# How to draw stereochemistry: wedges, dashes and R/S labels > Use a solid wedge for a bond toward you and a hashed wedge for one pointing away, with the narrow end on the stereocenter, and leave unknown centers plain. We explain where wedges go, how CIP rules turn a drawing into R, S, E or Z, how to mark racemic and relative stereochemistry, and how to check every label in a free drawer. To draw stereochemistry, give each stereocenter a solid wedge for a bond that points toward you or a hashed wedge for one that points away, with the narrow end on the stereocenter. Draw double bonds with their real geometry, and leave a center plain when its configuration is unknown. Then check the result: [SketchIQ](/app/molecule-drawer), the free chemical structure drawer by ProteinIQ, can write R, S, E or Z next to each center as you draw, so a misplaced wedge shows up before it reaches a paper or a docking run. The check matters because R and S do not describe the drawing directly. L-serine and L-cysteine have the same configuration at their α-carbon, differ only in an oxygen that becomes a sulfur, and still get opposite labels: ```text L-serine N[C@@H](CO)C(=O)O (2S) L-cysteine N[C@@H](CS)C(=O)O (2R) ``` PubChem names them (2S)-2-amino-3-hydroxypropanoic acid and (2R)-2-amino-3-sulfanylpropanoic acid. The wedges say where the atoms are; the label comes from ranking the neighbors by the Cahn-Ingold-Prelog (CIP) rules, and sulfur outranks the carboxyl group where oxygen does not. ## What wedges, hashes and wavy bonds mean A plain line is a bond roughly in the plane of the page. IUPAC's 2006 recommendations on drawing stereochemistry give the other bond styles one meaning each. Table 1. Bond styles for stereochemistry and the SketchIQ tools that draw them. Meanings follow the IUPAC 2006 recommendations; tool names are as they appear in SketchIQ's bond menu. Source: Brecher (2006). Bond Meaning SketchIQ tool Plain line In the plane of the page; on a stereocenter with no wedge, the configuration is not specified Single Bond Solid wedge Points toward the viewer, starting from the atom at the narrow end Single Up Bond Hashed wedge Points away from the viewer, starting from the atom at the narrow end Single Down Bond Wavy line Configuration unknown, stated on purpose Single Up/Down Bond Crossed double bond Double bond geometry unknown or mixed; IUPAC does not accept it for general use, but some software still needs it Double Cis/Trans Bond The hashed wedge is the one that causes arguments. Over the years, plain hashed lines, dashed lines and hashed wedges read from either end have all meant "behind the page". IUPAC settled on a hashed wedge read like the solid one, with the narrow end on the stereocenter, and advises against bold lines in place of solid wedges. Dashed lines are best kept for what they usually mean elsewhere: hydrogen bonds, partial bonds and delocalization. ## Where to put the wedges A chemist can know a molecule's configuration perfectly and still draw it wrong, because the same wedge means different things in different places. The IUPAC recommendations boil down to a handful of rules. 1. Put the narrow end of every wedge on the stereocenter. A wedge says nothing about the atom at its wide end. 2. On a center with three drawn bonds and an implied hydrogen, draw the two plain bonds less than 180° apart and the wedge in the wide gap opposite them. A wedge squeezed into the narrow angle between the plain bonds is not acceptable for general use; bridgehead atoms are the exception. 3. On a center with four drawn bonds, the first choice is two adjacent plain bonds plus one solid and one hashed wedge. Three plain bonds and one wedge also works, as long as no two plain bonds are 180° or more apart; otherwise the drawing reads as a flat or see-saw geometry. 4. Never draw a wedge between two stereocenters. Readers cannot tell which center it is meant for, so wedge a bond to a non-stereogenic neighbor or to a hydrogen instead. 5. Leave the hydrogen on a stereocenter implicit only when the drawing stays unambiguous. Drawing it is always acceptable. 