Sacarid — Carbohydrate Chemistry | sacarid.com
Which sugars pair up into which disaccharide, with formulas and molar masses.
Monosaccharides are single sugar rings with the formula C6H12O6 and a molar mass of 180.16 g/mol. The three common ones are glucose, fructose and galactose. They are isomers: same atoms, same mass, different arrangement.
Disaccharides are two monosaccharide units joined by a glycosidic bond, with the formula C12H22O11 and a molar mass of 342.30 g/mol. Sucrose is glucose plus fructose; lactose is glucose plus galactose; maltose is glucose plus glucose.
When two monosaccharides condense into a disaccharide, one water molecule is expelled. That is why the disaccharide mass is not simply twice the monosaccharide mass: 2 × 180.16 = 360.32 g/mol before condensation, 342.30 g/mol after.
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The pairing rule is worth memorising because it explains the formula. Any disaccharide in this family loses one water relative to its two component rings, and that single loss is what turns C6H12O6 into C12H22O11 rather than C12H24O12.
Maltose, being glucose plus glucose, is the only one of the three disaccharides made from two identical units. Sucrose and lactose each combine two different monosaccharides, which is why their behaviour in the body differs from maltose even though all three share a molar mass.
For classification purposes, the formula is enough: six carbons means a single ring; twelve carbons means two rings joined. The molar mass follows directly.
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