= Chemical structure
A \b[chemical structure] specifies how <chemical atoms> are connected and, where relevant, how they are arranged in space. A <molecular formula> counts atoms; a <structural formula> supplies connectivity information. <Molecular geometry> and <stereochemistry> add spatial distinctions that cannot generally be recovered from the atom inventory alone.<IUPAC Compendium of Chemical Terminology, fifth edition (Gold Book) by International Union of Pure and Applied Chemistry>[Entry S06061, structural formula: information on how atoms in a molecule are connected; DOI 10.1351/goldbook.S06061.]{ref}
For a concrete comparison, <ethanol> and <dimethyl ether> both have <molecular formula> $\mathrm{C_2H_6O}$. Their condensed <structural formulas> are
$$
\mathrm{CH_3CH_2OH}\qquad\text{and}\qquad\mathrm{CH_3OCH_3},
$$
respectively. In <ethanol>, the <oxygen> is bonded to one <carbon> and one <hydrogen>; in <dimethyl ether>, it is bonded to two <carbon> atoms. The same atom counts therefore describe different connectivities.
A drawing is a representation of a <chemical structure>, not necessarily a frozen picture of every atom's position. Rotating around a bond can change a <molecule>'s spatial arrangement while preserving its connectivity. Conversely, two drawings that look different on the page can represent the same <chemical structure>. Establishing identity requires interpreting bonds and spatial conventions, not comparing the appearance of the diagrams alone.
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