Question

Among the following, the total number of terpenes (terpenoids) is ________. 

Hint:

To identify terpenes, count carbons and check for $\mathrm{C_5H_8}$ repeating units connected head-to-tail. Terpenoids may include oxygenated derivatives of terpenes.

Answer 1

Correct Answer: 7

Step 1: Recall the definition of terpenes.
Terpenes (or terpenoids) are natural compounds built from isoprene ($\mathrm{C_5H_8}$) units.
The general formula is $(\mathrm{C_5H_8})_n$, where $n = 1, 2, 3, \dots$ representing mono-, sesqui-, di-, tri-, and tetraterpenes.
Step 2: Identify compounds based on isoprene rule.
Each compound is examined for the number of carbon atoms and structural repetition of $\mathrm{C_5H_8}$ units.
Compounds satisfying the isoprene rule (number of carbons = multiple of 5 and connectivity via head–tail linkages) are considered terpenes/terpenoids.
Step 3: Classification.
- Compounds with 10C → monoterpenes (2 isoprene units).
- Compounds with 15C → sesquiterpenes (3 isoprene units).
- Compounds with 20C → diterpenes (4 isoprene units).
- Compounds with 30C → triterpenes (6 isoprene units).
- Compounds with 40C → tetraterpenes (8 isoprene units).
After analyzing the structures given, 7 compounds satisfy the isoprene rule (terpenoid skeletons), while the others are non-terpenoid (contain carbonyl or aromatic interruptions violating head–tail linkage).
Step 4: Conclusion.
Hence, the total number of terpenes (terpenoids) among the given compounds is 7.