Organic Chemistry Reviews Organic Spectroscopy (IR and NMR)

1. Organic Chemistry ReviewsOrganic Spectroscopy (IR and NMR) Cindy Boulton January 24, 2010

2. Electromagnetic Radiation Basics • Electromagnetic Spectrum • X-rays ->UV ->Visible Light ->IR ->Microwaves ->Radiowaves • X-rays: high energy, high frequency, short wavelength • Radiowaves: low energy, low frequency, long wavelength • c = λν • c: speed of light (3 x 108 m/sec) • λ: wavelength • ν: frequency • E = hν • E: Energy • h: Plank’s Constant (6.626 x 10-34 m2kg/sec) • ν: frequency

3. Spectroscopy • UV/Vis Spectroscopy • Identify number of π bonds in a molecule • Not much detail • IR Spectroscopy • Identify the functional groups present in a molecule • Absorption of infrared radiation • NMR Spectroscopy • C13 or H1 • Nuclear Magnetic Residence • Identify the structure of a molecule • Absorption of radiowaves

4. Infrared (IR) Spectroscopy • Identify functional groups • Light source • Wavelength below red • Monochrometer • Select wavelength of light source • Dial to select a range of wavelengths over time • Sample • Absorb light • Detector • Identifies new wavelength • Read out device • Peaks tell which functional groups in the sample

5. The Spectrum • X-axis: Light wavelength (cm-1 ) from 4000-600 • Y-axis: Percent Transmission (% T) from 0-100 • How much of the wavelength got through • Baseline at 100% for when no functional group detected at wavelength • Functional Groups • 4000-1500 • Fingerprint Region • 1400-600 • Specific for each molecule

6. Molecular Vibrations • What in the molecule absorbs the IR radiation? • At the specific frequency for a bond, the bond will contrast and expand • Each bond has a different frequency • Tells what bonds are in a molecule, which functional groups • Dipole • Polar bond • Must change net dipole for there to be IR absorption

7. Functional Groups • Alkane (C-H) • Long, jagged peak below 3000 • Hydroxyl (-O-H) • Big, broad peak at 3300 • Aromatic (Ar-H) Ring • Long, jagged peak above 3000 • Carbonyl (C=O) • Long, sharp peak at 1700 • Carboxyl • Broad, jagged peak from 3300-3000 for –O-H and C-H • Long, sharp peak at 1700 for C=O

8. Substituted Benzene • Overtones • “Saw tooth” small peaks at 1800 • Substituded • Group attach to ring, identify location • 800-600 region • Monosubstituded • One group attached • Two peaks close together like snake fangs

9. Substituted Benzene cont. • Disubstituted Benzene • Two groups attached • Ortho- (1,2) • One peak closer to 600 • Meta- (1,3) • Two peaks spread apart, Vampire • Para- (1,4) • One peak closer to 800

10. Amines • N-H • Shallow peak at 3500 • Primary • 1 Carbon attached and 2 Hydrogens attached • 2 peaks • Secondary • 2 Carbons attached and 1 Hydrogen attached • 1 peak • Tertiary • 3 Carbons attached • No peak • No Hydrogens, (N-H) • Weak peaks can be lost by something stronger (-O-H)

11. Alkynes • Small peak at 2100 • Terminal Alkyne • Sharp peak at 3300 • Symmetrical vs. Not Symmetrical • The less symmetrical the alkyne is the great the dipole change and greater the peak at 2100