Chapter 23, Problem 23.22P

(a)

Interpretation Introduction

Interpretation:

The functional groups present in desosamine have to be identified.

Concept Introduction:

Amide: One $-N{H}_2$, $-NHR\text{'}$ or $-NR{\text{'}}_2$ group is attached to the carbonyl carbon atom of the compound. It is represented as $RCONR{\text{'}}_2$.

Amines are the derivatives of ammonia $\left(N{H}_3\right)$ with one or more of the hydrogens replaced with a substituent such as an alkyl group.

Depending on the number of carbon side chain of the nitrogen, different types of amines can form.

Hemiacetal is an organic compound with a general formula $R^1{R}^{2}C\left(OH\right)OR$ where R must be always an alkyl group whereas R¹ and R² can be hydrogen or carbon

Alcohol: It is an organic compound where it contains at least one $-OH$ group. It is represented as $ROH$.

(b)

Interpretation Introduction

Interpretation:

Number of chiral centers are present in desosamine has to be determined. Number of possible stereoisomers for desosamine and the number of enantiomers possible has to be determined.

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,

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

Enantiomers: They are chiral molecules whose mirror images are not superimposable.

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

  $\begin{array}{l}{\text{No of possible stereoisomers = 2}}^{\text{n}-1}\left(when\text{ n is even}\right)\\ \\ {\text{No of possible stereoisomers = 2}}^{\text{n}-1}-{\text{2}}^{\text{n/2}-1}\left(when\text{ n is odd}\right)\\ \\ \text{where,}\\ \text{n = no}\text{. of chiral atoms in the compound}\end{array}$

(c)

Interpretation Introduction

Interpretation:

The alternative chair conformations for desosamine have to be drawn.

Concept Introduction:

Drawing Axial and Equatorial substituents:

Each carbon in cyclohexane can bear two substituents. One group is said to occupy an axial position, which is parallel to a vertical axis passing through the center of the ring. The other group is said to occupy an equatorial position, which is positioned approximately along the equator of the ring.

(c)

Interpretation Introduction

Interpretation:

More stable alternative chair conformations for desosamine have to be identified and explained.

Concept Introduction:

Drawing Axial and Equatorial substituents:

Each carbon in cyclohexane can bear two substituents. One group is said to occupy an axial position, which is parallel to a vertical axis passing through the center of the ring. The other group is said to occupy an equatorial position, which is positioned approximately along the equator of the ring.