Organic synthesis: designing synthetic routes, identifying organic compounds

1️⃣ Key Concepts

Think of a synthetic route like a treasure map. Each step is a clue that brings you closer to the final treasure – the target molecule.

• Functional Groups are the “characters” in your story. Knowing their reactivity helps you choose the right “plot twists.”
• Retrosynthesis is the art of working backwards from the target to simpler starting materials.
• Yield & Selectivity are the “score” of your adventure – higher yield = more treasure, higher selectivity = fewer side‑quests.

2️⃣ Stepwise Synthesis Example

Let’s build aspirin (acetyl‑salicylic acid) from salicylic acid and acetic anhydride:

1. React salicylic acid with acetic anhydride in the presence of a catalyst (e.g., H₂SO₄).
2. Acetylation replaces the hydroxyl group with an acetyl group.
3. Work‑up: neutralise, extract, and recrystallise.

Reaction scheme:

3️⃣ Functional Group Identification

Use the “molecular fingerprint” approach:

• Alkanes – saturated C–C single bonds. Example: CH₃CH₂CH₃ (propane).
• Alkenes – C=C double bonds. Example: CH₂=CHCH₃ (propene).
• Alkynes – C≡C triple bonds. Example: CH≡CCH₃ (propyne).
• Aldehydes – R–CHO. Example: CH₃CHO (acetaldehyde).
• Ketones – R–CO–R. Example: CH₃COCH₃ (acetone).
• Carboxylic Acids – R–COOH. Example: CH₃COOH (acetic acid).
• Ethers – R–O–R. Example: CH₃OCH₃ (dimethyl ether).
• Esters – R–COO–R. Example: CH₃COOCH₃ (methyl acetate).

🔍 Tip: Look for the characteristic functional‑group peaks in IR or the splitting pattern in NMR.

4️⃣ Exam Tips & Tricks 📝

• Sketch the skeleton first. Draw the carbon backbone before adding heteroatoms.
• Work backwards. Start from the target and identify the most straightforward disconnections.
• Check for symmetry. Symmetrical molecules often simplify the synthesis.
• Remember the “rule of thumb”: “More functional groups = more steps.”
• Practice time management. Allocate 5 min for planning, 10 min for drawing, 5 min for checking.

💡 Remember: A clear, logical route is worth more than a clever but messy one.