The diagram shows a molecule of the simple carbohydrate fructose. Atoms and a group of atoms which are constituents of the molecule are labelled P, Q and R.Molecules of glucose and fructose can react to form a disaccharide.Which constituent of fructose participates in the reaction with glucose, and what bond is formed?

Question

BlackTom AI · Accepted Answer

First, let's analyze the question: when glucose and fructose combine to form a disaccharide, what part of fructose is involved and what type of bond is created?
Option a: 'Constituent P forms an ether linkage.' If P were the anomeric carbon of glucose, the linkage would still be a glycosidic (ether) bond, but the statement specifies P forms the ether linkage rather than identifying the correct reacting group on fructose. This makes the option suspect unless P is the anomeric carbon of glucose; in many diagrams P does not represent the reacting anomeric carbon of fructose, so this option is not reliably correct.
Option b: 'Constituent Q forms an ester linkage.' An ester linkage would involve a carboxylate-derived group, which is not how monosaccharides link in standard glycosidic bonds to form disaccharides like sucrose. Therefore this is chemically incorrect for the glucose-fructose condensation.
Option c: 'Constituent R forms an ether linkage.' In the formation of sucrose, the two anomeric carbons (the C1 of glucose and the C2 of fructose) come together, producing a glycosidic bond, which is an ether linkage. This correctly identifies both the reacting partner on fructose (its anomeric carbon) and the type of bond formed (glycosidic ether linkage).
Option d: 'Any of constituents P, Q or R form an ester linkage.' This implies flexibility of which part can participate and also claims an ester bond, which is incorrect because glycosidic bonds in disaccharides are ether linkages, not esters, and typically only specific anomeric carbons participate to form the correct linkage.
In summary, the correct mechanistic detail is that the anomeric carbon of fructose participates in the reaction with glucose to form a glycosidic (ether) bond, i.e., a C–O–C glycosidic linkage. The option that states this precisely is option c, while the others either misidentify the reacting group or misname the bond type.

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