Answer
Interpretation of the ¹H-NMR Spectrum of Berberine
Overview
The ¹H-NMR spectrum of berberine provides detailed information about the types and environments of hydrogen atoms present in the molecule. This analysis includes identification of aromatic, methylene, methoxy, and methylenedioxy groups based on their chemical shifts.
Chemical Shift Assignments
| Chemical Shift (ppm) | Proton Type / Assigned Group |
|---|---|
| 8.0 – 8.5 | Aromatic protons (rings A, C, D) |
| 7.0 – 7.5 | Additional aromatic proton environments |
| 6.0 | Methylenedioxy group (–O–CH₂–O–) |
| 4.0 | Two methoxy groups (–OCH₃), singlets |
| 3.3 | Methylene protons near quaternary N⁺ |
| 1.0 – 2.0 | Trace impurities (non-structural) |
Structural Analysis of Berberine
Berberine consists of four fused rings labeled A, B, C, and D. Aromatic protons are located in rings A, C, and D. Ring B contains methylene and methine protons. The positively charged nitrogen (N⁺) deshields nearby protons, affecting their chemical shift. The two methoxy groups appear as distinct singlets around 4.0 ppm, and the methylenedioxy group appears at 6.0 ppm.
Impurity Assessment
Small peaks between 1.0 – 2.0 ppm are attributed to trace impurities and do not affect the main spectrum. All significant signals match the expected chemical shifts for berberine, confirming sample purity.
Conclusion
✅ The proton NMR spectrum aligns perfectly with the structure of berberine. All major functional groups are represented by their expected chemical shifts, and no unexpected peaks were observed. This confirms both the structural integrity and purity of the sample.