--- title: "Chirality & R/S Worksheet with Answers (Free PDF) | MolDraw" url: https://www.moldraw.com/educational-materials/chirality-rs-worksheet/ description: "Chirality worksheet with answers: find stereocentres and assign R or S configuration with CIP rules for alanine, lactic acid, ibuprofen, thalidomide and more." lang: en publisher: Scidart Academy generated: 2026-10-28 --- [MolDraw](https://www.moldraw.com/) › [Educational materials](https://www.moldraw.com/educational-materials/) › Chirality & R/S Configuration Worksheet # Chirality & R/S Configuration Worksheet Organic chemistryGrades 11–12 · A-level / IB · AP Chemistry · CBSE/JEE · Intro college organic15 items · answer key included This chirality worksheet gives students plenty of practice finding stereocentres and assigning R and S configuration with the Cahn–Ingold–Prelog (CIP) priority rules. The molecules are real ones students meet in biology and medicine: alanine, cysteine, lactic acid, glyceraldehyde, ibuprofen, carvone, thalidomide, ephedrine, penicillin G and both natural and meso tartaric acid. Each structure is drawn with wedges and dashes; students mark every chiral centre, rank the four groups and give the R/S label. Every answer in the key was verified with a computer CIP labeller, so this R and S configuration worksheet with answers is dependable for homework, revision and printable PDF quizzes. ## Customise Sheet title Subtitle School / teacher Student lines Name Class Date Answers None Answer key page Inline Text size S M L Structure size 100% Questions Find the stereocentres and assign R/S Alanine (natural L-alanine) Lactic acid (from muscle) Butan-2-ol Glyceraldehyde (D-glyceraldehyde) Bromochlorofluoromethane Ibuprofen (active enantiomer) Carvone (spearmint oil) Thalidomide Cysteine (natural L-cysteine) Ephedrine (+)-Tartaric acid (natural, from grapes) meso-Tartaric acid Penicillin G Check your understanding Which of these molecules are chiral: propan-2-ol, glycine, butan-2-ol… A pure sample of (S)-ibuprofen rotates plane-polarised light. What wo… Live A4 preview. “Download PDF” opens the print dialog: choose **Save as PDF**. Click a structure to open it in MolDraw. ## Chirality & R/S Configuration Worksheet Name Class Date ## Find the stereocentres and assign R/S Mark every stereocentre with an asterisk (*), number the four groups by CIP priority, and label each stereocentre R or S. 1. **Alanine (natural L-alanine)** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-88252ee793.svg) 1 stereocentre (C2, the α-carbon): **S**. Priorities: NH2 > COOH > CH3 > H. 2. **Lactic acid (from muscle)** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-c3382a00d8.svg) 1 stereocentre (C2): **R**. Priorities: OH > COOH > CH3 > H. 3. **Butan-2-ol** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-37ce944213.svg) 1 stereocentre (C2): **S**. Priorities: OH > CH2CH3 > CH3 > H. 4. **Glyceraldehyde (D-glyceraldehyde)** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-99a602b2fd.svg) 1 stereocentre (C2): **R**. Priorities: OH > CHO > CH2OH > H. D-Glyceraldehyde is (*R*). 5. **Bromochlorofluoromethane** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-8ca9c6d006.svg) 1 stereocentre (the only carbon): **R**. Priorities: Br > Cl > F > H. 6. **Ibuprofen (active enantiomer)** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-c3582dca7d.svg) 1 stereocentre (C2 of the propanoic acid, bearing CH3): **S**. Priorities: COOH > aryl > CH3 > H. (*S*)-ibuprofen is the active painkiller. 7. **Carvone (spearmint oil)** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-163387fb8a.svg) 1 stereocentre (ring C5, bearing the isopropenyl group): **R**. (*R*)-carvone smells of spearmint; its enantiomer (*S*)-carvone smells of caraway. 8. **Thalidomide** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-ca830c9912.svg) 1 stereocentre (the glutarimide CH bonded to N): **R**. Priorities: N(phthalimide) > C(=O)N > CH2 > H. (*R*)-thalidomide is the sedative; the two enantiomers interconvert in the body. 9. **Cysteine (natural L-cysteine)** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-b02752952e.svg) 1 stereocentre (α-carbon): **R**. Priorities: NH2 > CH2SH > COOH > H (S outranks O). L-Cysteine is *R*, unlike most L-amino acids, which are *S*. 10. **Ephedrine** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-1e4761c5d1.svg) 2 stereocentres: C1 (bearing OH and phenyl) is **R**; C2 (bearing NHCH3 and CH3) is **S**. (1*R*,2*S*)-ephedrine. 11. **(+)-Tartaric acid (natural, from grapes)** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-0ca5d98db3.svg) 2 stereocentres: C2 **R** and C3 **R** — (2*R*,3*R*)-tartaric acid. Chiral (no internal mirror plane). 12. **meso-Tartaric acid** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-3ecdc639f7.svg) 2 stereocentres: one **R** and one **S** — (2*R*,3*S*). The molecule has an internal mirror plane, so it is a *meso* compound and is achiral (optically inactive) despite having two stereocentres. 