 Hexoses can form dihexose (like sucrose) by a condensation reaction that makes 1,6-glycosidic bond.When the carbonyl is in position 1, forming an formyl group –CH(=O), the sugar is called an aldohexose, a special case of aldose.Otherwise, if the carbonyl position is 2 or 3, the sugar is a derivative of a ketone, and is called a ketohexose, a special case of ketose; specifically, an "n"-ketohexose.