6. Draw bonds to atoms that are not stereocenters as plain lines. A wedge on an achiral carbon adds nothing and can mislead software that reads it. Software reads the first rule literally. In SketchIQ, a wedge on alanine's carbon-nitrogen bond with the narrow end on the α-carbon gives D-alanine, labeled (R). Flip the same wedge so its narrow end sits on the nitrogen and the panel reports `1 (1 undefined)`: the drawing has stopped saying anything about the stereocenter. IUPAC also warns against writing R or S on a drawing instead of wedging it. A label alone makes every reader apply the CIP rules correctly before they know what the molecule looks like. Labels belong next to wedges, as a check, not in place of them. ## How to draw a stereocenter in SketchIQ SketchIQ runs in the browser and needs no account for drawing. The bond tools come from Ketcher, the open-source editor it is built on, so the steps match other Ketcher-based editors. 1. Draw the skeleton with plain bonds, or type a name or SMILES into the search box above the canvas. 2. Click the small triangle on the **Single Bond** button in the left toolbar and choose **Single Up Bond** for a solid wedge or **Single Down Bond** for a hashed wedge. 3. Click the bond you want to wedge. 4. Open SketchIQ settings (the sliders button beside **Export**) and turn on **Show R/S and E/Z on the canvas**. 5. Read the label next to the stereocenter. If none appears, click the wedge again: each click swaps which end is narrow. The panel beside the canvas repeats the result. **Stereocentres** counts every stereocenter and how many are undefined, and **Stereo** lists each R, S, E and Z label with whether the stereochemistry is absolute, racemic or relative. The labels come from RDKit running in your browser, and the canvas labels are an overlay, so exported files and images leave them out. ![SketchIQ with ephedrine on the canvas, the labels R and S next to its two stereocenters, and the details panel showing two stereocenters and the stereo line S, R absolute](/images/guides/stereochemistry-wedges-dashes/ephedrine-labels.webp '**Figure 1. Ephedrine in SketchIQ with R/S labels turned on.** Each label sits beside its stereocenter; the Stereo row in the panel lists the same two.') The panel lists labels in the order the atoms are stored, not by locant. For ephedrine, PubChem's name is (1R,2S)-2-(methylamino)-1-phenylpropan-1-ol, while the panel shows `S, R`. Use the canvas labels when you need to know which center is which. ## How R and S are assigned CIP rules give each stereocenter a label from its three-dimensional arrangement and a ranking of its four neighbors. Done by hand, it takes four steps. 1. Rank the four atoms bonded to the stereocenter by atomic number. Higher wins: Br > Cl > S > O > N > C > H. 2. Break ties by moving outward. For each tied neighbor, list the atoms attached to it, hydrogens included, other than the stereocenter, highest first, compare the lists and stop at the first difference. A double bond counts its partner twice, so C=O looks like a carbon carrying two oxygens. 3. Turn the molecule so the lowest-ranked neighbor, often hydrogen, points away from you. 4. Trace 1 → 2 → 3. Clockwise is R and anticlockwise is S. If the lowest-ranked group is on a solid wedge, pointing at you, read the direction and reverse it. Cysteine shows why step 2 matters. Its stereocenter carries NH₂, COOH, CH₂SH and H. Nitrogen ranks first. COOH and CH₂SH both start with carbon, so the tie is broken one atom out: COOH carries {O, O, O} and CH₂SH carries {S, H, H}. Sulfur beats oxygen at the first point of difference, so CH₂SH ranks second. In serine the same position carries {O, H, H}, which loses to {O, O, O}. Swapping ranks 2 and 3 reverses the label without moving an atom. Table 2. CIP rankings and labels for five drug and amino acid stereocenters. Labels were calculated with RDKit in SketchIQ and match the PubChem IUPAC names. Sources: PubChem (2026). Compound Center Neighbors ranked 1 to 4 Label L-serine C2 NH₂ > COOH > CH₂OH > H S L-cysteine C2 NH₂ > CH₂SH > COOH > H R Dexibuprofen C2 COOH > aryl > CH₃ > H S Ephedrine C1, C2 C1: OH > C2 > phenyl > H; C2: NHCH₃ > C1 > CH₃ > H 1R, 2S Pseudoephedrine C1, C2 Same rankings as ephedrine 1S, 2S At ephedrine's C1, the C2 carbon beats the phenyl ring even though the ring is bigger, because C2 carries a nitrogen and the ring's first carbon carries only carbons. Pseudoephedrine differs from ephedrine at C1 alone, which makes the two diastereomers rather than mirror images. The CIP rules have hard corners, such as ring systems where the same atoms are reached by several