Ch 11 Ochem Spectroscopy

Ch 11 Ochem Spectroscopy

1. 1.1 Infared Spectroscopy

   • Intramolecular Vibrations and rotations
     • wavenumber to measure
     • v. complex is in 400-1500cm-1 range
       • fingerprint region
   • Characteristic Absorptions
     • important ones
       • O-H
         • wide 3300
           • alcohol
           • N-H is sharp
         • wide 3000
           • Carboxylic acid
       • Carbonyl C=O
         • 1700 sharp deep
     • increases with addition of atoms and H
     • measured as percent transmittance
       • amount of light that passes through to detector
   • bond streching bending and other conformations
   • can help find functional groups

2. 11.2 Ultraviolet Spectroscopy

   • Electron Transitions
     • pi-electrons or nonbonding electrons can be excited
       • these go to higher levels
       • v. excitable with a lower gap between HOMO and LUMO
         • absorb longer wavelengths with less energy
   • Conjugated systems
     • can be excited
     • create higher maximum wavelengths
     • can sometimes create visible color
     • AKA UV-Vis
   • send UV light through dissolved sample
     • measure absorbance and compare to wavelength
       • absorbance is created by electric transitions

3. 11.3 Nuclear magnetic Resonance Spectroscopy

   • Proton NMR
     • if H cemically equivlent creates larger line
       • INTEGRATION
     • If atoms deshielded
       • electron density is pulled away
         • Cannot shield itself from magnetic
           • goes downfield
     • splitting
       • when hydrogens near they create more combos
         • if in different energy states, then other Hy will have more possible results
           • n+1 rule
             • does not include H attached to O or N
               • measured with J= coupling constant
       • AKA spin-spin coupling
     • important values
       • aldehyde at 9-10
       • carboxylic acid 10.5-12
       • aromatic 6-8.5
       • SP3 carbons 0-3.0
       • Sp2 carbon 4.6-6.0
       • Sp carbons 2-3.0
   • try to excite lower energy Alpha to beta
     • use magnetic field
       • create a frequency depending on atoms own field and environment
   • Measured in PPM
     • increases to he left= downfield
     • TMS (tetramethylsilane) is used to calebrate 0
   • measures the alignment spin of a nucleus
     • helps find backbone of e-

4. measures the energy differences of different free states

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