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I. Spectroscopy

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I. Spectroscopy. Study of the interaction of electromagnetic ... not just visible light!! http://www.dnr.sc.gov/ael/personals/pjpb/lecture/spectrum.gif ... – PowerPoint PPT presentation

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Title: I. Spectroscopy


1
I. Spectroscopy
  • Study of the interaction of electromagnetic
    radiation (light)
  • with molecules

A. Electromagnetic Radiation
- not just visible light!!
http//www.dnr.sc.gov/ael/personals/pjpb/lecture/s
pectrum.gif
2
1. Wave Behavior of Light
a. Wavelength (?)
  • often given in cm or nm

b. Frequency (?)
  • of wave cycles that pass a point in a second
  • s-1

3
2. Particle Behavior
a. Photon massless packet of energy
b. A little bit of math!
  • First c ??, where c is the speed of light
  • (3.00 x 108 m s-1)
  • ? h? , where h is Plancks Constant
  • since we know that ? c/?
  • then we also know that ? hc/?
  • So??
  • this means that the energy of the light is
    directly
  • proportional to the frequency
  • energy of light is inversely proportional to
    wavelength

4
3. Absorption
  • light of particular energy can be absorbed by a
    molecule
  • resulting in the molecule adopting an excited
    state
  • - this absorption can be measured!!

5
B. Infrared (IR) Spectroscopy
  • Upon absorption of light in the infrared region
    of the
  • electromagnetic spectrum by organic molecules
  • results in molecular motion

1. Types of Motion
6
2. What we observe
  • data is recorded using wavenumbers ( ) where
  • 1/?, (cm-1)
  • this means energy is directly proportional to
  • wavenumber, i.e. higher wavenumber, higher
    energy
  • can think of as weights on springs

a. Effect of Atom Type
C(sp3) H 2960 - 2850 cm-1 O
 H (alcohol) 3600 - 3200 cm-1
b. Effect of Bond Strength
CC 1680 - 1620 cm-1 CC 2260 - 2100 cm-1
7
3. Sample Spectrum
8
4. Table of IR Data
9
5. Trends
a. Hydrogen Region 3330 - 2700 cm-1
O H(alc) 3650 - 3200 cm-1 O H(CA) 3300 -
2500 cm-1 N H(amine) 3500 - 3250 cm-1 N
H(amide) 3500 - 3400 cm-1
C(sp3) H 2960 - 2850 cm-1 C(sp2) H 3150 -
3050 cm-1 C(sp) H 3300 cm-1
b. Triple Bond Region 2300 - 2000 cm-1
CC(alkyne) 2260 - 2100 cm-1 CN(nitrile)
2260 - 2220 cm-1
c. Double Bond Region 1900 - 1500 cm-1
C O(ald) 1740 - 1690 cm-1 C O(ket) 1750 -
1680 cm-1 C O(est) 1750 - 1735 cm-1
C O(CA) 1760 - 1710 cm-1 C O(am) 1690 - 1630
cm-1 C C 1680 - 1620 cm-1
10
5. Trends
d. Fingerprint Region
- Not much information, except!! C(sp2, aromatic,
bending) H Mono-substituted 770 - 730, 720 -
680 cm-1 Di-substituted (ortho) 770 - 735
cm-1 Di-substituted (meta) 810 - 750
cm-1 Di-substituted (para) 860 - 800 cm-1
11
II. Sample Spectra
A. Spectrum 1
  • strong versus medium versus weak Why?
  • Dipole moment of molecule must change as
    vibration occurs
  • Number of bonds absorbing

12
B. Spectrum 2
  • Sharp versus Broad Signals Why?
  • multiple rotational energy levels in each
    vibrational energy level
  • ??

13
Multiple Rotational Energy Levels??
14
C. Spectrum 3 What functional groups are
present?
15
D. Spectrum 4 What functional groups are
present?
16
E. Spectrum 5 What functional groups are
present?
17
F. Spectrum 6 Propose a structure for
a compound with MF C7H12O
18
G. Spectrum 7 Propose a structure for
a compound with MF C5H12O
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