Domanda del libro di testo
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.
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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 24
Treatment of either anomer of fructose with excess ethanol in the presence of a trace of HCl gives a mixture of the α and β anomers of ethyl-D-fructofuranoside. Draw the starting materials, reagents, and products for this reaction. Circle the aglycone in each product.
Guida verificata passo dopo passo1
Draw the structure of D-fructose, which is a ketohexose. Represent both the α and β anomers of D-fructose in their cyclic furanose forms (fructofuranose). These are the starting materials.
Add the reagent ethanol (CH₃CH₂OH) and indicate the presence of a trace amount of HCl as the catalyst. The HCl will protonate the anomeric hydroxyl group, making it a better leaving group.
Show the reaction mechanism where the anomeric hydroxyl group of D-fructofuranose is protonated by HCl, leading to the formation of a carbocation at the anomeric carbon. This is followed by nucleophilic attack by ethanol on the carbocation.
Draw the products of the reaction: the α and β anomers of ethyl-D-fructofuranoside. These are formed because the nucleophilic attack by ethanol can occur from either side of the planar carbocation intermediate.
Circle the aglycone in each product. The aglycone is the non-sugar part of the glycoside, which in this case is the ethyl group (CH₃CH₂O-). Clearly label the α and β anomers in the products.
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Anomers
Anomers are a type of stereoisomer found in carbohydrates, specifically at the anomeric carbon, which is the carbon derived from the carbonyl carbon during the formation of a cyclic structure. In the case of fructose, the two anomers are designated as alpha (α) and beta (β), depending on the orientation of the hydroxyl group at the anomeric carbon. Understanding anomers is crucial for predicting the products of reactions involving sugars.
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12:58
Monosaccharides - Cyclization
Furanose and Pyranose Forms
Furanose and pyranose refer to the cyclic forms of sugars, where furanose is a five-membered ring and pyranose is a six-membered ring. Fructose can exist in both forms, but in this reaction, the furanose form is specifically mentioned. Recognizing these structures is essential for understanding how sugars react with alcohols and acids, leading to glycoside formation.
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06:23Monosaccharides - Forming Cyclic Hemiacetals
Glycoside Formation
Glycoside formation is a chemical reaction where a sugar reacts with an alcohol in the presence of an acid catalyst, resulting in the formation of a glycosidic bond. In this case, the reaction of fructose with ethanol produces ethyl-d-fructofuranoside. This concept is vital for understanding how sugars can be modified to create various derivatives, which have significant implications in organic chemistry and biochemistry.
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12:17Predict the structure of the glycoside products
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