Dimethyl ether

Dimethyl ether, also called methoxymethane, is an ether with an oxygen atom bonded to two methyl groups. Its structural formula is $\mathrm{C}{\mathrm{H}}_3-\mathrm{O}-\mathrm{C}{\mathrm{H}}_3$ and its molecular formula is ${\mathrm{C}}_2{\mathrm{H}}_6\mathrm{O}$. It is a constitutional isomer of ethanol: the atoms have the same inventory but different connectivity.^[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.^[ref]