chm 2120 assignment 7

chm 2120 assignment 7 - H H H 3 C O H 7.7ppm 7.1 ppm i) O H...

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Assignment #7. 2009 NMR The following problems reflect closely the type of NMR questions you can expect on the final exam. They vary from very basic concept and interpretation of relatively simple spectra to more complex questions, the type that you might expect towards the end of the final exam. 1. Give the number of peaks expected for the indicated hydrogens in each of the following structures; H 3 C C H 2 C H 2 CH 3 O CH 3 H ? ? ? H 3 C H 2 C C H 2 H 2 C C H 2 H 2 C O CH 3 ? ? ? a) b) H H H 3 C O H ? c) The following require an understanding that the n+1 rule does not always hold since the coupling constants between the different Hs are not necessarily the same. Cl H H CH 3 O d) ? H H H CH 3 O ? e) ? 2) Explain why the chemical shift of aromatic hydrogens occurs at much lower field than those on staturated carbon. Draw a 'picture' to illustrate your answer. 3. Explain qualititively the indicated chemical shift differences. a) Basic level: CH 3 -O-CH 2 -O-CH 3 i) 3.5 ppm 5.3ppm ii) H 3 C CH 3 1.7 ppm 0.9 ppm Br 3.3 ppm 1.6ppm 1.3 ppm
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Unformatted text preview: H H H 3 C O H 7.7ppm 7.1 ppm i) O H H = 6.1ppm while H = 6.7ppm ii) N c) CH 3 H H = 5.6 = 4.2 ii) H 3 C O H 2 C C H 2 O O CH 3 3.6ppm 4.2ppm b) more advance level requiring understanding of how resonance affects electron density in a particular C-H bond Assign the structures to the following based on the molecular formula and the NMR spectrum given a) 1 2 3 4 5 6 PPM C 5 H 10 O 1 2 3 PPM C 5 H 10 O b) 2H 3H 2H 3H 1 2 3 4 5 6 7 8 PPM C 9 H 12 O c) 2 4 6 8 10 PPM 1H (s) 2H((d) 2H (d) 2H (q) 3H(t) d) C 9 H 12 O 2 1 2 3 4 5 PPM e) C 4 H 6 O 2 2H (t) 2H(t) 2H (quintet) 1 2 3 4 5 6 7 8 9 PPM e) C 10 H 12 O 5H [2:1:2] 2H 2H 3H For problems d) assign the four aromatic Hs to specific hydrogens in the molecule and e) assign the 5 aromatic Hs using your knowledge as to how substituents affect the chemical shifts of aromatic Hs....
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chm 2120 assignment 7 - H H H 3 C O H 7.7ppm 7.1 ppm i) O H...

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