Chemsheets Organic Synthesis Problems | Answers

Problem (Chemsheets A2 1080 style):
Starting from benzene, prepare 4-aminobenzoic acid in 4 steps.

Answer:

Step 1: Benzene → Methylbenzene (toluene)

Step 2: Methylbenzene → 4-methylbenzoic acid

Step 3: 4-methylbenzoic acid → 4-nitrobenzoic acid

Step 4: Nitro group → amino group

But target was 4-aminobenzoic acid? This shows why synthesis planning must consider directing groups. A correct 4-aminobenzoic acid route:
Benzene –(HNO₃/H₂SO₄)→ Nitrobenzene –(Sn/HCl)→ Phenylamine –(CH₃Cl, AlCl₃?) No – amino group reacts with AlCl₃. So protect first? Too complex. Chemsheets often expects:
Benzene → Chlorobenzene → 4-nitrochlorobenzene → 4-nitrophenol → 4-aminophenol – not right for 4-aminobenzoic acid.
The actual simple route:
Benzene –(CH₃Cl, AlCl₃)→ Methylbenzene –(KMnO₄)→ Benzoic acid –(HNO₃/H₂SO₄)→ 3-nitrobenzoic acid –(Sn/HCl)→ 3-aminobenzoic acid.
To get 4-aminobenzoic acid, you need to start with aniline and protect –NH₂, or start with benzoic acid and nitrate at 4-position, which is impossible due to meta direction. So Chemsheets sometimes uses “wrong” syntheses to test understanding of limitations. Chemsheets Organic Synthesis Problems Answers

Thus the correct Chemsheets answer for 4-aminobenzoic acid from benzene is:

Chemsheets.co.uk has become a staple in UK chemistry departments for a reason. Their synthesis worksheets are not just lists of reactions; they are puzzles.

1. Complexity and Variety Chemsheets problems often involve multi-step syntheses. You aren't just converting an alkene to an alcohol; you might be converting an alkene to a polymer precursor in four steps, requiring purification and isomer consideration.

2. Focus on Conditions One of the most common ways students lose marks is omitting reaction conditions.

3. Ambiguity Resolution Many synthesis problems provide limited information, forcing students to deduce the structure of 'Compound A' based on the properties of 'Compound B'. This mirrors the analytical style of actual examination papers (like OCR or AQA).

If you are currently studying A-Level Chemistry (or an equivalent introductory university course), you have likely heard the two words that strike both fear and excitement into the hearts of students: Organic Synthesis. Problem (Chemsheets A2 1080 style): Starting from benzene

Linking a benzene ring to a chiral amine via a 4-step pathway requires a specific kind of logical thinking. One of the most popular resources for drilling this skill is the Chemsheets series of organic synthesis problems.

But let’s be honest: Working through these sheets is tough. Getting stuck is normal. Simply looking up a PDF of "answers" won't teach you why a reaction works.

Here is how to use Chemsheets Organic Synthesis problems and their answers effectively—without cheating yourself out of the learning.

Problem: Synthesise 2-methylbutan-2-ol from ethanol (max 3 steps).

Answer:

Step 1: Ethanol → Ethanal (oxidation, distil)
Step 2: Ethanal + CH₃MgBr (Grignard from bromomethane + Mg in dry ether) → after acid work-up, gives propan-2-ol (but that’s not target).
Correct: Need to make 2-methylbutan-2-ol: (CH₃)₃C–CH(OH)–CH₃? Wait, structure: (CH₃)₂C(OH)CH₂CH₃.
From ethanol: Step 2: Methylbenzene → 4-methylbenzoic acid

Better: Known answer:

Simpler:
Ethanol –[O]→ Ethanal –[O]→ Ethanoic acid –(SOCl₂)→ Ethanoyl chloride –(2 CH₃MgBr)→ 2-methylbutan-2-ol. That’s 4 steps.

Organic synthesis is the art of constructing specific organic molecules from simpler starting materials. In A-Level exams, this usually manifests in two ways:

The difficulty lies in the sheer volume of knowledge required. Students must recall:

Chemsheets excels because it creates problems that are specifically designed to trip students up on these precise details. It forces you to distinguish between what works and what works best.