Chapter 21.3, Problem 16ATS

(a)

Interpretation Introduction

Interpretation: Without any stereochemistry, the expected aldol addition product for the given aldehyde has to be drawn.

Concept Introduction:

Aldol addition:

When an aldehyde is treated with aqueous sodium hydroxide, the major product has the aldehydic group and a hydroxyl group. It is therefore called an “aldol” (“ald” for aldehyde and “ol” for alcohol). In the product, it is important to note that hydroxy group should be located in the $\beta$ (beta) -position relative to the carbonyl group. Thus the product aldol is also known as $\beta$- hydroxy aldehyde.

Example:

(b)

Interpretation Introduction

Interpretation: The all possible stereoisomers for the product obtained in the subpart (a) have to be drawn.

Concept Introduction:

Stereocenters:

It refers to the carbon that have four different groups attached to it. It is also known as chiral centre.

Stereoisomers

The stereoisomers are the compounds with same molecular formula but with different spatial arrangement of atoms.

Example:

The stereoisomers of Leucine:

Finding the number of possible stereoisomers:

The number of stereocenters in the compound has to be considered as ‘n’.

Then the possible number of stereoisomers of the compound should be given using the expression--$2^n$.

Example:

The maximum number of stereoisomers for $\text{Leucine}$: ${\text{2}}^{\text{n}}$

Where,

$\begin{array}{c}\text{n=}\text{no}\text{.}\text{of}\text{stereocenters}\\ \text{n=}\text{2}\\ {\text{2}}^{\text{n}}={\text{2}}^1\\ =2\end{array}$

So, a maximum of two stereoisomers are possible for $\text{Leucine}$.

The stereoisomers of $\text{Leucine}$: