Invisible light

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Invisible light
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Pit Viper and Mosquitoes
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Synthetic Aperture Radar (SAR)
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X-Ray
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X-Ray backscatter
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X-Ray backscatter
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MRI
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MRI of brain
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MRI
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PET Scan
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NonHodgkins Lymphoma PET scan
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Lymphoma PET scan
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CAT Scan
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CAT scan
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Thermography
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Thermography
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Global Hawk Drone
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Stinger Missile
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Pit Viper and Mosquitoes
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UV/Visible Spectroscopy

• CHE 4100
• Anderson University

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

wave wave
visible
ultraviolet
wavelength (l)
short
long
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If a compound absorbs one color, we see its
complementary color.
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Principles of UV-Visible Spectroscopy
Chromophores - groups of atoms responsible for
these transitions
Forbidden transitions - less probable - low
intensity
Allowed transitions - more probable - high
intensity
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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)
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Transmittance and Absorbance
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Beers Law
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Beers Law
slope molar absorptivity
Molar concentration
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Solvents and Cells for UV Spectroscopy
solvent
Sample cell
200 nm
400 nm
800 nm
uv
visible
Glass or plastic
quartz
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Common Chromophores Alkenes
?
E
165 nm
? 15,000
?
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Common ChromophoresCarbonyl Compounds
?
E
n
?
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Possible transitions
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Conjugation
Alternate single and double bonds overlap of
p-orbitals
Conjugation lowers energy of ? ? ? transition
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1,3-butadiene
antibonding
bonding
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UV Absorption of Conjugated Alkenes

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

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b-Carotene
11 double bonds
lmax 460 nm (e 139,000)
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If a compound absorbs one color, we see its
complementary color.
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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.
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Bilirubin
Nonpolar not excreted
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Photoenolization
polar
nonpolar
BR-albumin
BR
BR
light
bile
PBR-albumin
PBR
PBR
skin
blood
liver
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UV-Vis

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

Conjugated
Isolated
178 nm
223 nm
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Fine structure is vibrational Fine structure.
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Robert Burns Woodward 1965 Nobel Prize in
Chemistry
First synthesized quinine, cholesterol and
cortisone (1951), chlorophyll (1960),
tetracycline (1962), Vitamin B12 (1971- Included
over 100 reactions), deduced structures For
penicillin (1945), strychnine (1947),
etc. Widely known as the father of modern
organic synthesis.
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Woodward-Fieser Rules for Dienes

• Base Value
• heteroannular 214 nm
• homoannular 253 nm
• Additions for
• alkyl group or ring residue 5 nm
• double bond extending conjugation 30 nm
• exocyclic double bond 5 nm

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Exocyclic/Endocyclic
endocylic
exocyclic
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Calculate the ?max for the following compounds
253 (base) 15 (3 ring residues) 5 (exocyclic
CC) ------------ 273 nm calc. Observed 275 nm
214 (base) 15 (3 ring residues) 5 (1
exocyclic CC) ----------- 234 nm calc. Observed
235 nm.
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Fieser-Kuhn rules
Used for conjugated systems with more than 4
double bonds.
l max 114 5M n(48.0-1.7n) 16.5Rendo
10Rexo
n number of conjugated double bonds M number
of alkyl or alkyl like substituents on the
conjugated system Rendo number of rings with
endocyclic double bonds in the conjugated
system Rexo number of rings with exocyclic
double bonds
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Lycopene
114 5(8) 1148.0 1.7(11) 0 0 476
nm Observed 474 nm (hexane)
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Carbonyl Compounds

• Saturated ketones and aldehydes
• Far-UV region
• - p -gt p 150 nm, strong
• n -gt s 190 nm, strong
• Near UV, 270-300 nm (n -gt p), weak

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Woodward Rules for Enones

• Base values
• acyclic or 6-membered ring 215 nm
• 5-membered ring 202 nm
• Additions for
• double bond extending conjugation 30 nm
• alkyl group or ring residue a 10 nm
• b 12 nm
• ? g 18 nm
• exocyclic double bond 5 nm

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1-Acetylcyclohexene

• 215 (base)
• 10 (a substituent)
• 12 (b substitutent)
• -----
• 237 nm
• Obs. 232 nm.

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Cholesta-1,4-dien-3-one

• 215 (base)
• 24 (2 b substituents)
• 5 (1 exocyclic CC)
• -----
• 244 nm
• Obs. 245 nm.

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Enol of 1,2-cyclopentanedione

• 202 (base)
• 12 (b substituent)
• 35 (a-OH)
• -----
• 249 nm
• Obs. 247 nm.

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Aromatic Compounds
Substituents shift 255 nm band to higher
wavelength
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Polyaromatics
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Substituent Effects on Aromatic Absorption
255 nm band is sensitive to electron density of
aromatic ring
Electron density Red highest Green moderate
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pH Effects on Aromatic Absorption
Phenoxide ion Electrostatic potential map
Anilinium ion Electrostatic potential map