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8 - Electronic Spectroscopy, Mass Spectrometry

8 - Electronic Spectroscopy, Mass Spectrometry - Today NMR...

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Today: NMR Mass Spectrometry Electronic Spectroscopy (quasi-review of vib & rot) Chemistry in Context
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1 1 1 1 2 1 1 3 3 1 Why Pascal s triangle? -CH 3 Take the case of a splitting by 3 equivalent H-atoms
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o o How about this molecule? First, identify all of the protons
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o o Now, identify which protons are unique o o H H H H H H H H H H H H H H
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o o o o a (3) b (2) c (2) d (2) (2) e (2) f (1) g f e Next, identify splittings using Pascal s triangle o o H H H H H H H H H H H H H H These protons are not going to be split
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o o a (3) b (2) c (2) d (2) (2) e (2) f (1) g f e Split by 2 protons Split by 5 protons Split by 2 protons 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 6 15 20 15 6 1 Split by 0 protons unsplit Next, what are relative integrated peak intensities?
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o o a (3) b (2) c (2) d (2) (2) e (2) f (1) g f e Split by 2 protons Split by 5 protons Split by 2 protons 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 6 15 20 15 6 1 Split by 0 protons unsplit Intensity = 5 2 2 2 3 Next, what are relative chemical shifts of these peaks?
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o o a (3) b (2) c (2) d (2) (2) e (2) f (1) g f e a, b c d e-f
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o o a (3) b (2) c (2) d (2) (2) e (2) f (1) g f e Split by 2 protons Split by 5 protons Split by 2 protons 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 6 15 20 15 6 1 Split by 0 protons unsplit Intensity = 5 2 2 2 3 Most highly shielded (largest + chemical shift) Least shielded (smallest + chemical shift) Order might be shifted So identify by intensity
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o Answer
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C 3 H 6 O 2 Numbers represent relative peak areas of multiplets 1 H NMR spectra: which molecule? H 3 C C O OCH 3 04-8 H 3 C-CH 2 -COH formula O =
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C 3 H 6 O 2 Numbers represent relative peak areas of multiplets 1 H NMR spectra of methyl acetate H 3 C C O OCH 3 04-8
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formula C 5 H 10 O 1 H NMR spectra of which molecule? CH 3 CH 2 C O CH 2 CH 3 04-9 H 3 C-(CH 2 ) 3 -CH 2 OH
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C 5 H 10 O 1 H NMR spectra of diethylketone CH 3 CH 2 C O CH 2 CH 3 04-9
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C 4 H 8 O 2 1 H NMR spectra of ? 04-10 What is the correct structure?
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C 5 H 10 O 1 H NMR spectra of diethylketone CH 3 CH 2 C O CH 2 CH 3 04-9
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Molecular Electronic Spectroscopy: Tying together MO theory, vibrational spectroscopy, and rotational spectroscopy CHALK TIME
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Molecular Electronic Spectroscopy E time Q ±² (Longer bond = bigger dipole) HC Ł N: p- V p- S p- p- p- V p- S p- p- HC = N: HC Ł N: p- V p- S p- p-
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Molecular Electronic Spectroscopy Energy v=0 v=1 v=2 v=3 rotational states (J = 0,1,2…)
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