Sucrose - found in cane sugar and beet sugar - is a disaccharide - formula C12
- consisting of one glucose unit
combined with one fructose unit
The two sugars are linked (via an alpha 1,2 glycosidic bond) - effectively an oxygen bridge
- formed as a result of a condensation reaction.
bonding carbon atom numbers.
In the sucrose molecule there are 12 carbon atoms, and 2 ring-shaped structures, each containing an oxygen atom.
The glucose ring - initially on the left side - is a 6-sided structure
(5 carbons and an oxygen), whereas the fructose ring - on the right side - is a 5-sided structure
(4 carbons and an oxygen).
This structure is described as α-D-glucopyranosyl-(1→2)-β-D-fructofuranoside, by reference to pyran (a six-membered heterocyclic, ring compound, consisting of five carbon atoms and one oxygen), and furan (similar, with one less carbon atom).
The -OH groups originally on C1 of glucose and C2 of fructose which give reducing properties to the original glucose and fructose molecules have been used up in forming the bond between the two sugar units, so they cannot form reactive open-chain forms like the original sugars.
This explains why sucrose is an example of a non-reducing sugar