C4: Organic Synthesis and Spectroscopic Analysis

Year 1 / ASYear 2 / A-Level All Boards (AQA, Edexcel, OCR, WJEC, CCEA) AQA

¹H and ¹³C NMR spectroscopy, Infrared spectroscopy, High-resolution Mass Spectrometry, synthetic routes.

Exam Board:

📋 Key Definitions and Core Concepts

Chemical Shift (δ): Resonant frequency position relative to TMS standard at δ = 0 ppm in ppm.

Spin-Spin Splitting: (n+1) rule: proton signal split into n+1 peaks by n non-equivalent adjacent protons.

🔍 Key Principles & Specification Requirements

IR key absorptions: O-H alcohol (broad 3200-3600 cm⁻¹), O-H acid (very broad 2500-3300 cm⁻¹), C=O carbonyl (sharp 1680-1750 cm⁻¹).
¹³C NMR: number of distinct signals = number of unique carbon environments.
High-resolution MS: accurate m/z to 4 decimal places distinguishes compounds with same integer mass.

💡 Worked Example Question

Exam-Style Question

Question:

Identify C₃H₆O₂ showing IR 1715 cm⁻¹, broad 2500-3300 cm⁻¹, ¹H NMR triplet δ 1.1 (3H), quartet δ 2.4 (2H), singlet δ 11.5 (1H).

Model Solution & Mark Scheme:

1. IR: 1715 cm⁻¹ (C=O) + 2500-3300 cm⁻¹ (acid O-H) => carboxylic acid (-COOH).
2. ¹H NMR: δ 11.5 singlet is -COOH proton.
3. Triplet δ 1.1 (3H) and quartet δ 2.4 (2H) indicates ethyl group CH₃CH₂-.
Structure: Propanoic acid (CH₃CH₂COOH).

❓ Practice Questions & Mark Schemes

Q1: Why is TMS used as NMR standard?

Show Model Answer

Answer: Single sharp peak at δ = 0 ppm, inert, non-toxic, volatile (easily evaporated).

Q2: Describe the D₂O shake in ¹H NMR.

Show Model Answer

Answer: D₂O exchanges with labile -OH and -NH protons (R-OH + D₂O → R-OD + HOD), causing their signals to disappear from the spectrum.

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🎬 Video Resources

Organic Synthesis and Spectroscopic Analysis - Overview -- YouTube Search
Organic Synthesis and Spectroscopic Analysis - Exam Questions -- YouTube Search

📄 Past Papers & Exam Resources

AQA A-Level - Past Papers -- AQA
Edexcel A-Level - Past Papers -- Edexcel
OCR A-Level - Past Papers -- OCR

🔗 Further Reading & Resources

Physics & Maths Tutor -- Free notes, worksheets, and past paper questions by topic
Dr Frost Maths -- Free resources, slides, and interactive questions
BBC Bitesize -- BBC Bitesize revision resources

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