1. Lecture 10 IR Theory This Week In Lab: Ch 6 PreLab Due
Ch 6: Procedure 1 & Procedure 2 (if time)
Quiz 3
Next Week in Lab:
Ch 6: Procedures 2-4
Ch 5 Final Report Due

2. Spectroscopy NMR (Nuclear Magnetic Resonance Spectroscopy):
Uses radio waves (electromagnetic radiation)
Interacts with sample’s nuclei in the presence of a magnet
Effect: nuclei flip and relax (known as resonance)
1H NMR:
Determine bond connectivities/pieces of a structure, whole structure
IR (Infrared Spectroscopy)
IR radiation
Interacts with molecule as a whole
Effect: bond vibrations within molecule
IR Use:
Determine the functional groups present in a structure:
-OH, C=O, C-O, NH2, C=C, CC, C=N, CN

3. An IR Spectrum

4. IR Spectroscopy
Main Use: To detect the presence or absence of a functional group (specific
bonds) in a molecule
How It Works:
Bonds vibrate freely at specific wavelengths (wavenumbers)
Want to cause the bonds to increase the magnitude of this vibrational
frequency
Subject compound to IR radiation, cm-1
cm-1 is the unit for wavenumber (n) (The numbers of waves within 1 cm)
n is directly proportional to energy (unlike wavelength)
4. Bonds absorb energy equal to their natural vibrational energy - it is
quantized. This absorption of energy causes a change in dipole moment
for the bond.
5. Upon absorption, bonds stretch and/or bend; the IR measures this
absorption.

5. Vibrational Modes of Bonds

6. Correlation Chart
Specific bonds absorb specific IR radiation and signals will appear within certain
wavenumber ranges (similar to NMR).

7. Correlation Chart
Specific bonds absorb specific IR radiation and signals will appear within certain
wavenumber ranges (similar to NMR).

8. IR spectrum of hexanoic acid

9. A: O-H stretch (strong, broad)
C: C-H stretch (strong, sharp)
E: CC or CN stretch (sharp)
F: C=O stretch (strong, medium to sharp)
G: C=C stretch (sharp)
J: C-O stretch (strong, medium)
K: C-X stretch (sharp)