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Fructose is found in many fruits. From memory, draw fructose in

  1. the Fischer projection of the open chain.
  2. The most stable chair conformation of the most stable pyranose anomer.
  3. The Haworth projection of the most stable pyranose anomer

Short Answer

Expert verified

Fructose is a ketohexose which contain a ketone group. It is used as a sweetening agent in many confectionaries and also as a substitute of cane sugar.

Step by step solution

01

Fructose

Fructose is a ketohexose which contain a ketone group. It is used as a sweetening agent in many confectionaries and also as a substitute of cane sugar.

02

Pyranose

Pyranose is a six-membered cyclic hemiacetal whose name is derived from the six-membered cyclic ether pyran.

03

Anomers

The diastereomers resulting from cyclisation are known as anomers. They differ only in the configuration around first carbon (C1) which is referred to as the anomeric carbon (hemiacetal carbon atom).

04

Identifying α  and β  anomers of pyranoses

For 伪-anomer, hydroxy group (-OH) on the anomeric carbon is down (axial position) while for 尾 - anomer, hydroxy group (-OH) on the anomeric carbon is up (equatorial position). Again, for anomer, the anomeric hydroxy (-OH) group is placed trans to the terminal -CH2OH group while for 尾- anomer, the anomeric hydroxy (-OH) group is placed cis to the terminal -CH2OH group.

05

 Step 5: Structure of various forms of fructose

a) Sugars in their open chain form is given by the Fischer projection where the vertical solid lines show the connection of different carbon atoms present in a sugar while the horizontal solid lines show carbon-oxygen and carbon- hydrogen bonds.


b) The most stable chair conformation of the most stable pyranose anomer of fructose is 尾-D- fructopyranose . In chair conformation of 尾-D- fructopyranose , the anomeric carbon is C1 . The hydroxy group ( -OH ) on the anomeric carbon is up (equatorial position).

c) The Haworth projection of 尾-D- fructopyranose is represented by the figure below:


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Most popular questions from this chapter

a) Draw D-allose, the C3 epimer of glucose.

b) Draw D-talose, the C2 epimer of D-galactose.

c) Draw D-idose, the C3 epimer of D-talose. Now compare your answers with Figure 23-3.

d) Draw the C4 鈥渆pimer鈥 of D-xylose. Notice that this 鈥渆pimer鈥 is actually an L-series sugar, and we have seen its enantiomer. Give the correct name for this L-series sugar.

Trehalose is a nonreducing disaccharide (C12H22O11) isolated from the poisonous mushroom Amanita muscaria. Treatment with an 伪 -glucosidase converts trehalose to two molecules of glucose, but no reaction occurs when trehalose is treated with a 尾 -glucosidase. When trehalose is methylated by dimethyl sulfate in mild base and then hydrolyzed, the only product is 2,3,4,6-tetra-O-methylglucose. Propose a complete structure and systematic name for trehalose.

Question: Propose a mechanism for methylation of any one of the hydroxy groups of methyl--D-glucopyranoside,using and dimethyl sulfate.

Like glucose, galactose mutarotates when it dissolves in water. The specific rotation of -D-galactopyranoseis +150.70 , and that of the anomer is +52.80 . When either of the pure anomers dissolves in water, the specific rotation gradually changes to +80.20. Determine the percentages of the two anomers present at equilibrium.

H. G. Khorana won the Nobel Prize in Medicine in 1968 for developing the synthesis of DNA and RNA and for helping to unravel the genetic code. Part of the chemistry he developed was the use of selective protecting groups for the 5鈥 OH group of nucleosides.

The trityl ether derivative of just the 5鈥 OH group is obtained by reaction of the nucleoside with trityl chloride, MMT chloride, or DMT chloride and a base like Et3N. The trityl ether derivative can be removed in dilute aqueous acid. DMT derivatives hydrolyze fastest, followed by MMT derivatives, and trityl derivatives slowest.

(a) Draw the product with the trityl derivative on the 5鈥 oxygen.

(b) Explain why the trityl derivative is selective for the 5鈥 OH group. Why doesn鈥檛 it react at 2鈥 or 3鈥? (c) Why is the DMT group easiest to remove under dilute acid conditions? Why does the solution instantly turn orange when acid is added to a DMT derivative?

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