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Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
All textbooksBruice 8th EditionCh. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblem 60
Chapter 14, Problem 60

The IR spectrum of compound A with a molecular formula of C5H12O is shown below. Compound A is oxidized to give compound B, a ketone with a molecular formula of C5H10O. When compound A is heated with H2SO4, compounds C and D are obtained. Considerably more D is obtained than C. Reaction of compound C with O3, followed by treatment with dimethyl sulfide, gives two products: formaldehyde and compound E, with a molecular formula of C4H8O. Reaction of compound D with O3, followed by treatment with dimethyl sulfide, gives two products: compound F, with a molecular formula of C3H6O, and compound G, with a molecular formula of C2H4O. What are the structures of compounds A through G?
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Step 1: Analyze the molecular formula of compound A (C5H12O) and its IR spectrum. The presence of an -OH group can be inferred if there is a broad absorption around 3200-3600 cm⁻¹. This suggests that compound A is likely an alcohol.
Step 2: Consider the oxidation of compound A to compound B, which is a ketone (C5H10O). Oxidation of a secondary alcohol typically produces a ketone. This indicates that compound A is likely a secondary alcohol.
Step 3: Examine the dehydration reaction of compound A with H2SO4 to form compounds C and D. Dehydration of alcohols typically leads to alkenes. The fact that more of compound D is formed suggests that it is the more stable alkene, likely due to Zaitsev's rule (the more substituted alkene is favored).
Step 4: Analyze the ozonolysis of compound C. The products are formaldehyde (CH2O) and compound E (C4H8O). This indicates that compound C contains a terminal double bond, as ozonolysis cleaves double bonds to form carbonyl compounds.
Step 5: Analyze the ozonolysis of compound D. The products are compound F (C3H6O) and compound G (C2H4O). This suggests that compound D contains an internal double bond, as ozonolysis cleaves it to form two carbonyl compounds. Use the molecular formulas of the products to deduce the structure of compound D.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Infrared Spectroscopy (IR)

Infrared spectroscopy is a technique used to identify functional groups in organic compounds by measuring the absorption of infrared light. Different bonds absorb characteristic wavelengths of IR radiation, allowing chemists to deduce the presence of specific functional groups, such as alcohols, ketones, and alkenes, based on their unique absorption patterns.
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General Features of IR Spect

Oxidation and Reduction in Organic Chemistry

Oxidation in organic chemistry typically involves the loss of electrons or an increase in oxidation state, often resulting in the formation of carbonyl compounds like ketones or aldehydes. Understanding the oxidation states and the types of reactions that convert alcohols to ketones is crucial for predicting the transformations of compound A to compound B in the given question.
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Distinguishing between Oxidation and Reduction

Ozonolysis

Ozonolysis is a reaction involving the cleavage of alkenes using ozone (O3), which results in the formation of carbonyl compounds. This reaction is significant for determining the structures of compounds C, D, F, and G, as it helps identify the products formed from the oxidative cleavage of double bonds, leading to smaller carbonyl-containing fragments.
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General properties of ozonolysis.
Related Practice
Textbook Question

Which one of the following five compounds produced the IR spectrum shown below?

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Textbook Question

Five compounds are shown for each of the IR spectra below. Indicate which of the five compounds is responsible for each spectrum.

c.

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Textbook Question

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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Textbook Question

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

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Textbook Question

Each of the IR spectra shown below is accompanied by a set of four compounds. In each case, indicate which of the four compounds is responsible for the spectrum.

a.

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Textbook Question

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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