Lactose, known as milk sugar, consists of b-D-galactose and b-D-glucose units with a linkage between C₁ of galactose and C₄ of glucose. Lactose exhibits reducing properties as a free aldehyde group may be produced at C-1 of the glucose unit.

Maltose is composed of two a-D-glucose units, linked from C₁ of one glucose to C₄ of another. It shows reducing properties due to the free aldehyde group produced at C₁ of the second glucose unit.

Sucrose is dextrorotatory, but its hydrolysis produces dextrorotatory glucose and laevorotatory fructose. The mixture, known as invert sugar, is laevorotatory due to fructose’s higher laevorotation.

Sucrose undergoes hydrolysis to yield an equimolar mixture of D-(+)-glucose and D-(-) fructose. The glycosidic linkage is between C₁ of a-D-glucose and C₂ of b-D-fructose, involving the reducing groups and making sucrose a non-reducing sugar.

In disaccharides, reducing sugars have free aldehydic or ketonic groups, such as maltose and lactose. Non-reducing sugars, like sucrose, involve these functional groups in glycosidic bond formation.

Glycosidic linkage in disaccharides is formed by the loss of a water molecule, connecting two monosaccharide units through an oxygen atom. It results from the bonding of the reducing groups (aldehydic or ketonic) of monosaccharides.

Fructose belongs to the D-series and is a laevorotatory compound. Its open-chain structure includes a ketonic functional group at carbon number 2.

Fructose has the molecular formula C₆H₁₂O₆ and contains a ketonic functional group at carbon number 2. It shares similarities with glucose in having six carbons in a straight chain.

Fructose is obtained along with glucose by the hydrolysis of the disaccharide sucrose. It is a natural monosaccharide present in fruits, honey, and vegetables.

The existence of two crystalline forms (a and b) with different melting points (419 K and 423 K) cannot be explained by the open-chain structure (I). The proposal of a cyclic hemiacetal structure forming a six-membered ring, with —OH at ...