MolDraw › Educational materials › Structural Isomers & Stereoisomers Worksheet

Structural Isomers & Stereoisomers Worksheet

Organic chemistryGrades 11–12 · A-level / IB · AP Chemistry · CBSE/JEE · Intro college organic10 items · answer key included

This isomers worksheet asks students to draw every structural isomer of a molecular formula and then think about stereoisomers. Part A covers the classic exam formulas: the 3 isomers of C5H12, the 6 isomers of C4H8 (including cyclic and cis/trans forms), the 7 alcohols and ethers of C4H10O and the carbonyl, alcohol, ether and ring isomers of C3H6O. Part B practises cis/trans (E/Z) and optical isomerism, including meso compounds. The answer key shows every structure with its IUPAC name, and each count was checked by computer enumeration, so this structural isomers worksheet with answers is reliable for homework, revision or a printable PDF test.

Live A4 preview. “Download PDF” opens the print dialog: choose Save as PDF. Click a structure to open it in MolDraw.

Structural Isomers & Stereoisomers Worksheet

Name Class Date

Part A — Draw all the structural isomers

Draw and name every structural (constitutional) isomer of each formula. Then note any that also show stereoisomerism.

1.
Draw and name all the structural isomers of C5H12.
3 isomers: pentane; 2-methylbutane; 2,2-dimethylpropane.Answer structureAnswer structureAnswer structure
2.
Draw and name all the isomers of C4H8, including cyclic compounds and cis/trans isomers.
6 isomers (5 structural + 1 extra stereoisomer): but-1-ene; (Z)-but-2-ene (cis); (E)-but-2-ene (trans); 2-methylpropene; cyclobutane; methylcyclopropane.Answer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structure
3.
Draw and name all the structural isomers of C4H10O. Classify each as an alcohol (primary, secondary or tertiary) or an ether.
7 isomers. Alcohols: butan-1-ol (1°); butan-2-ol (2°, chiral — exists as R and S); 2-methylpropan-1-ol (1°); 2-methylpropan-2-ol (3°). Ethers: 1-methoxypropane; 2-methoxypropane; ethoxyethane (diethyl ether).Answer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structure
4.
C3H6O: (a) draw and name the two carbonyl compounds; (b) draw and name as many other structural isomers as you can (alcohols, ethers and rings).
(a) propanal (aldehyde) and propanone (acetone, ketone). (b) prop-2-en-1-ol (allyl alcohol); methoxyethene (methyl vinyl ether); cyclopropanol; oxetane; 2-methyloxirane (propylene oxide, chiral); plus the unstable enols prop-1-en-1-ol (E/Z) and prop-1-en-2-ol. 9 structural isomers in total (7 if enols are excluded).Answer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structure
5.
Draw and name all the structural isomers of C3H8O. Which one is an ether?
3 isomers: propan-1-ol; propan-2-ol; methoxyethane (ethyl methyl ether — the ether). The two alcohols are position isomers; the ether is a functional group isomer of them.Answer structureAnswer structureAnswer structure

Part B — Stereoisomers

Answer each question. Use wedges and dashes where you need to show 3-D arrangement.

6.
But-2-ene shows cis/trans (E/Z) isomerism but but-1-ene does not. Draw both isomers of but-2-ene and explain the difference.
Structure for the question
Restricted rotation about C=C plus two different groups on each alkene carbon is needed. In but-2-ene each carbon carries H and CH3, giving (Z)-but-2-ene (cis, CH3 groups same side) and (E)-but-2-ene (trans). In but-1-ene, C1 carries two H atoms, so no geometric isomers exist.Answer structureAnswer structure
7.
Mark the chiral centre in butan-2-ol and draw its two enantiomers as wedge/dash structures.
Structure for the question
C2 (bonded to H, OH, CH3 and CH2CH3) is the chiral centre. The two non-superimposable mirror images are (R)-butan-2-ol and (S)-butan-2-ol.Answer structureAnswer structure
8.
2,3-Dibromobutane has two stereocentres. How many stereoisomers does it have? Explain why it is fewer than 22 = 4.
Structure for the question
3 stereoisomers: (2R,3R) and (2S,3S) — a pair of enantiomers — and the meso form (2R,3S). The meso compound has an internal mirror plane, so it is identical to its mirror image (2S,3R) and is achiral.Answer structureAnswer structureAnswer structure
9.
Draw the stereoisomers of 1,2-dimethylcyclopropane. Which ones are chiral?
Structure for the question
3 stereoisomers: cis-1,2-dimethylcyclopropane (meso, achiral — has a mirror plane) and the two enantiomers of trans-1,2-dimethylcyclopropane, (1R,2R) and (1S,2S), which are chiral.Answer structureAnswer structureAnswer structure
10.
Which of these show cis/trans isomerism: (a) pent-1-ene, (b) pent-2-ene, (c) 2-methylbut-2-ene, (d) 1,2-dichloroethene?
(b) pent-2-ene and (d) 1,2-dichloroethene. Pent-1-ene has two H atoms on C1, and 2-methylbut-2-ene has two CH3 groups on C2, so neither can form geometric isomers.

