ANWSER
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Question 1 (a):
(i) Disaccharide that is a reducing sugar:
– Name: Maltose
– Structure: Composed of two glucose units linked by an α(1→4) glycosidic bond, with one free anomeric carbon.
(ii) Difference between epimers and anomers:
– Epimers: Diastereomers that differ in configuration at only one chiral center (e.g., D-glucose and D-mannose are C-2 epimers).
– Anomers: A subset of epimers that differ specifically at the anomeric carbon (C-1 for aldoses, C-2 for ketoses) in cyclic forms (e.g., α-D-glucopyranose and β-D-glucopyranose).
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Question 1 (b):
(i) Oxidation of galactose to galactaric acid:
– Galactose is optically active due to chiral centers. Oxidation (e.g., with HNO₃) converts both ends to carboxyl groups, creating a meso compound (galactaric acid) with a plane of symmetry, rendering it optically inactive.
(ii) Periodic acid degradation products:
– Mannose (aldose): Forms formic acid and formaldehyde (cleavage at each C-C bond with OH groups).
– Fructose (ketose): Yields two formic acid molecules and one formaldehyde.
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Question 1 (c):
(i) Optical inactivity of ribose and xylose aldaric acids:
– Both sugars yield aldaric acids with internal symmetry (meso forms) upon oxidation, canceling optical activity.
(ii) Type of sugar in raffinose:
– Trisaccharide (galactose + glucose + fructose), non-reducing due to all anomeric carbons being bonded.
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Question 1 (d):
(i) Benzaldehyde with D-glucose:
– Forms a 2,4-acetal (cyclic benzylidene derivative) due to reaction with cis-OH groups at C-2 and C-4.
(ii) Distinguishing 2-deoxyglucose from 3-deoxyglucose:
– Periodate oxidation: 2-deoxyglucose cleaves C-1–C-2 bond (no OH at C-2), while 3-deoxyglucose cleaves C-2–C-3 bond.
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Question 1 (e):
(i) Glycosides and Fehling’s/Tollen’s reagents:
– Glycosides lack a free anomeric carbon (bonded to aglycone), preventing ring opening and oxidation.
(ii) Carboxylic acid from D-glucose + HCN:
– Forms a cyanohydrin at C-1, hydrolyzed to gluconic acid (aldonic acid).
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Question 2 (a):
(i) Identical osazones for glucose, mannose, fructose:
– Osazone formation involves C-1 and C-2; these sugars differ only at C-1/C-2, which are masked by phenylhydrazone formation.
(ii) Epimerization of D-glucose:
– C-2 epimer: D-mannose
– C-3 epimer: D-allose
– C-4 epimer: D-galactose
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Question 2 (b):
(i) α-glucopyranose vs. β-isomer oxidation by HIO₄:
– α-anomer’s axial OH at C-1 and equatorial OH at C-2 are closer, facilitating rapid cleavage of the 1,2-bond.
(ii) Structural sequence for disaccharides:
– Specify linkage (e.g., α(1→4)), anomeric form, and constituent monosaccharides.
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Question 2 (c):
(i) Cellobiose vs. maltose:
– Both are glucose dimers; cellobiose has β(1→4) linkage, maltose has α(1→4).
(ii) α-D-fructopyranose (stable form):
– Six-membered ring with C-2 anomeric carbon; OH groups equatorial for stability.
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Question 2 (d):
(i) Smallest aldose forming cyclic hemiacetal:
– Glyceraldehyde (C-3) forms a 5-membered ring (unstable but possible).
(ii) Functional groups involved:
– Aldehyde (C-1) and hydroxyl (C-3) form hemiacetal.
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Question 2 (e):
(i) Products of aldobexose + Ac₂O/NaOAc:
– Peracetylated sugar (all OH esterified) and anomeric acetate (e.g., 1,2,3,4,6-penta-O-acetyl-D-glucopyranose).
(ii) Reaction with Fehling’s solution:
– No reaction; esterified OH groups prevent ring opening and oxidation.
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Question 3 (a):
Tests for metabolites:
(i) Amino acid: Ninhydrin test (purple color).
(ii) Protein: Biuret test (violet with Cu²⁺).
(iii) Alkaloid: Dragendorff’s reagent (orange precipitate).
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Question 3 (b):
(i) Protein classes:
– Simple: Albumins (e.g., serum albumin), Globulins (e.g., immunoglobulins).
– Conjugated: Glycoproteins (e.g., mucin), Lipoproteins (e.g., HDL).
(ii) Amino acid examples:
– Aliphatic unsubstituted: Glycine (H-CH(NH₂)-COOH).
– Aromatic: Phenylalanine (Ph-CH₂-CH(NH₂)-COOH).
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Question 3 (c):
Amino acid reactions:
1. Decarboxylation: R-CH(NH₂)-COOH → R-CH₂-NH₂ + CO₂.
2. Esterification: R-CH(NH₂)-COOH + R’OH → R-CH(NH₂)-COOR’ + H₂O.