Draw the expected product of the reaction of the following sugars with excess methyl iodide and silver oxide.

  1. α-D-fructofuranose
  2. β-D-galactopyranose

Short Answer

Expert verified
  1. methyl 2,3,4,6,-tetra-O-methyl-α-D-fructofuranoside
  2. methyl 2,3,4,6,-tetra-O-methyl-β-D-fructofuranoside


Step by step solution

01

Formation of methyl ether

Hydroxy groups of sugar can be converted to methyl ethers by treating with methyl iodide (CH3I) and silver oxide (Ag2O). CH3-I group can be polarised by silver oxide (Ag2O), which makes the methyl carbon more strongly electrophilic. Attack by the -OH group of carbohydrate is then followed by deprotonation which gives the ether.

02

Pyranose and furanose

Pyranose is a six-membered cyclic hemiacetal while a furanose is a five-membered cyclic hemiacetal.

03

Formation of product

  1. α-D-fructofuranose on treatment with excess methyl iodide and silver oxide gives methyl 2,3,4,6, -tetra-O-methyl-α-D-fructofuranoside as the product.
  2. β-D-galactopyranose on treatment with excess methyl iodide and silver oxide gives methyl 2,3,4,6,-tetra-O-methyl-β-D-galactopyranoside as the product.

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Most popular questions from this chapter

Emil Fischer synthesized L-gulose, an unusual aldohexose that reduces to give D-glucitol. Suggest a structure for this L sugar, and show how L-gulose gives the same alditol as D-glucose. (Hint: D-Glucitol has -CH2OHgroups at both ends. Either of these primary alcohol groups might have come from reduction of an aldehyde.)

Cytosine, uracil and guanine have tautomeric forms with aromatic hydroxyl groups. Draw these tautomeric forms.

Draw the structures (using chair conformations of pyranoses) of the following disaccharides.

(a) 4-O-(α -D-glucopyranosyl)-D-galactopyranose

(b) α -D-fructofuranosyl-β -D-mannopyranoside

(c) 6-O-(β -D-galactopyranosyl)-D-glucopyranose

(a) Which of the D-aldopentoses will give optically active aldaric acids on oxidation with HNO3 ?

(b) Which of the D-aldotetroses will give optically active aldaric acids on oxidation withHNO3 ?

(c) Sugar X is known to be a D-aldohexose. On oxidation with HNO3 , X gives an optically inactive aldaric acid. When X is degraded to an aldopentose, oxidation of the aldopentose gives an optically active aldaric acid. Determine the structure of X.

(d) Even though sugar X gives an optically inactive aldaric acid, the pentose formed by degradation gives an optically active aldaric acid. Does this finding contradict the principle that optically inactive reagents cannot form optically active products?

(e) Show what products results if the aldopentose formed from degradation of X is further degraded to an aldotetrose. DoesHNO3 oxidize this aldotetrose to an optically active aldaric acid?

Raffinose is a trisaccharide (C18H32O16) isolated from cottonseed meal. Raffinose does not reduce Tollens reagent, and it does not mutarotate. Complete hydrolysis of raffinose gives D-glucose, D-fructose, and D-galactose. When raffinose is treated with invertase, the products are D-fructose and a reducing disaccharide called melibiose. Raffinose is unaffected by treatment with a-galactosidase, but an α -galactosidase hydrolyzes it to D-galactose and sucrose. When raffinose is treated with dimethyl sulfate and base followed by hydrolysis, the products are 2,3,4-tri-O-methylglucose, 1,3,4,6-tetra-O-methylfructose, and 2,3,4,6-tetra-O-methylgalactose. Determine the complete structures of raffinose and melibiose and give a systematic name for melibiose.

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