15. Analytical Techniques:IR, NMR, Mass Spect

2-Methylnonan-4-one can undergo two different McLafferty rearrangements. Draw the products of each of them.

The following spectra for A and B correspond to two structural isomers. The NMR singlet at δ1.16 in spectrum A disappears when the sample is shaken with D₂O. The singlet at δ0.6 ppm in the spectrum of B disappears on shaking with D₂O. Propose structures for these isomers, and show how your structures correspond to the spectra. Show what cleavage is responsible for the base peak at m/z 44 in the mass spectrum of A and the prominent peak at m/z 58 in the mass spectrum of B.

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Draw the most likely ion fragment of the molecule

Using curved arrows, show the principal fragments you would expect to see in the mass spectrum of each of the following compounds:

b.

Account for the peaks at m/z 87, 111, and 126 in the mass spectrum of 2,6-dimethylheptan-4-ol.

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An unknown compound gives a mass spectrum with a weak molecular ion at m/z 113 and a prominent ion at m/z 68. Its NMR and IR spectra are shown here. Determine the structure, and show how it is consistent with the observed absorptions. Propose a favorable fragmentation to explain the prominent MS peak at m/z 68.

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The mass spectrum of tert-butylamine follows shows an intense base peak at m/z 58, and very little else. Use a diagram to show the cleavage that accounts for the base peak. Suggest why no molecular ion is visible in this spectrum.

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.

b. Show the mechanism for formation of the peak at m/z = 84.

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

(b)

Using curved arrows, show the principal fragments you would expect to see in the mass spectrum of each of the following compounds:

c.

A student added 3-phenylpropanoic acid (PhCH₂CH₂COOH) to a molten salt consisting of a 1:1 mixture of NaCl and AlCl₃ maintained at 170 °C. After 5 minutes, he poured the molten mixture into water and extracted it into dichloromethane. Evaporation of the dichloromethane gave a 96% yield of the product whose spectra follow. The mass spectrum of the product shows a molecular ion at m/z 132. What is the product?

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A mass spectrum shows significant peaks at m/z = 87, 115, 140, and 143. Which of the following compounds is responsible for that mass spectrum?

The following compounds undergo McLafferty rearrangement in the mass spectrometer. Predict the masses of the resulting charged fragments.

(b) 3-methylhexan-2-one

Using curved arrows, show the principal fragments you would expect to see in the mass spectrum of each of the following compounds:

f.