15. Analytical Techniques:IR, NMR, Mass Spect

Predict the masses and the structures of the most abundant fragments observed in the mass spectra of the following compounds.

(c) 4-methylpentan-2-ol

Predict the masses and the structures of the most abundant fragments observed in the mass spectra of the following compounds.

(b) 3-methylhex-2-ene

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

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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Ethers are not easily differentiated by their infrared spectra, but they tend to form predictable fragments in the mass spectrum. The following compounds give similar but distinctive mass spectra.

Both compounds give prominent peaks at m/z 116, 73, 57, and 43. But one compound gives a distinctive strong peak at 87, and the other compound gives a strong peak at 101. Determine which compound gives the peak at 87 and which one gives the peak at 101. Propose fragmentations to account for the ions at m/z 116, 101, 87, and 73.

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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A laboratory student added 1-bromobutane to a flask containing dry ether and magnesium turnings. An exothermic reaction resulted, and the ether boiled vigorously for several minutes. Then she added acetone to the reaction mixture and the ether boiled even more vigorously. She added dilute acid to the mixture and separated the layers. She evaporated the ether layer, and distilled a liquid that boiled at 143 °C. GC–MS analysis of the distillate showed one major product with a few minor impurities. The mass spectrum of the major product is shown here.

(b) Explain why the molecular ion is or is not visible in the mass spectrum, and show what ions are likely to be responsible for the strong peaks at m/z 59 and 101.

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

b.

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

f.

Primary alcohols have a strong peak at m/z = 31.

a. What fragment is responsible for this peak?

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

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

c.

The mass spectra of 1-methoxybutane, 2-methoxybutane, and 2-methoxy-2-methylpropane are shown below. Match each compound with its spectrum.

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