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Chapter 9: Problem 25

Write the structure of the major organic product isolated from the reaction of 3 -hexyne with (a) Hydrogen ( 2 mol), platinum (f) Chlorine \((2 \mathrm{~mol})\) (b) Hydrogen ( 1 mol), Lindlar palladium (g) Aqueous sulfuric acid, mercury(II) sulfate (c) Hydrogen chloride ( \(1 \mathrm{~mol}\) ) (h) Ozone followed by hydrolysis (d) Hydrogen chloride ( \(2 \mathrm{~mol}\) ) (e) Chlorine (1 mol)

Short Answer

Expert verified
Major products: (a) hexane, (b) cis-3-hexene, (c) 3-chloro-3-hexene, (d) 3,3-dichlorohexane, (e) trans-3,4-dichlorohexene, (f) 3,3,4,4-tetrachlorohexane, (g) 3-hexanone, (h) propanoic acid and butanoic acid.

Step by step solution

01

Hydrogenation with 2 mol H2 and Platinum

When 3-hexyne is treated with 2 moles of hydrogen (H2) in the presence of platinum, it undergoes full hydrogenation, converting the alkyne into an alkane. The triple bond in 3-hexyne is reduced to a single bond, resulting in hexane.
02

Hydrogenation with 1 mol H2 and Lindlar Palladium

Using 1 mol of hydrogen (H2) and Lindlar's catalyst, an alkyne can be selectively hydrogenated to a cis-alkene. Thus, 3-hexyne is converted to cis-3-hexene.
03

Reaction with 1 mol of Hydrogen Chloride

Adding 1 mol of HCl to 3-hexyne results in the addition of H and Cl across the triple bond, forming 3-chloro-3-hexene. This follows Markovnikov's rule, where Cl attaches to the more substituted carbon.
04

Reaction with 2 mol of Hydrogen Chloride

With 2 mol of HCl, 3-hexyne undergoes a full addition reaction to give 3,3-dichlorohexane. Both chlorines add to the same carbon following Markovnikov's rule.
05

Reaction with 1 mol of Chlorine

1 mol of Cl2 adds across the triple bond in 3-hexyne to form trans-3,4-dichlorohexene through an anti-addition mechanism, resulting in trans stereochemistry.
06

Reaction with 2 mol of Chlorine

Adding 2 mol of Cl2 to 3-hexyne results in a tetrachloride product, specifically 3,3,4,4-tetrachlorohexane, as the alkyne is converted to a saturated compound.
07

Hydration with Aqueous Sulfuric Acid and Mercury(II) Sulfate

This reaction yields a keto product through mercuric ion-catalyzed hydration of the alkyne, resulting in 3-hexanone, following Markovnikov addition.
08

Ozonolysis Followed by Hydrolysis

Ozonolysis of 3-hexyne followed by hydrolysis breaks the triple bond and forms two carboxylic acids, propanoic acid and butanoic acid.