moldraw.com/educational-materials/isomers-worksheet/

Answer key: Structural Isomers & Stereoisomers Worksheet

Part A — Draw all the structural isomers

1.
3 isomers: pentane; 2-methylbutane; 2,2-dimethylpropane.Answer structureAnswer structureAnswer structure
2.
6 isomers (5 structural + 1 extra stereoisomer): but-1-ene; (Z)-but-2-ene (cis); (E)-but-2-ene (trans); 2-methylpropene; cyclobutane; methylcyclopropane.Answer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structure
3.
7 isomers. Alcohols: butan-1-ol (1°); butan-2-ol (2°, chiral — exists as R and S); 2-methylpropan-1-ol (1°); 2-methylpropan-2-ol (3°). Ethers: 1-methoxypropane; 2-methoxypropane; ethoxyethane (diethyl ether).Answer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structure
4.
(a) propanal (aldehyde) and propanone (acetone, ketone). (b) prop-2-en-1-ol (allyl alcohol); methoxyethene (methyl vinyl ether); cyclopropanol; oxetane; 2-methyloxirane (propylene oxide, chiral); plus the unstable enols prop-1-en-1-ol (E/Z) and prop-1-en-2-ol. 9 structural isomers in total (7 if enols are excluded).Answer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structureAnswer structure
5.
3 isomers: propan-1-ol; propan-2-ol; methoxyethane (ethyl methyl ether — the ether). The two alcohols are position isomers; the ether is a functional group isomer of them.Answer structureAnswer structureAnswer structure

Part B — Stereoisomers

6.
Restricted rotation about C=C plus two different groups on each alkene carbon is needed. In but-2-ene each carbon carries H and CH3, giving (Z)-but-2-ene (cis, CH3 groups same side) and (E)-but-2-ene (trans). In but-1-ene, C1 carries two H atoms, so no geometric isomers exist.Answer structureAnswer structure
7.
C2 (bonded to H, OH, CH3 and CH2CH3) is the chiral centre. The two non-superimposable mirror images are (R)-butan-2-ol and (S)-butan-2-ol.Answer structureAnswer structure
8.
3 stereoisomers: (2R,3R) and (2S,3S) — a pair of enantiomers — and the meso form (2R,3S). The meso compound has an internal mirror plane, so it is identical to its mirror image (2S,3R) and is achiral.Answer structureAnswer structureAnswer structure
9.
3 stereoisomers: cis-1,2-dimethylcyclopropane (meso, achiral — has a mirror plane) and the two enantiomers of trans-1,2-dimethylcyclopropane, (1R,2R) and (1S,2S), which are chiral.Answer structureAnswer structureAnswer structure
10.
(b) pent-2-ene and (d) 1,2-dichloroethene. Pent-1-ene has two H atoms on C1, and 2-methylbut-2-ene has two CH3 groups on C2, so neither can form geometric isomers.

How to use this worksheet

  1. Encourage a systematic approach: longest chain first, then shorten the chain by one carbon at a time and move the branch or functional group.
  2. Students should name each isomer — two drawings with the same name are the same compound, which is the most common mistake.
  3. Clarify whether a question wants constitutional (structural) isomers only or stereoisomers too; the answer key gives both counts.
  4. Build the isomers in MolDraw and compare the generated names to spot duplicates.
  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

Frequently asked questions

How many isomers does C5H12 have?

C5H12 has three structural isomers: pentane, 2-methylbutane (isopentane) and 2,2-dimethylpropane (neopentane). None of them has stereoisomers.

How many isomers does C4H10O have?

C4H10O has 7 structural isomers: 4 alcohols (butan-1-ol, butan-2-ol, 2-methylpropan-1-ol, 2-methylpropan-2-ol) and 3 ethers (methoxypropane, 2-methoxypropane, ethoxyethane). Counting the two enantiomers of butan-2-ol gives 8 isomers in total.

How many isomers does C4H8 have?

C4H8 has 5 structural isomers (but-1-ene, but-2-ene, 2-methylpropene, cyclobutane and methylcyclopropane). But-2-ene exists as cis (Z) and trans (E) forms, so there are 6 isomers including stereoisomers.

What is the difference between structural isomers and stereoisomers?

Structural (constitutional) isomers have the same molecular formula but atoms joined in a different order. Stereoisomers have the same connectivity but a different 3-D arrangement, e.g. cis/trans isomers and enantiomers.

Are the answers included?

Yes. The answer key draws and names every isomer and explains each stereoisomer question. Download it as a free PDF with or without answers.

Related worksheets

Chirality & R/S Configuration WorksheetGrades 11–12 · A-level / IB · AP Chemistry · CBSE/JEE · Intro college organicIUPAC Naming WorksheetGrades 11–12 · A-level / IB · AP Chemistry · CBSE/JEE · Intro college organicFunctional Groups Identification WorksheetGrades 11–12 · A-level / IB · AP Chemistry · CBSE/JEE · Intro college organicCurved Arrow Mechanism WorksheetGrades 11–12 · A-level · AP / IB · CBSE/JEE · first-year universityPredict the Product Worksheet: Organic ReactionsGrades 11–12 · A-level · AP / IB · CBSE/JEE · first-year universityAll educational materialsWorksheets, lab activities, printables