13. **Penicillin G** ![Structure for the question](https://www.moldraw.com/educational-materials/img/chirality-rs-worksheet/s-f368928f23.svg) 3 stereocentres: C2 (bearing COOH) **S**; C5 (ring-fusion CH next to S) **R**; C6 (bearing the amide NH) **R** — (2*S*,5*R*,6*R*). The C(CH3)2 carbon is not a stereocentre. ## Check your understanding Answer each question in the space provided. 14. Which of these molecules are chiral: propan-2-ol, glycine, butan-2-ol, 2-chloropropane, 2-chlorobutane? Only **butan-2-ol** and **2-chlorobutane**. In the others, the central carbon carries two identical groups (two CH3 groups, or two H atoms in glycine). 15. A pure sample of (*S*)-ibuprofen rotates plane-polarised light. What would you observe for a racemic mixture, and why? No rotation. A racemic mixture contains equal amounts of the *R* and *S* enantiomers, which rotate plane-polarised light by equal amounts in opposite directions, so the effects cancel. moldraw.com/educational-materials/chirality-rs-worksheet/ ## Answer key: Chirality & R/S Configuration Worksheet ## Find the stereocentres and assign R/S 1. 1 stereocentre (C2, the α-carbon): **S**. Priorities: NH2 > COOH > CH3 > H. 2. 1 stereocentre (C2): **R**. Priorities: OH > COOH > CH3 > H. 3. 1 stereocentre (C2): **S**. Priorities: OH > CH2CH3 > CH3 > H. 4. 1 stereocentre (C2): **R**. Priorities: OH > CHO > CH2OH > H. D-Glyceraldehyde is (*R*). 5. 1 stereocentre (the only carbon): **R**. Priorities: Br > Cl > F > H. 6. 1 stereocentre (C2 of the propanoic acid, bearing CH3): **S**. Priorities: COOH > aryl > CH3 > H. (*S*)-ibuprofen is the active painkiller. 7. 1 stereocentre (ring C5, bearing the isopropenyl group): **R**. (*R*)-carvone smells of spearmint; its enantiomer (*S*)-carvone smells of caraway. 8. 1 stereocentre (the glutarimide CH bonded to N): **R**. Priorities: N(phthalimide) > C(=O)N > CH2 > H. (*R*)-thalidomide is the sedative; the two enantiomers interconvert in the body. 9. 1 stereocentre (α-carbon): **R**. Priorities: NH2 > CH2SH > COOH > H (S outranks O). L-Cysteine is *R*, unlike most L-amino acids, which are *S*. 10. 2 stereocentres: C1 (bearing OH and phenyl) is **R**; C2 (bearing NHCH3 and CH3) is **S**. (1*R*,2*S*)-ephedrine. 11. 2 stereocentres: C2 **R** and C3 **R** — (2*R*,3*R*)-tartaric acid. Chiral (no internal mirror plane). 12. 2 stereocentres: one **R** and one **S** — (2*R*,3*S*). The molecule has an internal mirror plane, so it is a *meso* compound and is achiral (optically inactive) despite having two stereocentres. 13. 3 stereocentres: C2 (bearing COOH) **S**; C5 (ring-fusion CH next to S) **R**; C6 (bearing the amide NH) **R** — (2*S*,5*R*,6*R*). The C(CH3)2 carbon is not a stereocentre. ## Check your understanding 14. Only **butan-2-ol** and **2-chlorobutane**. In the others, the central carbon carries two identical groups (two CH3 groups, or two H atoms in glycine). 15. No rotation. A racemic mixture contains equal amounts of the *R* and *S* enantiomers, which rotate plane-polarised light by equal amounts in opposite directions, so the effects cancel. ## How to use this worksheet 1. Recap the CIP rules first: rank by atomic number at the first point of difference; double bonds count as duplicated atoms. 2. Remind students: if the lowest-priority group (usually H) points towards the viewer (wedge), the direction 1→2→3 gives the opposite label. 3. Ask students to write the priorities 1–4 next to each group before deciding R or S — this is where most marks are lost. 4. Cysteine (a9) and meso-tartaric acid (a12) are good discussion questions about why L ≠ S and why two stereocentres do not always make a molecule chiral. 5. Set the title, student lines and answer option on the left, then press **Download PDF** and choose “Save as PDF” (or print directly). Your choices are remembered on this device. **Draw and edit structures in MolDraw.** Make your own questions: draw any molecule, then export it as PNG or SVG for your worksheets. [Draw and edit structures in MolDraw](https://www.moldraw.com/) ## Frequently asked questions ### How do you assign R or S configuration? Rank the four groups on the stereocentre by the CIP rules (higher atomic number = higher priority). Orient the molecule so the lowest-priority group points away from you, then trace 1 → 2 → 3: clockwise is R, anticlockwise is S. If the lowest-priority group points towards you, reverse the answer. ### How do you identify a chiral centre (stereocentre)? Look for an sp3 carbon bonded to four different groups. CH2 and CH3 carbons, carbons in C=C or C=O, and carbons with two identical substituents (such as the C(CH3)2 in penicillin) are not stereocentres. ### What is a meso compound? A meso compound has two or more stereocentres but also an internal mirror plane, so it is superimposable on its mirror image and is achiral. meso-Tartaric acid (2R,3S) is the classic example. ### Is L the same as S for amino acids? Usually, but not always. Most natural L-amino acids are S, but L-cysteine is R because the CH2SH group outranks COOH (sulfur has a higher atomic number than oxygen). ### Are the R/S answers checked? Yes. Every R/S label in the answer key was checked with RDKit's implementation of the current CIP rules. 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