Interpretation of Spectra

Interpretation of Spectra

1. Identification of compound

   • Similar to atomic spectra
     • Particular wavelength/energy

2. Wavelength tables

   • Particular range of wavelength/energy
     • Range as interacting wavelength slightly effected by rest of molecule
   • Interaction of
     • Particular bonds
     • Particular functional groups

3. Identifying compound by functional group (s)

4. UV/Vis

   • Table of absorbance wavelengths
   • Bonds interact at absorbed wavelengths
   • Final column
     • Specific electron excitation (transition)
       • n
       • σ - involved with single bonds- strongest bonds
       • π - bond more than one bond or bonding pair of electron and float around the signma therefore is weaker.
   • Star means its excited
   • Wavelengths are a guide – peaks may be broad & alter slightly depending on experimental conditions
   • Analyse big peak as can much more confidently analyse as the absrobance is so much greater.

5. FTIR

   • Comparison tables
   • Infra red radiation
     • Polychromatic
     • Compound absorbs wavelengths
       • Often wavenumber
         • [1/wavelength = wavenumber (cm-1)]
     • Wavelengths relate to functional groups
   • Transmitted EMR analysed
     • Determines wavelength(s) absorbed
       • Troughs in spectra (absorbance)
     • Spectra of transmittance
   • Method same but instead of using wavelength use wavenumber
   • Correlation table
     • Shaded bands
     • Wavenumber range- functional groups absorbed
     • Position in range depends on molecular environment
   • FTIR identification of structures
     • Look at single bonds
     • Bond combinations
     • Multiple compounds
     • Shifts used to identify GBH

6. Complex structure- complex spectra

   • Functional groups can have multiple absorbance wavelengths
   • More parts of compound can absorb
   • useful qualitative technique

7. To determine functional groups, compare absorbance to absorbance data tables.

8. Produce expected data table of absorbance troughs