= 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 $\mathrm{OCH_3}$. The six-membered ring form, the D configuration and the α configuration specify different aspects of the identity.<Nomenclature of Carbohydrates (Recommendations 1996) by Alan D. McNaught>[Section2-Carb-33.1, first explicitly named structural example;33.2(a), classical names]{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>, $\mathrm{C_6H_{12}O_6}$. Replacing $\mathrm{OH}$ by $\mathrm{OCH_3}$ adds $\mathrm{CH_2}$ overall, giving $\mathrm{C_7H_{14}O_6}$. Formal <hydrolysis> accounting is
$$
\mathrm{C_7H_{14}O_6+H_2O\longrightarrow C_6H_{12}O_6+CH_4O}.
$$
The partner $\mathrm{CH_4O}$ 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.<Nomenclature of Carbohydrates (Recommendations 1996) by Alan D. McNaught>[Section2-Carb-33.1: classical mixed-acetal definition and methyl example]{ref}
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