15. Analytical Techniques:IR, NMR, Mass Spect

The base peak in Figure 14.51 has m/z 45. Suggest a molecular formula and a structure for this fragment.

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Identify the compound that gives the mass spectrum and infrared spectrum shown here.

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The ultimate test of fluency in MS and IR is whether you can determine a moderately complex structure from just the MS and the IR, with no additional information. The IR and MS of a compound are shown below. Use everything you know about IR and MS, plus reasoning and intuition, to determine a likely structure. Then show how your proposed structure is consistent with these spectra.

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What hydrocarbons that contain a six-membered ring will have a molecular ion peak at m/z = 112?

Show the fragmentations that give rise to the peaks at m/z 43, 57, and 85 in the mass spectrum of 2,4-dimethylpentane (Figure 12-17).

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Suggest three ways that the following tertiary amine can fragment by α-cleavage. At which m/z would you expect to see peaks corresponding to these fragments?

For each of the molecules shown, predict the structure of at least one major fragment in the mass spectrum.

(e)

The mass spectrum for a compound with molecular weight of 102 is shown below. Its IR spectrum has a broad, strong absorption at 3600 cm^–1 and a medium absorption at 1360 cm^–1.

a. Identify the compound.

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What distinguishes the mass spectrum of 2,2-dimethylpropane from the mass spectra of pentane and isopentane?

An unknown compound gives the following mass, IR, and NMR spectra. Propose a structure, and show how it is consistent with the spectra. Show the fragmentations that give the prominent peaks at m/z 127 and 155 in the mass spectrum.

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In the mass spectrum of hexan-3-ol, identify the fragments arising from two α-cleavage fragmentations and one dehydration fragmentation.

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Propose a fragmentation to account for each numbered peak in the mass spectrum of n-butyl isopropyl ether.

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Why were no products from the McLafferty rearrangement observed in the spectrum of butan-2-one (Figure 18-3)?

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Predict the masses and the structures of the most abundant fragments observed in the mass spectra of the following compounds. (a) 2-methylpentane