Alkaloids are naturally occurring nitrogen-containing organic compounds, mainly obtained from plants, which usually possess basic character and show physiological activity.
Examples: Morphine, Quinine, Papaverine, Cinchonine.
General Definition
Basic, nitrogen-containing compounds isolated from plants.
Konig's Definition
Naturally occurring organic bases containing a pyridine ring.
Ladenburg's Definition
Natural plant compounds having basic character and containing at least one nitrogen atom in a heterocyclic ring.
This definition is not entirely accurate due to exceptions:
| Exception Type | Example | Reason |
|---|---|---|
| Alkaloids that don't fit the rule | Piperine | It is a neutral compound, not basic. |
| Compounds that fit the rule but aren't Alkaloids | Purine (and derivatives) | They fit the definition exactly but are not classified as true alkaloids. |
Source
Found mainly in the plant kingdom.
Distribution
Examples
| Plant | Alkaloids Present |
|---|---|
| Opium | Morphine, Papaverine |
| Cinchona | Quinine, Cinchonine |
Alkaloids are classified mainly based on the type of heterocyclic ring present in their structure.
| Sr. No. | Class of Alkaloid | Characteristic Ring | Example(s) |
|---|---|---|---|
| 1 | Piperidine alkaloids | Piperidine ring | Coniine |
| 2 | Pyrrole / Pyrrolidine–Pyridine alkaloids | Pyrrole & Pyridine rings | Nicotine |
| 3 | Pyrrolidine alkaloids | Pyrrolidine ring | Hygrine |
| 4 | Tropane alkaloids | Tropane ring | Atropine, Cocaine |
| 5 | Quinoline alkaloids | Quinoline ring | Quinine, Cinchonine |
| 6 | Isoquinoline alkaloids | Isoquinoline ring | Papaverine |
| 7 | Phenanthrene alkaloids | Phenanthrene nucleus | Morphine |
| Ring Type | Example |
|---|---|
| Piperidine | Coniine |
| Pyrrolidine–Pyridine | Nicotine |
| Pyrrolidine | Hygrine |
| Tropane | Atropine, Cocaine |
| Quinoline | Quinine, Cinchonine |
| Isoquinoline | Papaverine |
| Phenanthrene | Morphine |
Order Trick (Classes)
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Alkaloids Overview is a fundamental concept in organic chemistry. Understanding the mechanisms, reaction conditions, and stereo-chemical outcomes is crucial for mastering organic chemistry. Our curated resources provide step-by-step visualizations to help you excel.
SELF TEST
What are alkaloids generally characterized as?
LEARNING SUPPORT
Alkaloids are naturally occurring, basic, nitrogen-containing organic compounds isolated mainly from plants, which show physiological activity.
Ladenburg defined alkaloids as natural plant compounds having a basic character and containing at least one nitrogen atom in a heterocyclic ring.
Yes, Piperine is an alkaloid but it is neutral, not basic. Conversely, Purine fits the definition exactly but is not classified as a true alkaloid.