Lactose

A reducing disaccharide built from galactose and glucose.

Formula
C12H22O11
Molar mass
342.3 g/mol
Also known as
(2R,3R,4S,5R,6S)-2-(hydroxymethyl)-6-[(2R,3S,4R,5R,6R)-4,5,6-trihydroxy-2-(hydroxymethyl)oxan-3-yl]oxyoxane-3,4,5-triol, beta-D-Lactose, beta-Lactose, D-Lactose, 4-O-beta-D-Galactopyranosyl-beta-D-glucopyranose, .beta.-Lactose, Milk sugar

Overview

A reducing disaccharide built from galactose and glucose.

Its beta glycosidic linkage joins galactose to glucose while leaving a free anomeric centre on the glucose unit. That remaining hemiacetal can equilibrate with an open-chain form. Compare lactose with sucrose to see why two sugars with the same formula can differ in reducing behaviour.

Identifiers

Formula
C12H22O11
Molar mass
342.3 g/mol
Also known as
(2R,3R,4S,5R,6S)-2-(hydroxymethyl)-6-[(2R,3S,4R,5R,6R)-4,5,6-trihydroxy-2-(hydroxymethyl)oxan-3-yl]oxyoxane-3,4,5-triol, beta-D-Lactose, beta-Lactose, D-Lactose, 4-O-beta-D-Galactopyranosyl-beta-D-glucopyranose, .beta.-Lactose, Milk sugar
Chemical identifiers
SMILES
C([C@@H]1[C@@H]([C@@H]([C@H]([C@@H](O1)O[C@@H]2[C@H](O[C@H]([C@@H]([C@H]2O)O)O)CO)O)O)O)O
InChI
InChI=1S/C12H22O11/c13-1-3-5(15)6(16)9(19)12(22-3)23-10-4(2-14)21-11(20)8(18)7(10)17/h3-20H,1-2H2/t3-,4-,5+,6+,7-,8-,9-,10-,11-,12+/m1/s1
PubChem CID
6134
Data availability

Not published: Melting Point, Boiling Point, Density, Solubility.

References

  1. PubChem Compound Summary: Lactose (CID 6134)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

  2. OpenStax Organic Chemistry: DisaccharidesJohn McMurry · OpenStax · 2023

    Supports the qualitative structural interpretation of the recorded molecular structure; no new physical measurement or verified preparative yield is claimed.