= Dimethyl ether
\b[Dimethyl ether], also called methoxymethane, is an <ether> with an <oxygen> atom bonded to two <methyl groups>. Its <structural formula> is $\mathrm{CH_3-O-CH_3}$ and its <molecular formula> is $\mathrm{C_2H_6O}$. It is a <constitutional isomer> of <ethanol>: the atoms have the same inventory but different connectivity.<Dimethyl ether in ChEBI>[CHEBI:28887, Definition, structure, Formula and Synonyms.]{ref}
The oxygen connectivity gives a useful molecular comparison. <Ethanol> contains an oxygen–hydrogen bond; <dimethyl ether> does not. Thus the two <chemical structures> present different possibilities for <hydrogen bonding>, even though weighing equal numbers of their molecules would not distinguish their common elemental formula.
Their physical identity can be tested by measurements beyond composition. NIST tabulates a normal <boiling point> near $248.3\,\mathrm{K}$, approximately $-24.9\,{}^{\circ}\mathrm{C}$, for <dimethyl ether>. This illustrates why a small carbon-containing molecule can be a gas under ordinary room conditions: phase behavior follows its interactions and external conditions, rather than molecular formula alone.<NIST Chemistry WebBook, SRD 69>[Dimethyl ether, CAS115-10-6, Phase change data: boiling-point compilation near248.2–248.3K; record C115106.]{ref}
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