Drawing Possible Isomers of Organic Compounds

Learn how to draw structural, chain, position, and functional isomers of organic compounds with simple rules and examples by Inam Jazbi.

Isomerism is one of the most fascinating topics in organic chemistry. Different compounds can have the same molecular formula but entirely different structures and properties — these are called isomers.

In this detailed post from Learn Chemistry by Inam Jazbi, you’ll discover how to draw all possible isomers of organic compounds step-by-step, including chain, position, and functional isomers. Each concept is explained clearly with easy tricks, examples, and visual patterns — perfect for MDCAT, FSc, and O Level students who want to master organic chemistry.

🧪 MDCAT-style MCQs (Ready HTML) — Learn Chemistry by Inam Jazbi

This page contains ready-to-paste HTML sections for your Blogger posts: Acids, Bases & Salts MCQs, Isomerism MCQs, and Advanced Isomerism (Geometrical & Optical). All questions have four options and short explanations; answers are intentionally not marked so students can attempt them.

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💧 Acids, Bases & Salts — MCQs (4 options; answers not marked)

1. Which of the following is an Arrhenius acid?

A) NaOH B) NH₃ C) HCl D) K₂CO₃

Explanation: Arrhenius acids release H⁺ ions in water. For example, HCl → H⁺ + Cl⁻.

2. Which of the following acts as a Bronsted–Lowry base?

A) H₂SO₄ B) NH₃ C) HCl D) H₂O

Explanation: A Bronsted–Lowry base is a proton (H⁺) acceptor. NH₃ accepts H⁺ from water to form NH₄⁺.

3. Which of the following is a Lewis acid?

A) NH₃ B) BF₃ C) OH⁻ D) H₂O

Explanation: A Lewis acid accepts an electron pair. BF₃ can accept an electron pair from NH₃.

4. Which salt is formed when HCl reacts with NaOH?

A) KCl B) NaCl C) NH₄Cl D) Na₂SO₄

Explanation: HCl + NaOH → NaCl + H₂O. Neutralization produces a salt and water.

5. Which of the following pairs is a conjugate acid–base pair?

A) H₂SO₄ / SO₄²⁻ B) NH₄⁺ / NH₃ C) HCl / Cl₂ D) NaOH / H₂O

Explanation: A conjugate acid–base pair differs by one proton. NH₄⁺ donates H⁺ to form NH₃.

6. Which of the following is a basic salt?

A) NaCl B) CH₃COONa C) NH₄Cl D) KNO₃

Explanation: CH₃COONa is formed from a weak acid (CH₃COOH) and a strong base (NaOH), making its solution basic.

7. Which solution has a pH less than 7?

A) NaOH B) H₂SO₄ C) Na₂CO₃ D) KOH

Explanation: Acids have pH < 7. H₂SO₄ is a strong acid producing many H⁺ ions.

8. Which salt solution is acidic?

A) NH₄Cl B) Na₂CO₃ C) KCl D) NaCl

Explanation: NH₄Cl comes from a weak base (NH₃) and strong acid (HCl), so its aqueous solution is acidic.

9. Which of the following acids is diprotic?

A) HCl B) H₂SO₄ C) HNO₃ D) CH₃COOH

Explanation: Diprotic acids can donate two protons. H₂SO₄ → 2H⁺ + SO₄²⁻.

10. What is the product of neutralization between HNO₃ and KOH?

A) K₂SO₄ B) KNO₃ C) NH₄NO₃ D) NaNO₃

Explanation: HNO₃ + KOH → KNO₃ + H₂O. Acid + base → salt + water.

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🔹 Isomerism — MCQs (Stylish & Coloured)

Set font to Cambria in Blogger Compose view. Questions are highlighted in blue; explanations in green italic.

1. Compounds having the same molecular formula but different structures are called:

A) Isotopes B) Isomers C) Allotropes D) Homologues

Explanation: Isomers have the same molecular formula but differ in the arrangement of atoms, giving different structures and properties.

2. Which type of isomerism is shown by pentane, isopentane, and neopentane?

A) Chain isomerism B) Position isomerism C) Functional isomerism D) Metamerism

Explanation: These compounds differ in branching of the carbon chain, so they show chain isomerism.

3. Which of the following pairs shows position isomerism?

A) CH₃CH₂OH and CH₃OCH₃ B) C₂H₅Br and CH₃CH₂Br C) CH₃CH₂Cl and CH₂ClCH₃ D) CH₃OH and CH₃OCH₃

Explanation: In CH₃CH₂Cl and CH₂ClCH₃, the position of Cl changes on the same carbon chain.

4. Which of the following compounds are functional isomers?

A) Ethanol and dimethyl ether B) Propane and propene C) Butane and methylpropane D) Methanol and methanal

Explanation: Ethanol (C₂H₅OH) and dimethyl ether (CH₃OCH₃) are functional isomers (alcohol vs ether).

