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UV-Vis Spectroscopy

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Presentation on theme: "UV-Vis Spectroscopy"— Presentation transcript:

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

2 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 Spectroscopy HPLC: Peak Area vs Detector setting Excedrin ES 250 mg aspirin; 250 mg acetaminophen; 65 mg caffeine

3 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

4 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

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

6 Chromo- phore ExampleExcitationλ max, nmεSolvent C=CEtheneπ __ > π*17115,000hexane C≡C1-Hexyneπ __ > π*18010,000hexane C=OEthanal n __ > π* π __ > π* 290 180 15 10,000hexane N=O Nitro- methane n __ > π* π __ > π* 275 200 17 5,000ethanol C-X X=Br X=I Methyl bromide Methyl Iodide n __ > σ* 205 255 200 360hexane UV-Vis: Chromophores http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/UV-Vis/spectrum.htm

7 UV-Vis Spectroscopy: Chromophores Table 7.3, p 362 Intro to Spectroscopy, 3 rd ed., Pavia et al.

8 UV-Vis Spectroscopy: Solvents p 358-9 Intro to Spectroscopy, 3 rd ed., Pavia et al.

9 UV-Vis Spectroscopy: CONJUGATION http://www.cem.msu.edu/~reusch/VirtualText/ Spectrpy/Spectrpy/UV-Vis/spectrum.htm p 363 Intro to Spectroscopy, 3 rd ed., Pavia et al.

10 UV-Vis Spectroscopy: Aromatic Compounds p 375-76 Intro to Spectroscopy, 3 rd ed., Pavia et al.

11 UV-Vis: Aromatics p 379 Intro to Spectroscopy, 3 rd ed., Pavia et al.

12 UV-Vis: Acid/Base p 377 Intro to Spectroscopy, 3 rd ed., Pavia et al.

13 UV-Vis: Acid/Base Nature of Shift Descriptive Term To Longer WavelengthBathochromic To Shorter WavelengthHypsochromic To Greater AbsorbanceHyperchromic To Lower AbsorbanceHypochromic Terminology for Absorption Shifts

14 UV-Vis: Acid/Base

15 UV-Vis: Empirical Rules p 380 Intro to Spectroscopy, 3 rd ed., Pavia et al.

16 UV-Vis: Empirical Rules p 380 Intro to Spectroscopy, 3 rd ed., Pavia et al.


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