Interpretation of ¹H NMR Spectrum of Berberine

1. Structure & Chemical Features

Molecular Formula: C₂₀H₁₈NO₄⁺
Core: Tetracyclic isoquinoline alkaloid
Features: Aromatic rings, methoxy groups, methylenedioxy bridge, quaternary nitrogen

2. Expected ¹H NMR Regions

Region	δ (ppm)	Assignment	Type	Integration
Aromatic	7.0 – 8.5	H-1, H-4, H-5, H-7, H-8	Multiplet	1H each
Methoxy (OCH₃)	3.9 – 4.1	Positions 2, 3, 9, 10	Singlet	3H each
CH₂–N⁺	5.2 – 5.4	Bridgehead CH₂	Singlet	2H
Aliphatic CH₂	2.5 – 3.0	C-ring CH₂s	Multiplet	2H or 4H

3. Peak Assignments

Aromatic Region (7.0–8.5 ppm)

H-8 → 8.25 ppm (Doublet/Multiplet)
H-1 → 7.95 ppm (Multiplet)
H-5, H-7 → 7.50–7.60 ppm (Doublets)
H-4 → 7.0–7.2 ppm (Triplet/Multiplet)

Methoxy Groups (~4.0 ppm)

OCH₃-2 → 4.00 ppm
OCH₃-3 → 3.95 ppm
OCH₃-9 → 3.92 ppm
OCH₃-10 → 3.89 ppm

CH₂–N⁺ Region (~5.3 ppm)

Singlet at 5.30 ppm → Benzylic CH₂ attached to quaternary nitrogen

Aliphatic CH₂ Region (2.6–2.9 ppm)

Broad multiplet → CH₂ groups in ring C (4H total approx.)

Note: Minor variations in chemical shift are expected due to the use of MeOD-d₄ solvent and sample concentration.

Conclusion

The NMR spectrum confirms the presence of berberine with distinct and expected signals for aromatic, methoxy, bridgehead CH₂, and aliphatic protons. Each peak corresponds to specific protons in the structure. This validates the compound’s identity through spectral data.

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