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L-malate is the malate enantiomer with $S$ configuration at its hydroxyl-bearing carbon. In the dianionic form specified here, its formula is ${\mathrm{C}}_4{\mathrm{H}}_4{\mathrm{O}}_5^{2-}$. The stereochemical label and the charge state answer separate questions: one specifies the spatial arrangement around a stereogenic carbon, while the other specifies loss of the two carboxyl protons.^[ref]

The connectivity can be written schematically asbut that flat condensed structural formula does not by itself distinguish the two enantiomers. An opposite configuration has the same elemental formula and charge. Likewise, changing protonation of a carboxyl group is not the same operation as reversing the stereochemical arrangement at the carbon bearing OH.

A metabolic transformation makes this distinction useful. The NAD-dependent oxaloacetate-forming reaction EC1.1.1.37 oxidizes L-malate to oxaloacetate while reducing NAD+ to NADH. Conversion of the hydroxyl-bearing carbon to a carbonyl removes that stereogenic center in the oxaloacetate framework. This is a covalent oxidation, rather than simply another protonation state of malate.^[ref]

A structural formula represents how chemical atoms in a molecule are connected. It adds information that a molecular formula alone does not provide. Depending on the notation, bonds and grouped atoms may be drawn explicitly or represented in a condensed structural formula.^[ref]

For ethanol, $\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{OH}$ can be unpacked as a carbon with three hydrogens, joined to a carbon with two hydrogens, joined to oxygen, joined to hydrogen. Counting the groups recovers ${\mathrm{C}}_2{\mathrm{H}}_6\mathrm{O}$, since $3+2+1=6$. That count is a useful check, but it discards the connectivity information that distinguishes ethanol from dimethyl ether, $\mathrm{C}{\mathrm{H}}_3\mathrm{OC}{\mathrm{H}}_3$.

A structural drawing also needs a clear convention about spatial meaning. A plain line usually represents a chemical bond, rather than a measured length on the page. Rotating the paper does not change the represented molecule. If a drawing is intended to specify a three-dimensional configuration, the additional conventions belong to stereochemistry; a connectivity formula should not silently be treated as complete molecular geometry.