paths, and centers whose neighbors differ only in their own stereochemistry. In 2018 an international team of cheminformatics developers found flaws in two of the sequence rules as IUPAC wrote them in 2013, proposed fixes and published a 300-compound validation suite for software. Every label in this guide agrees between SketchIQ, a separate RDKit install and PubChem's names; for an unusual polycyclic, compare two tools before trusting one. ## How to draw E and Z double bonds A double bond needs no wedges. Draw the substituents where they are, and the geometry is the stereochemistry. The label comes from the same CIP ranking, applied separately at each end of the bond: if the higher-ranked groups on the two carbons are on the same side, the bond is Z (zusammen); on opposite sides, it is E (entgegen). E and Z are not cis and trans. In 2-bromobut-2-ene drawn with its two methyl groups on the same side, the bond looks cis, but bromine outranks methyl on C2, and it sits opposite the methyl on C3. PubChem names that isomer (E)-2-bromobut-2-ene, and SketchIQ labels it E. The breast cancer drug tamoxifen is the Z isomer, named 2-[4-[(Z)-1,2-diphenylbut-1-enyl]phenoxy]-N,N-dimethylethanamine. ![SketchIQ with 2-bromobut-2-ene drawn with both methyl groups on the same side of the double bond and the label E on the bond](/images/guides/stereochemistry-wedges-dashes/bromobutene-e.webp '**Figure 2. (E)-2-bromobut-2-ene in SketchIQ.** The two methyls are cis, but the higher-ranked groups, Br and the C3 methyl, are on opposite sides.') When the geometry of a double bond is unknown, IUPAC prefers drawing the substituent in line with the double bond or with a wavy bond. It does not accept the crossed double bond for general use, although some databases and file formats still need it. RDKit, and so SketchIQ, labels a ring double bond E or Z only in rings of eight or more atoms; in smaller rings such as cyclohexene it is taken as cis and gets no label. ## Undefined, racemic and relative stereocenters A stereocenter drawn with plain bonds is undefined: the drawing makes no claim about its configuration. It is also how PubChem stores the racemates we checked. When we drew ibuprofen with plain bonds, SketchIQ reported `1 (1 undefined)` and matched it to PubChem's racemic ibuprofen, CID 3672, while the (S)-enantiomer, dexibuprofen, is a separate record, CID 39912. Drawing DL-alanine and L-alanine gives the same split. Plain bonds cannot tell "unknown" apart from "a known mixture of both enantiomers". Enhanced stereochemistry fills that gap: a group label on one or more stereocenters changes what the wedges mean. Table 3. Enhanced stereochemistry labels. SketchIQ shows the stereo type in the Stereo row and keeps the group in extended SMILES. Sources: Certara (2026), SketchIQ. Label Meaning Typical use SketchIQ Stereo row ABS The configuration is exactly as drawn A single, characterized enantiomer S · absolute AND A mixture of the drawn configuration and its mirror image A racemate made from achiral starting materials S · racemic (AND) OR One configuration, either the drawn one or its mirror image, not known which One enantiomer separated by chiral chromatography before its absolute configuration was assigned S · relative (OR) To add a group in SketchIQ, draw one enantiomer with wedges, select the stereocenters, click **Stereochemistry** in the left toolbar (or press `Alt+E`), choose **Create new AND Group** or **Create new OR Group**, and click **Apply**. The canonical SMILES in the panel then carries the group in extended SMILES notation, for example `C[C@H](N)C(=O)O |&1:1|` for racemic alanine, where `&1:1` puts atom 1 (counting from 0) in AND group 1, and `o1` would mark an OR group. ![SketchIQ with ibuprofen drawn with a hashed bond to its methyl group, labeled S, and the details panel showing S racemic AND and a canonical SMILES ending in &1:8](/images/guides/stereochemistry-wedges-dashes/ibuprofen-and.webp '**Figure 3. Racemic ibuprofen drawn as an AND group.