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Where complex chemistry ideas turn into clear, colourful, and student-friendly concepts for every learner aiming high in MDCAT, ECAT, and Board exams.
Drawing organic molecules may look confusing at first, but the structure of every compound follows a simple set of universal rules. Once you understand how carbon behaves, how bonds are arranged, and how 3D shapes are shown on paper, organic chemistry becomes far easier to read and create.
This guide brings all essential rules together in a bright, exam-smart format to help you master organic structures like a pro.
🌟🔥 Rules for Drawing Organic Molecules | Complete Guide for MDCAT & ECAT 🔥🌟
1. C always has four bonds. This may consist of:
(i) 4 single
(ii) 1 double and 2 single
(iii) 1 triple and 1 single
(iv) 2 double
Carbon being tetravalent, tends to form four bonds. If you look at a variety of structures including carbon, you can see that nearly always each carbon atom has four bonding pairs of electrons, each represented as a line, surrounding it.
If a carbon has other electron arrangements in its valence shell (in other words, if it does not fulfill the octet rule), it will have a formal charge or exist as a radical:
2. H always has one bond.
3. O always has two bonds. This may consist of:
(i) 2 single
(ii) 1 double
For oxygen, you will see an oxygen atom bonding in three ways, all of which fulfill the octet rule.
In most cases an oxygen atom has two bonds and two lone pairs, as in does in water. In this arrangement it will have a formal charge of zero. If it has one bond and three lone pairs, as in hydroxide ion, it will have a formal charge of -1. If it has three bonds and one lone pair it will have a formal charge of +1.
4. X always has one bond. X = F, Cl, Br or I
5. N always has three bonds. This may consist of:
(i) 3 single
(ii) 1 single and 1 double
(iii) 1 triple
Nitrogen has two major bonding patterns, both of which fulfill the octet rule:
If a nitrogen has three bonds and a lone pair, it has a formal charge of zero. If it has four bonds (and no lone pair), it has a formal charge of +1. In a fairly uncommon bonding pattern, negatively charged nitrogen has two bonds and two lone pairs.
6. S may have 2, 4 or 6 bonds, but for this course it has 2 bonds.
🌟 Rules for Drawing Organic Molecules | Summary for MDCAT & ECAT 🌟
Organic structures are like coded maps: once you know the rules, you can draw even the toughest molecules with confidence. Here’s your bright, bite-sized guide:
🟦 1. Carbon Forms Four Bonds
Every carbon must complete 4 bonds through single, double or triple bonding.
✔ CH₄
✔ CH₃–CH₃
✔ C=O
✔ C≡N
🟩 2. Hydrogen Forms Only One Bond
Hydrogen never exceeds one single bond.
✔ H–C
✔ H–O
🟨 3. Use Bond-Line (Skeletal) Form Correctly
• Ends and corners = carbon atoms
• No need to write C or H on carbons
• H atoms are shown only when attached to heteroatoms
🟪 4. Show Lone Pairs on Heteroatoms (Optional but Useful)
O, N, S, X often carry lone pairs.
They help predict:
• Polarity
• Reactivity
• Hydrogen bonding
🟥 5. Respect Valency of Atoms
• Oxygen forms 2 bonds
• Nitrogen forms 3 (plus lone pair)
• Halogens form 1
• Sulfur often 2 or 6
🟧 6. Use Wedge–Dash Notation for 3D Structures
• Solid wedge (▲) → coming out
• Dashed wedge (▿) → going behind
• Straight line (–) → in plane
Essential for stereochemistry.
🟫 7. Draw Double/Triple Bonds Accurately
• Double bond = two parallel lines (=)
• Triple bond = three lines (≡)
• Maintain correct bond angles
🔷 8. Show Functional Groups Clearly
Always display:
• –OH
• –COOH
• –NH₂
• –CHO
• –C≡N
Functional groups decide naming + reactions.
🔶 9. Avoid Violating Octet Rule (Except in Exceptions)
Normal atoms follow:
• C → 8 electrons
• N → 8
• O → 8
Exceptions: B, P, S, radicals
🟣 10. Charge Placement Must Be Shown
Mark charges clearly:
• –OH₂⁺
• NH₄⁺
• CH₃O⁻
Charges help determine mechanism pathways.
🌟 Rules for Drawing Organic Molecules | Advanced MCQ Quiz 🌟
1️⃣ Carbon in organic molecules must always complete:
🟥 2 bonds
🟦 3 bonds
🟩 4 bonds
🟨 5 bonds
2️⃣ Hydrogen forms:
🟥 2 bonds
🟦 Only 1 bond
🟩 3 bonds
🟨 Variable bonds
3️⃣ In skeletal (bond-line) structures, the ends and corners represent:
🟥 Hydrogen atoms
🟦 Carbon atoms
🟩 Lone pairs
🟨 Charges only
4️⃣ Lone pairs must be shown when drawing:
🟥 Carbon atoms
🟦 Hydrogen atoms
🟩 Heteroatoms
🟨 Alkyl groups
5️⃣ A solid wedge (▲) represents:
🟥 A bond going behind
🟦 A bond in the plane
🟩 A bond coming out
🟨 A broken bond
6️⃣ A dashed wedge (▿) indicates:
🟥 Bond coming out
🟦 Bond going behind
🟩 Bond in plane
🟨 A double bond
7️⃣ A triple bond is drawn as:
🟥 One line
🟦 Two lines
🟩 Three lines
🟨 A dotted line
8️⃣ Oxygen usually forms:
🟥 1 bond
🟦 2 bonds
🟩 3 bonds
🟨 4 bonds
9️⃣ Nitrogen typically forms:
🟥 2 bonds
🟦 3 bonds
🟩 4 bonds
🟨 1 bond
🔟 Halogens usually form:
🟥 1 bond
🟦 2 bonds
🟩 3 bonds
🟨 4 bonds
1️⃣1️⃣ In bond-line formulas, hydrogens on carbon are:
🟥 Always shown
🟦 Never shown
🟩 Shown only when needed
🟨 Shown only for aromatic rings
1️⃣2️⃣ The octet rule is usually followed by:
🟥 C, N, O
🟦 H, C, He
🟩 Metals
🟨 Radicals only
1️⃣3️⃣ The symbol for a bond in plane of paper:
🟥 Solid wedge
🟦 Dashed wedge
🟩 Straight line
🟨 Curved arrow
1️⃣4️⃣ Formal charges must be shown when:
🟥 They affect reactivity
🟦 They look nice
🟩 They are large
🟨 Only in aromatic compounds
1️⃣5️⃣ A carbon with a positive charge (carbocation) has:
🟥 4 bonds
🟦 3 bonds
🟩 2 bonds
🟨 1 bond
1️⃣6️⃣ In resonance structures, what must remain unchanged?
🟥 Atom positions
🟦 Bond positions
🟩 Lone pairs
🟨 Charge placement
1️⃣7️⃣ Aromatic rings are drawn as:
🟥 Zig-zag chains
🟦 Hexagons
🟩 Pentagons
🟨 Squares
1️⃣8️⃣ A carbon–carbon double bond requires:
🟥 Free rotation
🟦 Restricted rotation
🟩 No electrons
🟨 Lone pairs only
1️⃣9️⃣ Skeletal formulas omit:
🟥 Carbon atoms
🟦 Hydrogen attached to heteroatoms
🟩 Bonds
🟨 Double bonds
2️⃣0️⃣ A tetrahedral carbon has bond angles close to:
🟥 90°
🟦 109.5°
🟩 120°
🟨 180°
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