Concept explainers
Interpretation:
The structures of
Concept introduction:
舧 A carbohydrate is a
舧
舧 Carbohydrates are oxidized by
舧 Aldaric acids are carbohydrates having two
舧 The molecules that are nonsuperimposable or not identical with their mirror images are known as chiral molecules.
舧 A pair of two mirror images that are nonidentical is known as enantiomers, which are optically active.
舧 The stereoisomers that are nonsuperimposable on each other and not mirror images of each other are known as diastereomers.
舧 The achiral compounds in which plane of symmetry is present internally and consists of chiral centres are known as meso compounds, but they are optically inactive.
舧 Compounds that have a plane of symmetry tend to exist in meso forms. A meso form arises when the two stereoisomers produce superimposable images, and hence, compounds having meso forms are optically inactive.
舧 The Kiliani-Fischer reaction is used for increasing the number of carbon atoms of respective aldoses, thereby, lengthening the carbon chain of the compound. It is used to produce epimers of higher aldoses from a lower aldose, i.e., an aldose with a lesser number of carbon atoms produces a mixture having two epimeric aldoses with a higher number of carbon atoms.
舧 Oxidation of aldoses by nitric acid produces optically inactive aldaric acids. This is due to the formation of meso compounds. Compounds that do not form meso structures are optically active.
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Organic Chemistry
- Regarding 4-O- (α-D-psychofuranosyl) -β-D-allopyranose. Please indicate the RIGHT alternative: (a) The disaccharide reacts with CH3OH in an acid medium to form a glycoside that cannot be oxidized with HNO3. (b) It is a reducing disaccharide only in basic medium. (c) In the structure there is only one glycosidic bond that is of the type β 1-O-4 ' (d) The hydrolysis products of this disaccharide do not show mutarrotation. (e) The disaccharide structure contains two six-membered rings.arrow_forwardWhich of the following are reducing sugars? Comment on the common name sucrosefor table sugar.(a) methyl a-d-galactopyranoside (b) b-l-idopyranose (an aldohexose)(c) a-d-allopyranose (d) ethyl b-d-ribofuranosidearrow_forwardA D-aldopentose A is reduced to an optically active alditol. Upon Kiliani–Fischer synthesis, A is converted to two D-aldohexoses, B and C. B is oxidized to an optically inactive aldaric acid. C is oxidized to an optically active aldaric acid. What are the structures of A–C?arrow_forward
- A D-aldopentose A is oxidized to an optically inactive aldaric acid with HNO3. A is formed by the Kiliani–Fischer synthesis of a D-aldotetrose B, which is also oxidized to an optically inactive aldaric acid with HNO3. What are the structures of A and B?arrow_forwardWhich D-aldopentoses are reduced to optically inactive alditols using NaBH,, CH;OH?arrow_forwardCompound Z is an aldopentose. If Z is oxidized with nitric acid the product is optically active. If Z undergoes one Ruff degradation and the product of that degradation is reduced to the alditol using H2/Ni the resulting product is optically inactive. If compound Z undergoes two Ruff degradations, D-glyceraldehyde (shown below) is obtained. Draw the usual Fischer projection of Z (aldehyde at the top). (Hint: work backwards from D- glyceraldehyde.)arrow_forward
- There are three (3) vials labeled A, B, and C known to contain the following monosaccharides. All three samples reduce Tollens and Fehling. By oxidation with dilute HNO3 an optically active aldaric acid is obtained for sample A and the remaining two give products without optical activity. When the three samples were subjected to an alkaline medium, it was observed that, after a certain time, samples A and C reached the same value of the specific rotation [α]. Select the RIGHT alternative: (a) Sample A is Galactose. (b) Sample B is Alosa. (c) Samples A and C are not related to each other by an epimerization process. (d) Sample C is Talose. (e) Samples B and C are epimers.arrow_forwardA D-aldohexose A is formed from an aldopentose B by the Kiliani-Fischer synthesis. Reduction of A with NABH4 forms an optically inactive alditol. Oxidation of B forms an optically active aldaric acid. What are the structures of A and B?arrow_forwardThe anticoagulant heparin is a polysaccharide that contains alternating residues of -D- glucuronic acid-6- sulfate and N-sulfo-D-glucosamine-6sulfate connected by (1 B 4)- glycosidic linkages. Draw a part of heparin that shows one each of the two residues.arrow_forward
- Monosaccharide A is a D-aldotetrose. Treatment of A with nitric acid gives an optically inactive aldaric acid (B). Killiani-Fischer chain extension of A gives two products (C & D). C on treatment with NABH4, gives an alditol (E) that is optically active. D gives an alditol (F) that is NOT optically active. Give Fischer projections for A, B, CD, E, and E.arrow_forwarda) The D-aldopentose A, C5H1005, reacts with HNO3 to yield an optically active aldaric acid B. Kiliani-Fischer chain extension of A produces a pair of D-aldohexoses C and D. C is converted by HNO3 to an optically active aldaric acid, but D is converted by HNO3 to an optically inactive aldaric acid. Write acyclic Fischer projections for A, B, C, D.arrow_forwarda) The D-aldopentose A, C5H1005, reacts with HNO3 to yield an optically active aldaric acid B. Kiliani-Fischer chain extension of A produces a pair of D-aldohexoses C and D. C is converted by HNO3 to an optically active aldaric acid, but D is converted by HNO3 to an optically inactive aldaric acid. Write acyclic Fischer projections for A, B, C, D. b) Disaccharide E is a reducing sugar. It is hydrolyzed by an α-glycosidase enzyme, which means it contains an α- glycoside link. Treatment of E with Ag2O and excess Mel gives an octamethyl derivative F. Hydrolysis of F in dilute aqueous acid gives the pair of molecules shown below. Write the structures of E and F. (If the stereochemistry at a particular carbon is not determined by the above data, indicate this with a wavy line as shown below.) HO OMe OMe MeO MeO MOH OMe mOH OMe OMearrow_forward
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