** The (S) label belongs to the enantiomer on the canvas; the group says its mirror image is present too.') Two things surprise people here. The R or S label on an AND or OR center still describes the enantiomer you drew, not the mixture, so racemic ibuprofen drawn this way shows (S) on the canvas. And standard InChI has no AND or OR, so SketchIQ switches to a non-standard InChIKey that keeps the group, and PubChem, which indexes standard keys, no longer finds the compound. With two or more stereocenters, AND and OR describe relative configuration. Racemic trans-1,2-dimethylcyclohexane is the (1R,2R) and (1S,2S) pair, and one AND group over both centers says exactly that. IUPAC notes that no drawing convention for relative configuration has won general acceptance, and calls drawing each isomer separately, with explanatory text if needed, the safest approach. In names and captions, the prefixes rac- and rel- do the same job: rac-(1R,2R) for the racemate, rel-(1R,2R) for one isomer of known relative but unknown absolute configuration. A meso compound needs no group at all. meso-Tartaric acid has two stereocenters, (2R,3S), and an internal mirror plane, so the drawing with two wedges is already one achiral compound. ## Common stereochemistry drawing mistakes Table 4. Drawing mistakes that change or erase stereochemistry. Symptoms are what SketchIQ shows. Source: Brecher (2006). Mistake What you see Fix Wedge drawn backwards, wide end on the stereocenter No label; the Stereocentres row shows 1 (1 undefined) Click the wedge again to flip it Wedge between two stereocenters A label appears, but readers may assign the wedge to the other center Move the wedge to a bond from the stereocenter to a non-stereogenic atom Wedge on the bond to the lowest-ranked group, read as if it pointed away Your hand assignment disagrees with the label Reverse your answer when the lowest-ranked group points toward you Calling a cis double bond Z The label says E Rank each end by CIP rules; heavy atoms such as Br, Cl or S often flip the answer Wedges drawn on a racemate Panel says absolute; database lookups find one enantiomer Use plain bonds, or add an AND group Wedges added to make a figure look 3D Labels or stereocenter counts that don't match the compound Keep wedges for real stereocenters; use a 3D viewer for shape ## After the drawing Stereochemistry that is right on the page has to survive the next step. [SMILES](/guides/smiles-notation) keeps it as `@`, `@@`, `/` and `\`, and MOL V3000 and extended SMILES keep AND and OR groups, while MOL V2000 cannot; the [chemical file formats](/guides/chemical-file-formats) guide compares what each format holds, and [InChI and InChIKey](/guides/inchi-inchikey-smiles-cas) explains why their stereo layers matter for database searches. Docking needs one 3D structure per stereoisomer. If a drawing still has undefined centers, the [stereoisomer generator](/app/stereoisomer-generator) lists every isomer as its own SMILES, and [SMILES to SDF](/app/smiles-to-sdf) builds 3D coordinates that keep the configuration you drew. From SketchIQ, the **Use this molecule in** list sends the structure straight to [AutoDock Vina](/app/autodock-vina), which the [drawing to docking](/guides/drawing-to-docking) guide walks through, and [publication-quality images](/guides/publication-quality-chemical-structures) covers getting the same drawing onto a slide or into a paper. ## Frequently asked questions ### What is the difference between a wedge and a dash in chemistry? A solid wedge is a bond pointing toward you and a hashed wedge, often called a dash, is a bond pointing away, both starting at the narrow end. IUPAC recommends hashed wedges over plain dashed lines, which are also used for hydrogen bonds. ### Does R mean clockwise on the drawing? Only when the lowest-ranked group points away from you. If it sits on a solid wedge, the direction you see is reversed, so clockwise on the page means S. ### Is R the same as D, or S the same as L? No. D and L compare a molecule with glyceraldehyde, and R and S come from CIP rankings. Most L-amino acids are S, but L-cysteine is R because its sulfur changes the ranking. The sign of optical rotation, (+) or (−), is measured and follows neither. ### Do I need a wedge on every stereocenter? On every stereocenter whose configuration you know, yes, and one wedge per center is usually enough. Leave centers plain when the configuration is unknown or the sample is racemic, unless you add an AND group. ### How do I show a racemic mixture in a structure drawing? Draw plain bonds, which is how PubChem stores racemic ibuprofen, or draw one enantiomer and put its stereocenters in an AND group. In text, add rac- before the descriptors.