How to use a spectrometer?


The Woodward & Fieser rules allow to predict the absorption maximum’s wavelength of conjugated systems.

They apply in systems where π and σ bonds alternate.

To calculate the value of the absorption maximum’s wavelength, the bases are:

215 nm for heteroannular dienes:
252 nm for homoannular dienes (or cissoids):

A certain number of increments are added according to the substituents of the molecule:
  -R (alkyl radical) + 5 nm
  -OR (alcoxy radical) + 6 nm
  -X (-Cl, -Br, -halogen) + 10 nm
  -OC(O)R (acyloxy, ether) + 0 nm
  -SR (sulfur) + 30 nm
  -NR2 (amine) + 60 nm
  – C=C (double conjugated bond) + 30 nm
  – C6H5 (phenyl radical) + 60 nm
  -C=C (exocyclical double bond) + 5 nm
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