH a 35
  b 30
  d 50
  -OC(O)CH3 a,b,g,d   6
  -OCH3 a 35
  b 30
  g 17
  d 31
  -Cl a 15
  b,g,d 12
  -Br b 30
  a,g,d 25
  -NR2 b 95
Solvent correction*: variable
  lmax (calc'd) total

*Solvent shifts for various solvents:

Solvent

lmax shift (nm)
water + 8
chloroform - 1
ether - 7
cyclohexane - 11
dioxane - 5
hexane - 11

Example 1:

Acyclic enone:   215 nm
a-Alkyl groups or ring residues:   10 nm
b-Alkyl groups or ring residues: 2 x 12 = 24 nm
Calculated:   249 nm
Observed:   249 nm

Example 2:

Five-membered ring parent enone:   202 nm
b-Alkyl groups or ring residues: 2 x 12 = 24 nm
Exocyclic double bond:   5 nm
Calculated:   231 nm
Observed:   226 nm

Example 3:

Six-membered ring or alicyclic parent enone:   215 nm
Extended conjugation:   30 nm
Homocyclic diene component:   39 nm
d-Alkyl groups or ring residues:   18 nm
Calculated:   302 nm
Observed:   300 nm

Example 4:

Five-membered ring parent enone:   202 nm
a-Br:   25 nm
b-Alkyl groups or ring residues: 2 x 12 = 24 nm
Exocyclic double bond:   5 nm
Calculated:   256 nm
Observed:   251 nm

Example 5:

Carboxylic acid:   195 nm
a-Alkyl groups or ring residues:   10 nm
b-Alkyl groups or ring residues:   12 nm
Calculated:   217 nm
Observed:   217 nm

Example 6:

Ester:   195 nm
a-Alkyl groups or ring residues:   10 nm
b-Alkyl groups or ring residues:   12 nm
Endocyclic double bond in 7-membered ring:   5 nm
Calculated:   222 nm
Observed:   222 nm

Example 7:

Aldehyde:   208 nm
a-Alkyl groups or ring residues:   10 nm
b-Alkyl groups or ring residues: 2 x 12 = 24 nm
Calculated:   242 nm
Observed:   242 nm

Example 8:

Aldehyde:   208 nm
Extended conjugation:   30 nm
Homodiene component:   39 nm
a-Alkyl groups or ring residues:   10 nm
d-Alkyl groups or ring residues:   18 nm
Calculated:   304 nm
Observed:   302 nm

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