These free B.Pharm notes on tannins, terpenoids, volatile oils and resins cover chapter 18 of Introduction to Pharmacognosy, a first-semester subject. Read the key points below, then study the complete chapter PDF. You can browse every chapter in the Introduction to Pharmacognosy category.
Table of Contents
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Overview of tannins, terpenoids, volatile oils and resins
This chapter covers four groups of plant constituents: tannins, volatile oils, terpenoids and resins. For each it explains the definition, classification, occurrence, extraction or isolation, chemical tests, functions in plants and therapeutic uses, including the isoprene rule and the classification of terpenoids by carbon number.
Key points on tannins, terpenoids, volatile oils and resins
- Tannins are complex, non-nitrogenous polyphenolic plant compounds with astringent properties, and they are identified by the Goldbeater’s skin test because they bind proteins.
- Hydrolysable tannins are broken by dilute acids or tannase and give a blue-black colour with ferric chloride, while condensed tannins resist acids and give a green colour.
- Volatile oils are aromatic plant constituents made mainly of terpenoids and their oxygenated derivatives, and they evaporate at ordinary temperature without leaving a permanent grease stain.
- Terpenoids are built from repeating five-carbon isoprene units with the general formula (C5H8)n, and are classified by carbon number as mono-, sesqui-, di-, sester-, tri-, tetra- and polyterpenoids.
- Resins are complex, amorphous, non-nitrogenous plant products that soften on heating, are insoluble in water, and dissolve in alcohol, ether, benzene and chloroform.
Relevance to pharmacy practice
These constituents are the active parts of many familiar crude drugs, such as clove oil, catechu, benzoin and the antimalarial artemisinin. Pharmacists use this knowledge to identify drugs, understand their uses, and advise patients on products used for wounds, digestion, cough and pain.
Every chapter in this subject builds on the one before it, so do not skip topics that look simple. Definitions, classifications and examples are the parts that examiners return to most often, and a clear understanding here will also make later subjects easier to follow in the coming semesters.
Frequently asked questions on tannins, terpenoids, volatile oils and resins
What is the difference between true tannins and pseudotannins?
True tannins are high molecular weight polyphenols that give a positive Goldbeater’s skin test and convert hide to leather. Pseudotannins are simple low molecular weight phenols with a negative test, such as gallic acid.
What is the isoprene rule?
Otto Wallach observed that many terpenoids give isoprene units (C5H8) on thermal decomposition, so terpenoids are formed by joining two or more isoprene units, usually linked head to tail.
How are volatile oils extracted?
The main methods are distillation (hydrodistillation or steam distillation), scarification or expression for citrus oils, extraction by non-volatile solvents such as enfleurage, and extraction by volatile solvents.
Quick revision checklist
Use this self-test after reading the chapter on tannins, terpenoids, volatile oils and resins. If you can do all of the following without looking at your notes, you are ready for the exam.
- I can explain: the classification of tannins
- I can explain: the tests for tannins
- I can explain: methods of extracting volatile oils
- I can explain: the isoprene rule and terpenoid classes
- I can explain: the classification of resins
Study and exam tips
Start by reading the chapter once for the overall idea, then revise tannins, terpenoids, volatile oils and resins using headings, definitions, classifications and examples. Short-answer questions in the university exam usually ask for definitions, features, advantages, disadvantages and examples, so write these in your own words and practise drawing the tables and flow charts that the chapter has.
For wider reading, standard textbooks and open resources such as the NCBI Bookshelf help you confirm terms and see more examples. Revise tannins, terpenoids, volatile oils and resins again a day later and again a week later, because spaced revision improves long-term memory.
This page is part of the Introduction to Pharmacognosy series for first-semester B.Pharm students on B.Pharm Guru, where every chapter has a short summary and a full PDF. Bookmark this page and share it with classmates who are preparing for the same exam.
Related notes: 20. TYPES OF DOSAGE FORMS IN AYUSH MEDICINES, 21. ROLE OF PHARMACOGNOSY IN ALLOPATHY AND TRADITIONAL SYSTEMS OF MEDICINE.
Next: 19. TRADITIONAL SYSTEMS OF MEDICINE. Back to the Introduction to Pharmacognosy category.
