Chapter 5, Problem 5.33P

(a)

Interpretation Introduction

Interpretation:

Two different coiling patterns of the carbon skeleton of farnesol that can lead to form santonin have to be shown.

Concept Introduction:

Terpenes are made by joining five-carbon units, usually in a head to tail-fashion.

Isoprene unit:

Branched end of isoprene – Head

Unbranched end of isoprene - Tail

(b)

Interpretation Introduction

Interpretation:

Chiral carbon atoms present in santonin has to be labelled and the number of possible stereoisomers for santonin has to be given.

Concept Introduction:

Chirality: It refers to a Carbon atom in a molecule that contains four different substituents.

Stereoisomers: Two compounds with same molecular formula but different in their orientation are considered as isomers.

Number of possible stereoisomers for a compound can be determined as,

$\begin{array}{l}{\text{No of possible stereoisomers = 2}}^{\text{n}}\\ \\ \text{where,}\\ \text{n = no}\text{. of chiral atoms in the compound}\end{array}$

(c)

Interpretation Introduction

Interpretation:

Index of hydrogen deficiency has to be calculated for santonin.

Concept Introduction:

Index of hydrogen deficiency in a molecule is the total number of rings and $\text{π-}$ bonds.

$\begin{array}{l}\text{Index of hydrogen deficiency}=\frac{\left({\text{H}}_{\text{reference}}-{\text{H}}_{\text{molecule}}\right)}{2}\\ where,\\ {\text{H}}_{\text{molecule}}=\text{ Number of hydrogens in the given molecule}\text{.}\\ {\text{H}}_{\text{reference}}=\text{Number of hydrogens in the acyclicalkane }\\ \text{having same number of carbon atoms}\left({\text{C}}_{\text{n}}{\text{H}}_{\text{2n+2}}\right)\text{.}\end{array}$

The molecular formula of the reference hydrocarbon has to be adjusted if atoms other than carbon and hydrogen are present.

• • If Group 7 elements like $\text{F, Cl, Br, I}$ is present, then the halide atom is replaced by hydrogen. For example, the molecular formula of the acyclic monochloroalkane is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n+1}}Cl$, then the molecular formula should be taken as ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n+2}}$.
• • If Group 6 elements like $\text{O, S, Se}$ are present, then there is no change in the molecular formula.
• • If Group 5 elements like $\text{N, P, As}$ are present, then one hydrogen should be added to the molecular formula.