Organic Chemistry
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The cyclization of ribulose is shown below. Propose a mechanism for this cyclization, assuming a small amount of acid is present.
The brief treatment of a D-hexanose with a dilute base causes the isomerization of its carbonyl. The product is the C3 epimer of D-fructose. What is the structure of the furanose product?
Draw the structure(s) of the cyclic hemiacetal formed by the 4-hydroxyaldehyde, 4-hydroxyhexanal.
Draw the structure(s) of the cyclic hemiacetal formed by the 5-hydroxyaldehyde, 5-hydroxyhexanal.
Provide the structure(s) of the cyclic hemiacetal formed by the 4-hydroxyaldehyde, 4-hydroxy-5-methylhexanal.
Mannose is the C2 epimer of glucose. Illustrate the structure of ethyl β-D-mannopyranoside.
Predict the plausible structure of ethyl α-D-arabinofuranoside. Note: Ribose is the C2 epimer of arabinose.
Propose the plausible structure of β-D-galactopyranose. Note: Galactose is the C4 epimer of glucose.
Fructose, a sugar commonly found in fruits, can also exist in open-chain and cyclic hemiketal forms. If a small amount of acid is present, propose the mechanism for the cyclization of fructose. Ignore stereochemistry in the mechanism.
Galactose, a monosaccharide component of lactose found in milk, exists predominantly in its cyclic form rather than its open-chain form. Would an aqueous solution of galactose give a positive Fehling's test? Justify your answer.
Sketch out a cyclic structure for α-D-ribofuranose.
Sketch out a cyclic structure for α-D-tallopyranose (the C2 epimer of galactose).
Provide the chair conformation of N-acetylgalactosamine. Hint: Start with the structure of α-D-galactopyranose and replace the —OH at C2 with an acetylated amino group.