Chapter 25.7, Problem 9P

Interpretation Introduction

Interpretation:

The isoprene unit in $\text{β-carotene}$ and the carbon which joined by the tail to tail link between isoprene unit is to be identified.

Concept introduction:

The terpenes are the repeating isoprene units.

The isoprene unit is nothing but the carbon skeleton of isoprene without double bonds.

The isoprene molecule has head and tail. The structure of isoprene $\left(\text{2-methyl-1,3-butadiene}\right)$ is shown below:

The isoprene units are together linked in head-to-tail configuration. The tail of the first isoprene molecule joins with the head of the second isoprene molecule.

In higher terpenes, tail-to-tail linkage can also occur. The tail of the first isoprene molecule joins with the tail of the second isoprene molecule.

As the terpenes forms by isomerization of isoprene unit, both the double bonds of isoprene may not be present in the structure of terpenes.

On the basis of number of isoprene units ${{\text{(C}}_{\text{5}}{\text{H}}_{\text{8}}\text{)}}_{\text{n}}$ or number of carbon atoms, the terpenes are classified as monoterpenes, sesquiterpenes, diterpenes, triterpenes, and tetraterpenes.