Chapter 29, Problem 18P

Locate the isoprene units in each compound.

a. b.

Interpretation Introduction

(a)

Interpretation: The isoprene units in the given compound are to be located.

Concept introduction: An isoprene unit possesses following properties.

➢ It may either consist of $\text{C}-\text{C}\text{σ}$ bonds only or $\text{π}$ bonds at any position.

➢ It is always connected by one or more $\text{C}-\text{C}$ bonds.

➢ Each isoprene unit is consist of $5\text{C's}$.

➢ While locating an isoprene unit, the presence of heteroatoms is ignored.

Answer to Problem 18P

The isoprene units in the given terpene ($\text{α}$-pinene) are located as,

Explanation of Solution

The given compound ($\text{α}$-pinene) is a terpene. Its structure is in ball-and stick form. It is converted into skeletal structure by replacing black ball with $\text{C}$, and gray ball with $\text{H}$. The skeletal structure of $\text{α}$-pinene is,

Figure 1

Terpenes are composed of repeating five-carbon units. These units are called isoprene units.

Figure 2

An isoprene unit possesses following properties.

➢ It involves one branched carbon and $\text{4}\text{C's}$ in a row.

➢ It may either consist of $\text{C}-\text{C}\text{σ}$ bonds only or $\text{π}$ bonds at any position.

➢ It is always connected by one or more $\text{C}-\text{C}$ bonds.

➢ Each isoprene unit is consist of $5\text{C's}$, with $\text{4}\text{C's}$ in a row and one-carbon branch on a middle carbon.

➢ While locating an isoprene unit, the presence of heteroatoms is ignored.

The isoprene units in the given terpene ($\text{α}$-pinene) are located as,

Figure 3

Conclusion

The isoprene units in the given compound ($\text{α}$-pinene) are located in Figure 3.

Interpretation Introduction

(b)

Interpretation: The isoprene units in the given compound are to be located.

Concept introduction: An isoprene unit possesses following properties.

➢ It may either consist of $\text{C}-\text{C}\text{σ}$ bonds only or $\text{π}$ bonds at any position.

➢ It is always connected by one or more $\text{C}-\text{C}$ bonds.

➢ Each isoprene unit is consist of $5\text{C's}$.

➢ While locating an isoprene unit, the presence of heteroatoms is ignored.

Answer to Problem 18P

The isoprene units in the given terpene (humulene) are located as,

Explanation of Solution

The given compound (humulene) is a terpene. Its structure is in ball-and stick form. It is converted into skeletal structure by replacing black ball with $\text{C}$, and gray ball with $\text{H}$. The skeletal structure of humulene is,

Figure 4

Terpenes are composed of repeating five-carbon units. These units are called isoprene units.

Figure 2

An isoprene unit possesses following properties.

➢ It involves one branched carbon and $\text{4}\text{C's}$ in a row.

➢ It may either consist of $\text{C}-\text{C}\text{σ}$ bonds only or $\text{π}$ bonds at any position.

➢ It is always connected by one or more $\text{C}-\text{C}$ bonds.

➢ Each isoprene unit is consist of $5\text{C's}$, with $\text{4}\text{C's}$ in a row and one-carbon branch on a middle carbon.

➢ While locating an isoprene unit, the presence of heteroatoms is ignored.

The isoprene units in the given terpene (humulene) are located as,

Figure 5

Conclusion

The isoprene units in the given compound (humulene) are located in Figure 5.