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

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

An IR Spectrum

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, 4000-625 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.

Vibrational Modes of Bonds

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

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

IR spectrum of hexanoic acid

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)