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Which one of the following does not exhibit the phenomenon of mutarotation?
A
(–) Fructose
B
(+) Sucrose
C
(+) Lactose
D
(+) Maltose
Detailed Solution
Mutarotation is the change in specific rotation of a sugar solution with time; it needs a free hemiacetal or hemiketal (anomeric –OH) group so that the ring can open and re-close to interconvert the α and β forms.
Fructose (a monosaccharide), maltose and lactose (reducing disaccharides) all have a free anomeric –OH group, so they show mutarotation.
In sucrose, C-1 of α-D-glucose is linked to C-2 of β-D-fructose; both anomeric carbons are used up in the glycosidic bond.
So sucrose has no free hemiacetal or hemiketal group; it is a non-reducing sugar and cannot show mutarotation.
Hence (+) sucrose does not exhibit mutarotation.
Fructose (a monosaccharide), maltose and lactose (reducing disaccharides) all have a free anomeric –OH group, so they show mutarotation.
In sucrose, C-1 of α-D-glucose is linked to C-2 of β-D-fructose; both anomeric carbons are used up in the glycosidic bond.
So sucrose has no free hemiacetal or hemiketal group; it is a non-reducing sugar and cannot show mutarotation.
Hence (+) sucrose does not exhibit mutarotation.