NMR Quiz in organic chemistry

Topics: NMR spectroscopy, Nuclear magnetic resonance, Proton NMR Pages: 2 (474 words) Published: September 24, 2013
8. Terfenedine is an amino diol that is the active ingredient in the antihistamine Seldane. Mass spectral analysis of terfenedine shows a molecular ion at m/z = 471 and a peak at m/z = 472 which is 35.5% the height of the molecular ion. Terfenedine is known to contain C, H, O and N. (a) Suggest five molecular formulas for terfenedine.

(b) Terfenedine has an even number of carbons and contains nine double bonds and four rings. Based on this additional information, what is the formula for terfenedine? (c) Explain the origin of the peak at m/z = 472. (12 pts.)

9. Explain why all protons in a molecule do not absorb rf (radio frequency) energy at the same frequency. (5 pts.)

10. Answer the following questions. (10 pts.) (a) How many groups of peaks do you expect for the 1H NMR spectrum of styrene oxide?
stryene oxide
(b) Draw a tree diagram for the proton-2 (H2) signal. The relative coupling constants should be expressed in your diagram.

11. Propose a structure for compound A, which has M+ = 86 in its mass spectrum, an IR absorption at 3400 cm−1, and the following 13C NMR spectral data: (6 pts.) Compound A

Broadband-decoupled 13C NMR: δ 30.2, 31.9, 61.8, 114.7, 138.4
DEPT-90: δ 138.4
DEPT-135: positive peak at δ 138.4; negative peaks at δ 30.2, 31.9, 61.8, 114.7

12. Refer to the mass spectrum of a hydrocarbon shown below to answer the following questions. (12 pts.)
(a) What peak represents the molecular ion (M+)?
(b) What peak represents the base peak?
(c) Propose plausible molecular structures for the hydrocarbon. (d) Propose structures for the fragment ions at m/z = 57, 43, and 29 based on your answer (c).

13. Match a structure from the list below to the following IR spectra. Place the letter of the structure in the blank to the left of the...
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