Question

How many isoprene units are present in abscisic acid?
A) Three
B) Two
C) Four
D) Five

Answer 1

Hint: Abscisic acid is a hormone found in a plant. It has a function in the development plant including the seeds and bud dormancy. The natural Terpenoids contain the isoprene units. The isoprene unit is a carbon skeleton. It is also known as the 2-methyl-1, 3-butadiene and has the formula as $\text{ C}{{\text{H}}_{\text{2}}}\text{=C(C}{{\text{H}}_{\text{3}}}\text{)}-\text{CH=C}{{\text{H}}_{\text{2}}}\text{ }$ .

Complete Solution :
The isoprene unit is obtained in the alkaloids. It has the formula of 2-methyl-1, 3-butadiene. The chemical formula of the isoprene unit is $\text{ C}{{\text{H}}_{\text{2}}}\text{=C(C}{{\text{H}}_{\text{3}}}\text{)}-\text{CH=C}{{\text{H}}_{\text{2}}}\text{ }$. The abscisic acid has the molecular formula of $\text{ }{{\text{C}}_{\text{15}}}{{\text{H}}_{\text{24}}}\text{ }$ and these are called the sesquiterpene.
- Now, first, we will draw the structure of the isoprene unit, or we can say 2-methyl-1, 3-butadiene.
The structure can be represented as:

- We can see that the methyl group is attached at 2 positions, and the two methylene groups are attached at 1, and 3 positions, and it represents the butadiene.
- Now, further, we have the structure of abscisic acid. It is abbreviated as ABA.
The structure can be represented as:
   

- The Abscisic acid compound is seen to be composed of three isoprene units. The isoprene units in the ABA are represented as follows:

Thus, the abscisic acid contains the three isoprene units .
So, the correct answer is “Option A”.

Note: There are various natural compounds which contain the isoprene units. Terpenoids are the class of organic compounds that contain the isoprene units. It can be sometimes difficult to identify the isoprene units in the compound. The natural products containing isoprene units are classified based on the number of isoprene units in it.

Terpene	Isoprene units
Hemiterpenoids	1
Monoterpenoids	2
Sesquiterpenoids	3
Diterpenoids	4
Sesterterpenoid	5
Triterpenoids	6
Tetraterpenoids	8
Polyterpenoid	More than 8.