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Chapter 12: Problem 63

Give the structure of an alkene that will give the following carbonyl compounds upon ozonolysis followed by reduction with \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{~S}\). (a) \(\mathrm{CH}_{3} \mathrm{CHO}\) only (b) \(\mathrm{CH}_{3} \mathrm{CHO}\) and \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHO}\) (c) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{O}\) and \(\mathrm{H}_{2} \mathrm{C}=\mathrm{O}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CCH}_{3}\) and \(\mathrm{CH}_{3} \mathrm{CHO}\) (e) Cyclopentanone and \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHO}\)

Short Answer

Expert verified
(a): \(\mathrm{CH_2=CH_2}\) (b): \(\mathrm{CH_2=CH-CH_2-CH_3}\) (c): \(\mathrm{CH_2=C(CH_3)_2}\) (d): \(\text{trans-1,2-dimethylcyclohex-3-ene} \(e): \(\text{1,2,3,4-tetrahydronaphthalene-}1,4,3-(CH_2)_2

Step by step solution

01

Understand the Ozonolysis Reaction

Ozonolysis is a reaction where an alkene reacts with ozone \((O_3)\), leading to the cleavage of the double bonds to form carbonyl compounds (aldehydes or ketones) after reduction.
02

Analyze the Provided Compounds

Consider the given compounds to deduce the structure of the initial alkene. Ozonolysis splits the alkene at the double bond, each part forming a carbonyl compound.
03

Case (a) Methanal

For \(\mathrm{CH_3CHO}\) only: The initial alkene should be \(\mathrm{CH_2=CH_2}\). Ozonolysis of ethene (ethene) will yield only formaldehyde.
04

Case (b) Ethanal and Propanal

For both \(\mathrm{CH_3CHO}\) and \(\mathrm{CH_3CH_2CHO}\): The initial alkene should be \(\mathrm{CH_2=CH-CH_2-CH_3}\). Ozonolysis of but-2-ene will yield formaldehyde and acetaldehyde.
05

Case (c) Acetone and Formaldehyde

For \(\left(\mathrm{CH_3}\right)_2C=O\) and \(\mathrm{CH_2O}\): The initial alkene should be \(\left(\mathrm{CH_2=C(CH_3)_2}\right)\). Ozonolysis of 2-methylpropene will yield acetone and formaldehyde.
06

Case (d) 3-Pentanone and Acetaldehyde

For \(\mathrm{CH_3CH_2CCH_3}\) and \(\mathrm{CH_3CHO}\): The initial alkene should be \(\left(\text{trans-1,2-dimethylcyclohex-3-ene}\right)\). Ozonolysis of this compound will yield 3-pentanone and acetaldehyde.
07

Case (e) Cyclopentanone and Propanal

For \(\mathrm{Cyclopentanone}\) and \(\mathrm{CH_3CH_2CHO}\): The initial alkene should be \(\left(\text{1,2,3,4-tetrahydronaphthalene-}1,4,3-(CH_2)_2\right)\). Ozonolysis of this compound will yield cyclopentanone and propanal.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

alkenes
Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C). These double bonds are sites of high reactivity, making alkenes important in many chemical reactions. In organic synthesis, alkenes serve as starting materials for a variety of reactions including ozonolysis. Alkenes can be converted into different functional groups, making them versatile intermediates in organic chemistry.
carbonyl compounds
Carbonyl compounds are organic molecules that contain a carbon-oxygen double bond (C=O). These compounds include aldehydes and ketones. In organic synthesis, carbonyl compounds are often formed from the cleavage of alkenes through ozonolysis. For example, ozonolysis of ethene yields formaldehyde (an aldehyde), while ozonolysis of 2-methylpropene produces acetone (a ketone) and formaldehyde.
reaction mechanisms
Understanding reaction mechanisms is crucial in organic chemistry. A reaction mechanism describes the step-by-step process by which reactants are transformed into products. In ozonolysis, the alkene first reacts with ozone to form an ozonide intermediate. This ozonide then breaks down in the presence of a reducing agent, such as \((\mathrm{CH}_{3}\mathrm{_{2}}\mathrm{S})\), to form carbonyl compounds. Knowing the mechanism helps in predicting the products of ozonolysis based on the structure of the starting alkene.
organic synthesis
Organic synthesis involves constructing complex organic molecules from simpler ones. Ozonolysis is a valuable tool in organic synthesis because it allows chemists to selectively break down alkenes to form carbonyl compounds. This can be useful in the synthesis of pharmaceuticals, agrochemicals, and other complex organic molecules. By choosing the right starting alkene and reaction conditions, specific carbonyl compounds can be obtained.
reduction reactions
Reduction reactions involve the gain of electrons or reduction of oxidation state by a molecule. In the context of ozonolysis, after the initial reaction with ozone, the resulting ozonide must be reduced to form stable carbonyl compounds. A common reducing agent used is \((\mathrm{CH}_{3}\mathrm{_{2}}\mathrm{S})\). This reduction step is crucial for breaking down the ozonide to yield the final product of aldehydes or ketones.

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Most popular questions from this chapter

Would you expect the catalytic hydrogenation of a small-ring cyclic alkene such as cyclobutene to be more or less exothermic than that of cyclohexene? (Hint: Which has more bond-angle strain, cyclobutene or cyclobutane?)

Diazomethane is the simplest member of the class of compounds called diazoalkanes or diazo compounds, \(\mathrm{R}_{2} \mathrm{C}=\mathrm{N}_{2}\). When diazo compound \(\mathrm{A}\) is irradiated in heptane solution at \(-78^{\circ} \mathrm{C}\), it gives a hydrocarbon, \(\mathrm{C}_{4} \mathrm{H}_{6}\), exhibiting three signals in 'H NMR and two signals in \({ }^{13} \mathrm{C}\) NMR spectroscopy, all in the aliphatic region. Suggest a structure for this molecule. $$ \mathrm{CH}_{2}=\mathrm{CHCH}_{2} \mathrm{CH}=\mathrm{N}=\mathrm{N}^{+} $$ \(\mathbf{A}\)

Treatment of 2 -methylpropene with catalytic deuterated sulfuric acid \(\left(\mathrm{D}_{2} \mathrm{SO}_{4}\right)\) in \(\mathrm{D}_{2} \mathrm{O}\) gives \(\left(\mathrm{CD}_{3}\right)_{3} \mathrm{COD}\). Explain by a mechanism.

Catalytic hydrogenation of \((S)-2,3\) -dimethyl-1-pentene gives only one optically active product. Show the product and explain the result. [Hint: Does addition of \(\mathrm{H}_{2}\) either (1) create a new stereocenter or (2) affect any of the bonds around the stereocenter already present?]

During the catalytic hydrogenation of the cis double bond in oleic acid, a naturally occurring fatty acid, the formation of some of the trans isomer is observed. Explain. Examine the mechanism Look for a pathway that could (1) allow rotation about the bond between the originally doublebonded carbons followed by (2) regeneration of a double bond with a trans configuration. \- The mechanism possesses two key features that are applicable to this problem. First, cach of the first three steps is reversible. Second, the two hydrogen atoms add to the carbons of the original double bond one at a time. Let us see how we can make use of these characteristics to define an isomerization pathway.
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