Wikipedia:  

Lactose

1-beta-D-Galactopyranosyl-4-alpha-D-glucopyranose; Milk sugar; alpha-Lactose; Lactose; alpha-D-Glucopyranose, 4-O-beta-D-galactopyranosyl-; 4-O-beta-D-Galactopyranosyl-alpha-D-glucopyranose; Anhydrous lactose
Molecular Formula
C12 H22 O11
Natural Isotopic Abundance Mass
342.2964800000
Mono-Isotopic Molecular Masses
C12N14:   342.116211549
C13N14:   354.156469603
C12N15:   342.116211549
C13N15:   354.156469603
Lactose image
Lactose
InCHi String:
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

isomeric 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
canonical SMILES:
C(C1C(C(C(C(O1)OC2C(OC(C(C2O)O)O)CO)O)O)O)O


IUPAC
(2R,3S,4S,5R,6S)-2-(hydroxymethyl)-6-[(2R,3R,4S,5R,6S)-4,5,6-trihydroxy-2-(hydroxymethyl)oxan-3-yl]oxy-oxane-3,4,5-triol

IUPAC traditional
(2R,3S,4S,5R,6S)-2-methylol-6-[(2R,3R,4S,5R,6S)-4,5,6-trihydroxy-2-methylol-tetrahydropyran-3-yl]oxy-tetrahydropyran-3,4,5-triol

IUPAC cas: IUPAC openeye
(2R,3S,4S,5R,6S)-2-(hydroxymethyl)-6-[(2R,3R,4S,5R,6S)-4,5,6-trihydroxy-2-(hydroxymethyl)tetrahydropyran-3-yl]oxy-tetrahydropyran-3,4,5-triol



PubChem Substance (SID):   85164911   661460   3542
PubChem Compound (CID):   84571
KEGG: Compound ID   C00243
CAS Registry IDs:   14641-93-1
PDB Chemical Component   LBT
Miscellaneous Databases and IDs:   CHEBI 17716   EINECS 238-691-8

Reference data were obtained primarily from the PubChem database.

Three dimensional molecular rendering uses Jmol.