Editing Monosaccharide (section)

===Linear-chain monosaccharides===
Simple monosaccharides have a linear and unbranched carbon skeleton with one [[carbonyl]] (C=O) [[functional group]], and one [[hydroxyl]] (OH) group on each of the remaining carbon [[atom]]s. Therefore, the molecular structure of a simple monosaccharide can be written as H(CHOH)<sub>''n''</sub>(C=O)(CHOH)<sub>''m''</sub>H, where {{nobr|''n'' + 1 + ''m'' {{=}} ''x''}}; so that its elemental formula is C<sub>''x''</sub>H<sub>2''x''</sub>O<sub>''x''</sub>.

By convention, the carbon atoms are numbered from 1 to ''x'' along the backbone, starting from the end that is closest to the C=O group. Monosaccharides are the simplest units of carbohydrates and the simplest form of sugar.

If the carbonyl is at position 1 (that is, ''n'' or ''m'' is zero), the molecule begins with a [[formyl]] group H(C=O)− and is technically an [[aldehyde]]. In that case, the compound is termed an [[aldose]]. Otherwise, the molecule has a [[ketone]] group, a carbonyl −(C=O)− between two carbons; then it is formally a ketone, and is termed a ketose. Ketoses of biological interest usually have the carbonyl at position 2.

The various classifications above can be combined, resulting in names such as "aldohexose" and "ketotriose".

A more general nomenclature for open-chain monosaccharides combines a Greek prefix to indicate the number of carbons (tri-, tetr-, pent-, hex-, etc.) with the suffixes "-ose" for aldoses and "-ulose" for ketoses.<ref name="auto">{{cite web |title=Carbohydrates |url=http://www.rsc.org/Education/Teachers/Resources/cfb/Carbohydrates.htm |access-date=10 March 2017 |website=Chemistry for Biologists |publisher=Royal Society of Chemistry}}</ref> In the latter case, if the carbonyl is not at position 2, its position is then indicated by a numeric infix.  So, for example, H(C=O)(CHOH)<sub>4</sub>H is pentose, H(CHOH)(C=O)(CHOH)<sub>3</sub>H is pentulose, and H(CHOH)<sub>2</sub>(C=O)(CHOH)<sub>2</sub>H is pent-3-ulose.