Lactose (milk sugar) is a disaccharide - formula C
12H
22O
11 - consisting of one
galactose unit and one
glucose unit, combined.
The two sugars are linked via a glycosidic bond - a
beta 1-4 bond between galactose and glucose.
This bond - effectively an oxygen bridge - is formed as a result of a
condensation reaction.
Label
/
unlabel bonding carbon atom numbers.
Note that one of these ring-shaped sections (glucose) is in equilibrium with an
open-chain form in which Carbon 1 has a CHO aldehyde group which gives it
reducing properties, so that it reacts with reagents such as Benedict's.