UV-Vis Spectroscopy

http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/UV-Vis/spectrum.htm

Detector set at 240 nm

Detector set at 254 nm

Detector set at 280 nm

Area %Aspirin 19.5%Acetaminophen 50.0%Caffeine 20.5%

Area %Aspirin 7.3%Acetaminophen 81.9%Caffeine 10.8%

Area %Aspirin 24.8%Acetaminophen 39.3%Caffeine 35.9%

UV-Vis SpectroscopyHPLC: Peak Area vs Detector setting

Excedrin ES250 mg aspirin; 250 mg acetaminophen; 65 mg caffeine

Caffeine(1.6 x 10-3 g/L)max = 272 nm,

Abs. = 0.34

Aspirin(1.6 x 10-3 g/L)max = 296 nm,

Abs. = 0.18

Acetaminophen (1.6 x 10-3 g/L)max = 248 nm,

Abs. = 0.61

254 nm

280 nm

240 nm

UV-Vis Spectroscopy: max

UV-Vis Spectroscopy: max and molar absorbtivity (

Acetaminophen (1.6 x 10-3 g/L)max = 248 nm, Abs. = 0.61

Caffeine(1.6 x 10-3 g/L)max = 272 nm, Abs. = 0.34

UV-Vis Spectroscopy: Chromophores

http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/UV-Vis/spectrum.htm

Chromo-phore

Example Excitation λmax, nm ε Solvent

C=C Ethene π  __>   π* 171 15,000 hexane

C≡C 1-Hexyne π  __>   π* 180 10,000 hexane

C=O Ethanaln  __>  π*π  __>  π*

290180

1510,000

hexanehexane

N=ONitro-

methanen  __>  π*π  __>  π*

275200

175,000

ethanolethanol

C-X   X=BrX=I

Methyl bromideMethyl Iodide

n  __>  σ*n  __>  σ*

205255

200360

hexanehexane

UV-Vis: Chromophores

http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/UV-Vis/spectrum.htm

UV-Vis Spectroscopy: Chromophores

Table 7.3, p 362 Intro to Spectroscopy, 3rd ed., Pavia et al.

UV-Vis Spectroscopy: Solvents

p 358-9 Intro to Spectroscopy, 3rd ed., Pavia et al.

UV-Vis Spectroscopy: CONJUGATION

http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/UV-Vis/spectrum.htm

p 363 Intro to Spectroscopy, 3rd ed., Pavia et al.

UV-Vis Spectroscopy: Aromatic Compounds

p 375-76 Intro to Spectroscopy, 3rd ed., Pavia et al.

UV-Vis: Aromatics

p 379 Intro to Spectroscopy, 3rd ed., Pavia et al.

UV-Vis: Acid/Base

p 377 Intro to Spectroscopy, 3rd ed., Pavia et al.

UV-Vis: Acid/Base

Nature of ShiftDescriptive Term

To Longer Wavelength Bathochromic

To Shorter Wavelength Hypsochromic

To Greater Absorbance Hyperchromic

To Lower Absorbance Hypochromic

Terminology for Absorption Shifts

UV-Vis: Acid/Base

 

UV-Vis: Empirical Rules

p 380 Intro to Spectroscopy, 3rd ed., Pavia et al.

 

UV-Vis: Empirical Rules

p 380 Intro to Spectroscopy, 3rd ed., Pavia et al.