Answer
¹H NMR Spectrum Analysis of Berberine
🔬 Step 1: Introduction
Berberine is a naturally occurring alkaloid featuring a typical isoquinoline structure. Its ¹H NMR spectrum provides critical information for identifying the presence of key hydrogen atoms. The analysis is performed in MeOD-d₄ solvent, and signals are assigned by comparing with known chemical shift values and structural patterns.
🎯 Step 2: Key Regions and Assignments
| Region (ppm) | Assignment | Nature of Signal |
|---|---|---|
| ~8.5 | H-8 (iminium proton) | Singlet – highly deshielded due to positive nitrogen |
| ~7.0 – 8.0 | H-11, H-12, H-13 (aromatic protons) | Multiplets and singlets – protons on ring D |
| ~6.0 – 6.5 | H-2 and H-3 (methylenedioxy bridge) | Two distinct peaks |
| ~4.5 | H-6 (methylene near quaternary nitrogen) | Multiplet |
| ~3.9 – 4.0 | Methoxy protons at C-9 and C-10 | Two sharp singlets |
| ~3.3 | Residual MeOD solvent peak | Singlet |
| ~2.5 – 3.0 | H-1, H-4, H-5 (benzylic/allylic CH₂) | Complex multiplets |
✅ Final Conclusion
The ¹H NMR spectrum shows excellent agreement with the expected features of berberine:
- Deshielded iminium proton at ~8.5 ppm
- Aromatic multiplets and singlets matching isoquinoline skeleton
- Distinct methylenedioxy bridge peaks in the 6–6.5 ppm range
- Sharp methoxy singlets in the ~4 ppm region
Note: For structural confirmation and connectivity, 2D NMR techniques such as COSY and HSQC are recommended.