Textbook Question
Hydration of alkynes (via oxymercuration) gives good yields of single compounds only with symmetrical or terminal alkynes. Show what the products would be from hydration of each compound.
c. hex-1-yne
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Ch. 18 - Ketones and Aldehydes
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 18, Problem 64a
Hydration of alkynes (via oxymercuration) gives good yields of single compounds only with symmetrical or terminal alkynes. Show what the products would be from hydration of each compound.
a. hex-3-yne
Verified step by step guidance1
Step 1: Understand the reaction mechanism. Hydration of alkynes via oxymercuration involves the addition of water (H₂O) across the triple bond in the presence of a catalyst, typically mercuric sulfate (HgSO₄) and sulfuric acid (H₂SO₄). This reaction proceeds through a Markovnikov addition, where the hydroxyl group (-OH) attaches to the more substituted carbon.
Step 2: Analyze the structure of hex-3-yne. Hex-3-yne is an internal alkyne with the triple bond located between the third and fourth carbons in a six-carbon chain. Since it is not terminal or symmetrical, the hydration will produce a mixture of products due to the lack of regioselectivity.
Step 3: Predict the intermediate. The reaction proceeds through the formation of an enol intermediate (a compound with a hydroxyl group attached to a carbon-carbon double bond). The enol is unstable and undergoes tautomerization to form a ketone.
Step 4: Identify the possible ketones. The enol formed from hex-3-yne hydration can tautomerize to produce two ketones: one with the carbonyl group on the third carbon (3-hexanone) and the other with the carbonyl group on the fourth carbon (4-hexanone).
Step 5: Summarize the outcome. Since hex-3-yne is an internal alkyne, the hydration reaction will yield a mixture of 3-hexanone and 4-hexanone as the final products due to the lack of regioselectivity in the addition of water.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Alkynes
Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond. They are unsaturated compounds and can undergo various reactions, including hydration. The position of the triple bond in the alkyne affects the product formed during reactions, particularly in terms of regioselectivity and stereochemistry.
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Alkyne Hydration
Oxymercuration-Demercuration
Oxymercuration-demercuration is a two-step reaction used to hydrate alkenes and alkynes. In the first step, mercuric acetate reacts with the alkyne to form a mercurial intermediate, which is then treated with water to yield an alcohol. This method is particularly useful for achieving Markovnikov selectivity, where the more substituted carbon receives the hydroxyl group.
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05:General properties of oxymercuration-reduction.
Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In the context of alkyne hydration, the position of the triple bond influences which carbon atom will bond with the hydroxyl group, leading to different products based on whether the alkyne is symmetrical or terminal.
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Related Practice
Textbook Question
Hydration of alkynes (via oxymercuration) gives good yields of single compounds only with symmetrical or terminal alkynes. Show what the products would be from hydration of each compound.
d. cyclodecyne
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Textbook Question
Two structures for the sugar glucose are shown on page 914. Interconversion of the open-chain and cyclic hemiacetal forms is catalyzed by either acid or base.
(b) The cyclic hemiacetal is more stable than the open-chain form, so very little of the open-chain form is present at equilibrium. Will an aqueous solution of glucose reduce Tollens reagent and give a positive Tollens test? Explain.
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Textbook Question
Hydration of alkynes (via oxymercuration) gives good yields of single compounds only with symmetrical or terminal alkynes. Show what the products would be from hydration of each compound.
b. hex-2-yne
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Textbook Question
Two structures of the sugar fructose are shown next. The cyclic structure predominates in aqueous solution.
(a) Number the carbon atoms in the cyclic structure. What is the functional group at C2 in the cyclic form?
(b) Propose a mechanism for the cyclization, assuming a trace of acid is present.
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Textbook Question
Two structures for the sugar glucose are shown on page 914. Interconversion of the open-chain and cyclic hemiacetal forms is catalyzed by either acid or base.
(a) Propose a mechanism for the cyclization, assuming a trace of acid is present.