Ch 9 Answers - Chem 345 SFN 1.a Write the number of signals...

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Solutions to NMR Questions Chem. 345 SFN 1.a. Write the number of signals in the proton-decoupled 13 C NMR spectrum for each isomer: MeO OMe OMe OMe MeO OMe MeO OMe A B C D 3 5 3 4 For isomers with the same number of signals, how could you tell them apart by 13 C NMR? Off-resonance or DEPT spectra would show CH 3 CH 2 and CH 2 for A but CH 3 , CH 3 , and C q for C There would also be significant chemical shift differences, but we do not cover 13 C NMR chemical shift predictions in enough detail here to allow you to predict 13 C NMR spectra well. b. Write in the hydrogens on the structure, assign different hydrogens letters from left to right, and sketch the 1 H NMR spectrum, showing multiplicities, number of H causing the signal, and your letter assignments for each group of peaks. 1.b.1 0 δ 5 10 H 3 C O C H 2 H 2 C CH 3 O A B C D 3 3 2 2 A D C B 1.b.2 0 δ 5 10 C H 2 CH 3 C O H H H CH 3 H A B C D 5 A (singlet to non- first order pattern) 2 B 1 6 D C
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2 2. Interpreting 1 H-NMR spectra. When asked for a part-structure, you must circle the H’s being observed to get full credit. 2.a. C 4 H 7 ClO 2 . The “3” and “4 are integrations of the regions shown __1__ DBE A Part-structure from “3” region C B O-CH 2 -CH 3 Part structures from “4” region [note: signals for two types of H partially overlap] X-CH 2 - -CH 2 -CH 3 singlet quartet Complete structure (label the proper H’s with letters, and insert them on the spectrum) 2.b. The signal at the right integrates for one H. 2.b.1. From the chemical shift, give a part-structure that is consistent H-C-X (hydrogen on carbon bearing heteroatom) 2.b.2 Show two part-structures that are consistent with the multiplicity. You cannot tell exactly what substituents are attached, but should be able to suggest ones that are consistent with the chemical shift. Circle the observed hydrogen C H C H X H 2 C X = O or halogen in both structures The lines might connect to anything but hydrogen C C H X CH 3 Cl-CH 2 -C-O-CH 2 -CH 3 O A B C
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3 3. Interpreting 1 H-NMR spectra. When asked for a part-structure, you must circle the H’s being observed to get full credit.
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