# Further Organic Chemistry (IB HL)
At HL, organic chemistry extends to reaction pathways connecting functional groups, and the use of spectroscopic techniques (MS, IR, ¹H NMR) to identify unknown compounds.
1. Reaction Pathways
Key Conversions
- Alkene → alcohol: addition of H₂O (acid catalyst)
- Alkene → halogenoalkane: addition of HX
- Halogenoalkane → alcohol: NaOH(aq), reflux
- Halogenoalkane → amine: excess NH₃, heat
- Halogenoalkane → nitrile: KCN (extends chain by 1 C)
- Alcohol → aldehyde/acid: oxidation with Cr₂O₇²⁻/H⁺
- Alcohol → alkene: dehydration
- Nitrile → carboxylic acid: hydrolysis (dilute acid, reflux)
2. Mass Spectrometry
- peak: molecular mass
- Fragmentation: characteristic peaks identify structural features
- Base peak: most abundant fragment (100%)
3. IR Spectroscopy
Key absorptions:
- O−H (alcohol): 3200–3550 cm⁻¹ (broad)
- O−H (acid): 2500–3300 cm⁻¹ (very broad)
- C=O: 1700–1750 cm⁻¹ (strong, sharp)
- N−H: 3300–3500 cm⁻¹
- C−O: 1000–1300 cm⁻¹
Fingerprint region (<1500 cm⁻¹) is unique to each molecule.
4. ¹H NMR Spectroscopy
- Number of peaks = different H environments
- Chemical shift (δ) = type of environment
- Integration = relative number of H
- Splitting: n+1 rule (n = adjacent equivalent H)
| Environment | δ (ppm) |
|---|---|
| RCH₃ | 0.9 |
| RCH₂R | 1.3 |
| C=C−H | 4.5–6.0 |
| R−CHO | 9–10 |
| R−COOH | 10–12 |
| ArH | 6.5–8.0 |
D₂O shake: removes O−H and N−H peaks.
5. Combined Analysis Strategy
- MS: determine molecular formula from
- IR: identify functional groups
- NMR: determine H environments, symmetry, and connectivity
- Propose structure consistent with all data
6. Practice Questions
- A compound has , shows C=O absorption in IR, and ¹H NMR shows a triplet and quartet. Identify it.
- Design a two-step synthesis of propan-1-ol from 1-bromopropane.
- A compound C₃H₆O shows a peak at δ 9.8 in ¹H NMR. What functional group is present?
- Explain how you would convert ethanol to ethylamine.
- Use the IB Data Booklet to identify absorptions at 1720 cm⁻¹ and 2900 cm⁻¹.
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Summary
- Reaction pathways connect all functional groups through specific reagents/conditions
- MS: molecular mass and fragmentation
- IR: functional group identification
- ¹H NMR: hydrogen environments, splitting, integration
- Combine all techniques to deduce unknown structures