Domanda del libro di testo
Draw the structures of the compound methyl α-D-galactopyranoside.
Allose is the C3 epimer of glucose, and ribose is the C2 epimer of arabinose.
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Ch. 23 - Carbohydrates and Nucleic Acids
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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TOC.tableOfContents
- 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
Capitolo 23, Problema 22
The mechanism of glycoside formation is the same as the second part of the mechanism for acetal formation. Propose a mechanism for the formation of methyl β-D-glucopyranoside.
Guida verificata passo dopo passo1
Start by identifying the reactants: D-glucose (a monosaccharide) and methanol (CH₃OH). The reaction typically occurs in the presence of an acid catalyst, such as HCl or H₂SO₄, to facilitate the process.
Protonate the anomeric hydroxyl group (-OH) of D-glucose using the acid catalyst. This step increases the electrophilicity of the anomeric carbon, making it more susceptible to nucleophilic attack.
After protonation, the anomeric hydroxyl group leaves as water (H₂O), forming a resonance-stabilized oxocarbenium ion intermediate. This intermediate is crucial for the reaction to proceed.
Methanol (CH₃OH) acts as a nucleophile and attacks the positively charged anomeric carbon of the oxocarbenium ion. This step forms a new bond between the anomeric carbon and the oxygen of methanol.
Finally, deprotonate the methanol group attached to the anomeric carbon to neutralize the charge and form methyl β-D-glucopyranoside. The β-configuration is determined by the stereochemistry of the nucleophilic attack on the oxocarbenium ion.
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Concetti chiave
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Glycoside Formation
Glycoside formation involves the reaction between a sugar and an alcohol, resulting in the creation of a glycosidic bond. This process typically requires an acid catalyst to protonate the hydroxyl group of the sugar, making it a better leaving group. The alcohol then attacks the anomeric carbon, leading to the formation of the glycoside. Understanding this mechanism is crucial for proposing the formation of methyl β-D-glucopyranoside.
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Predict the structure of the glycoside products
Acetal Formation
Acetal formation is a reaction where an aldehyde or ketone reacts with an alcohol in the presence of an acid catalyst to form an acetal. This process involves the nucleophilic attack of the alcohol on the carbonyl carbon, followed by the loss of water and the formation of a stable acetal. The similarity between glycoside and acetal formation lies in the mechanism, where both involve nucleophilic attack and the formation of a new bond, which is essential for understanding the proposed mechanism.
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04:29Acetal Protecting Group
Mechanism of Nucleophilic Substitution
The mechanism of nucleophilic substitution is fundamental in organic chemistry, where a nucleophile replaces a leaving group in a molecule. In the context of glycoside formation, the alcohol acts as the nucleophile, attacking the electrophilic carbon of the sugar. This process can occur via either an SN1 or SN2 mechanism, depending on the structure of the substrate and the conditions. Recognizing this mechanism is vital for accurately proposing the steps involved in synthesizing methyl β-D-glucopyranoside.
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01:47Nucleophiles and Electrophiles can react in Substitution Reactions.
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