Reviewquestions_13

Reviewquestions_13 - Organic Chemistry, 6e (Wade) Chapter...

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Organic Chemistry, 6e (Wade) Chapter 13: Nuclear Magnetic Resonance Spectroscopy 1 4) How many nuclear spin states are allowed for the 1 H nucleus? A) 1 B) 2 C) 3 D) 4 E) 10 Answer: B Diff: 1 7) Electromagnetic radiation in the __________ region is used in 1 H NMR spectroscopy. A) radio wave B) ultraviolet C) infrared D) microwave E) X-ray Answer: A Diff: 1 8) __________ is commonly used as an internal reference in NMR spectroscopy; its signal is assigned d = 0 in 1 H and 13 C NMR spectroscopy. Answer: Tetramethylsilane, (CH 3 ) 4 Si Diff: 2 11) The protons marked H a and H b in the molecule below are __________. A) chemically equivalent B) enantiotopic C) diastereotopic D) endotopic E) none of the above Answer: A Diff: 2 12) The protons marked H a and H b in the molecule below are __________. A) chemically equivalent B) enantiotopic C) diastereotopic D) endotopic E) none of the above Answer: C Diff: 3
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2 13) The protons marked H a and H b in the molecule below are __________. A) chemically equivalent B) enantiotopic C) diastereotopic D) endotopic E) none of the above Answer: B Diff: 3 15) How might the proton spectrum of ultrapure dimethylamine, (CH 3 ) 2 NH, differ from the spectrum of this compound to which D 2 O has been added? Answer: N-H signal will broaden or disappear upon addition of D 2 O as rapid hydrogen exchange occurs. Diff: 2 16) Give one reason why 13 C NMR is less sensitive than 1 H NMR. Answer: Natural isotopic abundance of 13 C is about 100 times less than that of 1 H or gyromagnetic ratio of 13 C is much smaller. Diff: 2 18) How might the two trimethylcyclohexane isomers shown below be most readily distinguished using NMR? Answer: Number of signals in 13 C NMR, 3 signals versus 6. Diff: 3
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19) What multiplicities are observed for the signals in the off-resonance decoupled 13 C spectrum of 2-chloropropene? A) 3 singlets B) 2 singlets and a doublet C) a singlet and 2 doublets D) a singlet, a doublet and a triplet E) a singlet, a triplet, and a quartet Answer: E Diff: 1 20) What multiplicities are observed in the off-resonance decoupled 13 C spectrum of 2,3-dimethyl-but-2-ene? Answer: a singlet and a quartet Diff: 2 21) Predict the number of signals expected (disregarding splitting) in the 1 H spectrum of m -xylene (1,3-dimethylbenzene). Answer: 4 Diff: 2 22) Predict the number of signals expected (disregarding splitting) in the 1 H spectrum of o -chlorophenol (2-chlorophenol). Answer: 5 Diff: 2 23) Predict the number of signals expected (disregarding splitting) in the 1 H spectrum of dibutyl ether. Answer: 4 Diff: 2 24) Predict the number of signals expected (disregarding splitting) in the 1 H spectrum of 1,1-dimethylcyclobutane. Answer: 3
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Reviewquestions_13 - Organic Chemistry, 6e (Wade) Chapter...

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