Area of Study 2: How are organic compounds analysed and used?

You will be able to:

• Identify functional groups using qualitative chemical tests

• Determine purity using melting point and distillation

• Use redox titrations to quantify substances (e.g., Vitamin C)

• Interpret MS, IR, ¹H-NMR, ¹³C-NMR and chromatography data

• Deduce the structure of unknown organic compounds

• Explain how medicines interact with enzymes

• Analyse extraction and purification of natural medicines

1️⃣ Laboratory Analysis of Organic Compounds

Melting Point & Distillation

Used to determine purity:

• Pure substances have sharp melting points

• Impure substances melt over a wider range

• Distillation allows separation based on boiling point differences

Degree of Unsaturation – Iodine Value

• The more C=C bonds in a fat/oil, the more iodine it absorbs

• Used to compare oils (e.g., olive oil vs coconut oil)

Quantitative Redox Analysis

Students use redox titrations to measure:

• Vitamin C content

• Aldehyde/ketone concentrations

• Purity of consumer products

2️⃣ Instrumental Analysis Techniques

Instrumental techniques provide fast, accurate identification of organic compounds.

Mass Spectrometry (MS)

Used to determine:

• Molecular ion peak (M⁺) → molecular mass

• Fragmentation → structural pieces

Infrared Spectroscopy (IR)

Identifies bond types via absorption peaks:

• O–H (broad peak around 3200–3600 cm⁻¹)

• C=O (sharp peak around 1650–1800 cm⁻¹)

• C–H stretches

¹³C-NMR Spectroscopy

Shows:

• Number of different carbon environments

• Their chemical shift values

Great for identifying:

• Carbonyl groups

• Aromatic rings

• Quaternary carbons

¹H-NMR Spectroscopy

Provides:

• Chemical shifts

• Integration (number of hydrogens)

• Splitting patterns (n+1 rule)

Chromatography (HPLC)

Used to:

• Separate mixtures

• Identify chemicals via retention time

• Determine concentration using calibration curve

3️⃣ Medicinal Chemistry

Students explore how medicine molecules interact with biological systems.

Chirality

• Molecules with a carbon bonded to four different groups

• Enantiomers can behave differently in the body

• Only one may be useful or safe

Enzymes as Catalysts

• Proteins that speed up reactions in the body

• Have active sites shaped for specific substrates

Competitive inhibitors

• Molecules (medicines) that mimic a substrate

• Bind to the active site, preventing normal enzyme action

• Basis for many drugs: pain relief, antivirals, anticancer medicines

Conceptual Questions

1. How does IR spectroscopy help identify organic compounds?

2. Why is the molecular ion peak important in MS?

3. Explain why enantiomers can behave differently in the body.

4. Why does Vitamin C require a redox titration, not an acid–base titration?

Calculation Questions

6. A mass spectrum shows M⁺ at m/z = 88. What is the likely molecular mass?

7. An IR spectrum shows a sharp peak at ~1710 cm⁻¹. What functional group is present?

8. A ¹H-NMR spectrum shows a triplet and a quartet. Deduce a possible structure.

• Mixing up aldehyde and ketone IR peaks

• Forgetting to use integration in ¹H-NMR

• Mislabeling splitting patterns

• Assuming chromatography identifies structure (it doesn’t — identifies & quantifies)

• Using melting point data incorrectly without comparing to known benchmarks

• Memorise key IR absorption ranges

• Start every analysis problem with MS → IR → ¹H-NMR → ¹³C-NMR

• Practise identifying splitting patterns using n+1

• Draw structures as you interpret spectra

• For Vitamin C titration questions, always include accuracy, precision & repeatability