PS 2 - NMR W12 Key corrected

PS 2 - NMR W12 Key corrected - Chem 112B W12 Problem Set 2...

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Chem 112B W12 Problem Set 2 Problem Set 2 – NMR Spectroscopy Answer Key Question 1. How many peaks would you see in the 1 H and 13 C spectra of the following molecules? Ignore any spin-spin coupling. Use your molecular models! a) 1 H: 3 (2 x CH 2 , OH) 13 C: 2 b) 1 H: 2 (symmetry) 13 C: 3 (Remember the C=O!) c) 1 H: 8 (CH 3 + all the other H) 13 C: 6 (all inequivalent) d) 1 H: 6 (2 x CH 3 , OH, CH and diastereotopic CH 2 ) 13 C: 5 e) 1 H: 9 (H a -H h + CH 3 ) see below 13 C: 6 Question 2. For the molecules below, I’ve highlighted some of the protons. Describe and DRAW the coupling pattern you would see in a 1 H NMR spectrum for each of the highlighted atoms. a) Red = triplet, blue = sextet, green = triplet
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Chem 112B W12 Problem Set 2 b) Red = doublet, blue = nonet (9 lines; coupling to 8 H – hard to draw!), green = doublet c) Both Singlets d) All Doublets of doublets – all 3 coupling constants are DIFFERENT e) Red = doublet, blue = doublet of doublets, green = doublet Question 3. Consider the spectrum below. It belongs to one of the four molecules A-D.
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Chem 112B W12 Problem Set 2 Quick point – there are a number of reasons why the incorrect answers are so. I’ve listed a few – you may have another. As long as it is a valid reason, you would get the marks on the exam . a) Is this the spectrum of molecule A? If not, state the clearest inconsistency with the structure of A. NO – too few protons, should see a 6H singlet for the OCH 3 groups rather than the 6H/4H triplet/quartet. b) Is this the spectrum of molecule B? If not, state the clearest inconsistency with the structure of B. YES c) Is this the spectrum of molecule C? If not, state the clearest inconsistency with the structure of C. No – the methyl groups are inequivalent, so you’d see two 3H triplets and one 2H quartet (also a quartet of doublets for the CH 2 next to the C=C) d) Is this the spectrum of molecule D? If not, state the clearest inconsistency with the structure of D. NO – you’ll get a 6H triplet, and a 4H quartet, but the molecule is symmetrical, so you’ll see a 2H singlet for the other protons.
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Chem 112B W12 Problem Set 2 e) Correlate the protons in the correct structure with the spectrum in terms of chemical shift, coupling pattern and integral. See spectrum (above) Question 4. Here are 5 molecules with the molecular formula C 5 H 12 O. For each part of this question, state which molecule is described by the spectral data. Give ONE reason that you chose your answer, based upon the spectral data. a) IR (cm
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This note was uploaded on 02/02/2012 for the course CHEM 112b taught by Professor Marsella during the Spring '11 term at UC Irvine.

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PS 2 - NMR W12 Key corrected - Chem 112B W12 Problem Set 2...

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