5. Which type of isomerism occurs due to different functional groups?

A) Chain B) Position C) Functional D) Optical

Explanation: Functional isomerism arises when compounds have the same molecular formula but different functional groups.

6. The number of possible isomers of butane (C₄H₁₀) is:

A) 2 B) 3 C) 4 D) 5

Explanation: Butane has two isomers — n-butane and isobutane (methylpropane).

7. Which of the following shows metamerism?

A) Ethers B) Alkanes C) Alkenes D) Alcohols

Explanation: Metamerism occurs in ethers (R–O–R') where different alkyl groups are attached to the same functional group.

8. Isomerism due to different spatial arrangements of atoms is called:

A) Structural isomerism B) Stereoisomerism C) Chain isomerism D) Position isomerism

Explanation: Stereoisomerism means same structural formula but different 3D arrangement of atoms in space.

9. Cis–trans isomerism is a type of:

A) Structural isomerism B) Geometrical isomerism C) Optical isomerism D) Chain isomerism

Explanation: Cis–trans is a form of geometrical isomerism found in alkenes due to restricted rotation around double bonds.

10. Butanoic acid (C₃H₇COOH) and methylpropanoic acid (CH₃CH(CH₃)COOH) show:

A) Chain isomerism B) Position isomerism C) Functional isomerism D) Tautomerism

Explanation: They differ in carbon chain arrangement, so this is chain isomerism.

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🔷 Advanced Isomerism — Geometrical & Optical (MCQs + Short Notes)

This section covers geometrical isomerism (cis/trans or E/Z) and optical isomerism (chirality, enantiomers, meso compounds) — include diagrams in your blog if possible for best clarity.

1. Geometrical (cis–trans) isomerism is possible when:

A) There is a double bond and each carbon has two different groups B) There is free rotation around the bond C) Molecule is symmetrical D) There is an sp hybridized carbon

Explanation: For cis–trans isomerism (or E/Z), rotation around the double bond is restricted and each carbon of the double bond must have two different substituents.

2. Which of the following pairs are geometric isomers?

A) 1,2-dichloroethane (both Cl on same carbon) B) 2-butene (cis and trans) C) Butane (single bond) D) Ethane

Explanation: 2-butene exists as cis-2-butene and trans-2-butene because of restricted rotation about the C=C bond and different groups on each carbon.

3. A carbon atom bonded to four different groups is called:

A) Planar carbon B) Chiral center (stereocentre) C) sp2 carbon D) Achiral carbon

Explanation: A carbon bonded to four different substituents is a stereocentre and gives rise to non-superimposable mirror images (enantiomers).

4. Enantiomers are:

A) Identical compounds B) Mirror-image, non-superimposable isomers C) Constitutional isomers D) Geometric isomers

Explanation: Enantiomers are stereoisomers that are non-superimposable mirror images and often have different optical rotation.

5. A molecule with two chiral centers that is superimposable on its mirror image is called:

A) Enantiomer B) Diastereomer C) Meso compound D) Structural isomer

Explanation: Meso compounds have internal plane of symmetry despite having chiral centres, making them achiral overall.

6. Optical activity is measured by:

A) Melting point B) Polarimeter (specific rotation) C) Boiling point D) pH meter

Explanation: A polarimeter measures the rotation of plane-polarized light by chiral compounds; specific rotation is a physical constant for enantiomers.

7. Which statement is true about enantiomers?

A) They have identical physical properties in achiral environments except for direction of optical rotation B) They are always identical in chemical behaviour in chiral environments C) They have different melting points by large amounts D) They are structural isomers

Explanation: Enantiomers have identical physical properties (bp, mp, refractive index) in achiral environments but rotate plane-polarized light in opposite directions and react differently in chiral environments.

8. Which of the following can show optical isomerism?

A) A molecule with no chiral centre B) Molecule with one chiral centre (non-symmetric) C) A meso compound D) A symmetrical molecule

Explanation: Molecules with one non-equivalent chiral centre (no internal symmetry) can show optical isomerism (enantiomers).

9. The relationship between enantiomers is analogous to:

A) Left and right hands B) Mirror images that are superimposable C) Isotopes D) Structural isomers

Explanation: Enantiomers are like left and right hands — mirror images but not superimposable.

10. How many stereoisomers are possible for a molecule with two non-equivalent chiral centres (no meso)?

A) 2 B) 3 C) 4 D) 8

Explanation: For n chiral centres, maximum stereoisomers = 2^n. With two non-equivalent chiral centres, 2^2 = 4 stereoisomers (2 enantiomeric pairs).

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✳️ How to use: Copy this HTML into Blogger > New Post > HTML view. Switch to Compose to fine-tune font size (Large for questions, Medium for explanations) and to add diagrams for advanced isomer examples.

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