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Key Concepts

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

Hydrogenation
Hydrogenation is a fundamental reaction in organic chemistry where hydrogen is added to unsaturated bonds, like double or triple bonds, converting them into single bonds. This transformation often uses catalysts such as platinum or palladium to increase the reaction speed and efficiency.
  • In full hydrogenation, 3-hexyne reacts with 2 moles of hydrogen in the presence of a platinum catalyst. This turns the alkyne's triple bond into a single bond, forming an alkane, specifically hexane.
  • Lindlar's catalyst can be employed for partial hydrogenation. It allows 3-hexyne to perform a selective reaction with 1 mole of hydrogen, producing cis-3-hexene, a type of alkene.
Understanding hydrogenation helps in controlling the type of product formed, whether it retains double bonds or becomes fully saturated.
Markovnikov's Rule
Markovnikov's Rule is crucial when adding acids like HCl to compounds with multiple bonds, as it predicts where the atoms will attach. Essentially, it states that during a reaction, the hydrogen will be added to the carbon with more hydrogen atoms, whereas the other atom, like chlorine, will attach to the more substituted carbon.
  • Applying the rule to 3-hexyne, when 1 mol of HCl is added, hydrogen bonds with the less substituted carbon while chlorine attaches to the more substituted carbon, forming 3-chloro-3-hexene.
  • With 2 mol of HCl, both chlorines follow the same pattern of addition, resulting in 3,3-dichlorohexane.
Markovnikov's Rule is a guideline to predict the outcome of addition reactions in unsaturated hydrocarbons.
Alkyne Reactions
Alkynes are hydrocarbons with at least one carbon-carbon triple bond. They undergo various reactions, driven by the high energy of the triple bond.
  • When 3-hexyne reacts with chlorine, different products can form depending on the amount of chlorine. With 1 mol, a process called anti-addition results, producing trans-3,4-dichlorohexene due to the mechanism of the reaction.
  • When 2 mol of chlorine is used, the reaction proceeds to form a tetrachloride, 3,3,4,4-tetrachlorohexane, effectively converting the alkyne to a saturated hydrocarbon.
Understanding different alkyne reactions helps in synthesizing various complex molecules from basic hydrocarbon structures.
Ozonolysis
Ozonolysis is a reaction where ozone ( O_3 ) slices through unsaturated bonds, leading to the breakdown of hydrocarbons. When followed by hydrolysis, this process converts triple bonds into two distinct groups.
  • For 3-hexyne, ozonolysis followed by hydrolysis results in the cleavage of the triple bond and the formation of two carboxylic acids, specifically propanoic acid and butanoic acid.
This reaction is useful for methodically examining the structure of unsaturated hydrocarbons by breaking them down into these smaller fragments.
Mercury(II) Sulfate Catalysis
Mercury(II) sulfate catalysis provides a means to hydrate alkynes, converting them into ketones. Through this catalytic process, alkynes engage in Markovnikov addition.
  • When 3-hexyne is treated with aqueous sulfuric acid and mercury(II) sulfate, it undergoes a reaction to form a keto product, in this case, 3-hexanone.
These reactions demonstrate how alkynes can be functionalized beyond simple carbon chain manipulations, turning unsaturated molecules into valuable compounds with specific functional groups.

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Most popular questions from this chapter

\((Z)-9-\) Tricosene \(\left[(Z)-\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{7} \mathrm{CH}=\mathrm{CH}\left(\mathrm{CH}_{2}\right)_{12} \mathrm{CH}_{3}\right]\) is the sex pheromone of the female housefly. Synthetic \((Z)-9\) -tricosene is used as bait to lure male flies to traps that contain insecticide. Using acetylene and alcohols of your choice as starting materials, along with any necessary inorganic reagents, show how you could prepare (Z)-9-tricosene.

Outline efficient syntheses of each of the following alkynes from acetylene and any necessary organic or inorganic reagents: (a) 1-Heptyne (b) 2 -Heptyne (c) 3-Hentyne

A certain hydrocarbon had the molecular formula \(\mathrm{C}_{16} \mathrm{H}_{26}\) and contained two triple bonds. Ozonolysis gave \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{4} \mathrm{CO}_{2} \mathrm{H}\) and \(\mathrm{HO}_{2} \mathrm{CCH}_{2} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}\) as the only products. Suggest a reasonable structure for this hydrocarbon.

Nucleophilic addition can occur with alkynes that bear strong electron- attracting substituents such as \(\mathrm{CF}_{3}\) on the triple bond. Predict the product of nucleophilic addition of \(\mathrm{CH}_{3} \mathrm{OD}\) to \(3,3,3\) -trifluoropropyne. The stereochemistry of addition is anti, and the first step in the mechanism is bond formation between \(\mathrm{CH}_{3} \mathrm{O}^{-}\) and one of the carbons of the triple bond.

Show by writing a suitable series of equations how you could prepare each of the following compounds from the designated starting materials and any necessary organic or inorganic reagents: (a) 2,2 -Dibromopropane from \(1,1-\) dibromopropane (b) 2,2 -Dibromopropane from 1,2 -dibromopropane (c) \(1,1,2,2\) -Tetrachloropropane from 1,2 -dichloropropane (d) 2,2-Diiodobutane from acetylene and ethyl bromide (e) 1-Hexene from 1-butene and acetylene (f) Decane from 1-butene and acetylene (g) Cyclopentadecyne from cyclopentadecene
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