15. Analytical Techniques:IR, NMR, Mass Spect

Four infrared spectra are shown, corresponding to four of the following compounds. For each spectrum, determine the structure and explain how the peaks in the spectrum correspond to the structure you have chosen.

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Predict the characteristic infrared absorptions of the functional groups in the following molecules.

(d) pent-1-yne

(e) diethylamine

(f) pentanoic acid

Predict the characteristic infrared absorptions of the functional groups in the following molecules.

(a) cyclohexene

(b) pentan-2-ol

(c) pentan-2-one

These five structures all have distinguishing absorptions in the IR. Match each structure with its characteristic absorption.

(a) sharp, 2254 cm^–1

(b) very broad, centered about 3330 cm^–1

(c) strong, slightly broadened, 1645 cm^–1

(d) broad with spikes at 3367 and 3292 cm^–1

(e) strong, sharp 1717 cm^–1

Three common lab experiments are shown. In each case, describe how the IR spectrum of the product would differ from that of the reactant. Give approximate frequencies for distinctive peaks in the IR spectrum of the reactant and also that of the product.

Give approximate wavenumbers for the major characteristic IR absorption bands that would be given by each of the following compounds:

e.

f.

For each of the following pairs of compounds, name one absorption band that can be used to distinguish between them.

e.

f.

Norlutin and Enovid are ketones that suppress ovulation, so they have been used clinically as contraceptives. For which of these compounds would you expect the infrared carbonyl absorption (C=O stretch) to be at a higher frequency? Explain.

Give approximate wavenumbers for the major characteristic IR absorption bands that would be given by each of the following compounds:

a.

b.

Rank the following compounds from highest wavenumber to lowest wavenumber for their C-O absorption band:

Rank the following compounds from highest wavenumber to lowest wavenumber for their C=O absorption band:

How can IR spectroscopy distinguish between 1-hexyne, 2-hexyne, and 3-hexyne?

a. How could you use IR spectroscopy to determine whether the following reaction had occurred?

b. After purifying the product, how could you determine whether all the NH₂NH₂ had been removed?

For each of the following pairs of compounds, identify one IR absorption band that could be used to distinguish between them:

i.

j.

For each of the following pairs of compounds, identify one IR absorption band that could be used to distinguish between them:

c. CH₃CH₂CH₂OH and CH₃CH₂OCH₃

d.