Anderson University

1
UV/Visible Spectroscopy

• Anderson University

2
Electromagnetic Spectrum
frequency (n)
high
low
energy
X-Ray Ultraviolet
infrared micro radio

wave wave
visible
ultraviolet
wavelength (l)
short
long
3
(No Transcript)
4
If a compound absorbs one color, we see its
complementary color.
5
Principles of UV-Visible Spectroscopy
Chromophores - groups of atoms responsible for
these transitions
6
UV Visible Spectrum
lmax
UV/visible bands are broad due to overlap of
rotational and vibrational states of a molecule.
A
Wavelength in nm (l)
7
Solvents and Cells for UV Spectroscopy
solvent
Sample cell
200 nm
400 nm
800 nm
uv
visible
Glass or plastic
quartz
8
Common Chromophores Alkenes
?
E
165 nm
? 15,000
?
9
Common ChromophoresCarbonyl Compounds
?
E
n
?
10
Possible transitions
11
Conjugation
Alternate single and double bonds overlap of
p-orbitals
Conjugation lowers energy of ? ? ? transition
12
1,3-butadiene
antibonding
bonding
13
UV Absorption of Conjugated Alkenes

• Increasing conjugation gives
• longer wavelength absorption
• more intense absorption

14
b-Carotene
11 double bonds
lmax 460 nm
Lycopene
11 conjugated double bonds, 13 total
lmax 474 nm
15
(No Transcript)
16
If a compound absorbs one color, we see its
complementary color.
17
Heme Metabolism
Bilirubin is normally metabolized in the liver to
a water soluble derivative that is eliminated in
the bile. Some infants or individuals with a
genetic disorder lack the enzyme that produces
this derivative and develop jaundice. Buildup of
bilirubin leads to brain damage.
18
Bilirubin
Nonpolar not excreted
19
Photoenolization
polar
nonpolar
BR-albumin
BR
BR
light
bile
PBR-albumin
PBR
PBR
skin
blood
liver
20
UV-Vis

• Which would absorb a longer wavelength of light,
  1,4-pentadiene or 1,3-pentadiene?

Conjugated
Isolated
178 nm
223 nm