Review of Spectroscopic Methods I

Review of Spectroscopic Methods I -...

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    Quick Review of Spectroscopic  Methods. Overview of IR and NMR.
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Electromagnetic Energy and Molecular  Interaction Vacuum UV:  σ  (sigma) bond excitation. UV-Vis: π  (pi) electron, lone pair, or d orbital  electron excitation. IR: bond vibration, molecular bending, etc  excitation. Microwave: molecular rotations. Radiowaves: nuclear spin transitions.
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IR-Absorbance Frequency of motion must match frequency of  energy. Example:  C O Bond Stretchng wavenumber ~ 1710 cm -1 IR absorbed ~ 1710 cm -1
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IR - Strength of Absorbance: Polarity of the molecular fragment in  motion. Magnitude of the change on dipole moment  with the motion. If the motion does not cause a change in  the dipole there will not be absorbance  even if the fragment is extremely polar.
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Factors that affect the frequency of  absorbance. Bond Strength  (force constant).  A  stronger bond  vibrates at a higher  frequency than a  weaker bond. C C C C C C C N C N C N 1200 cm -1 1100 cm -1 1670 cm -1 2200 cm -1 1660 cm -1 2100 cm -1
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absorbance. Masses of the  atoms involved.   Lighter atoms  move with greater  speed for the same  energy than do  heavier atoms. C
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This note was uploaded on 12/05/2010 for the course CHM 238 taught by Professor Arney during the Spring '07 term at Sam Houston State University.

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Review of Spectroscopic Methods I -...

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