 Methyl α-D-glucopyranoside

Methyl α-D-glucopyranoside is the α anomer of the methyl oxygen-linked glycoside derived from D-glucopyranose. Relative to the cyclic sugar, the hydroxy group at the anomeric carbon is replaced by $\mathrm{OC}{\mathrm{H}}_3$. The six-membered ring form, the D configuration and the α configuration specify different aspects of the identity.^[ref]

The name is a compact structural description. “Methyl” identifies the methyl group of the $\mathrm{OR}$ attachment; “glucopyranoside” identifies the cyclic sugar-derived part and its glycosidic substitution. The α label specifies its anomeric carbon configuration. Merely giving a molecular formula cannot recover those distinctions.

An original atom-counting example starts with glucose, ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$. Replacing $\mathrm{OH}$ by $\mathrm{OC}{\mathrm{H}}_3$ adds $\mathrm{C}{\mathrm{H}}_2$ overall, giving ${\mathrm{C}}_7{\mathrm{H}}_{14}{\mathrm{O}}_6$. Formal hydrolysis accounting isThe partner $\mathrm{C}{\mathrm{H}}_4\mathrm{O}$ is methanol, the aglycone in this example. This equation balances chemical atoms; it does not supply reaction conditions or say which glucose forms are present after a real experiment. An α-to-β configuration change would leave the elemental count unchanged.

This example distinguishes the acetal of a classical glycoside from the free cyclic sugar's hemiacetal. It is therefore a useful small molecule for learning how naming encodes more information than elemental composition.^[ref]