Chapter 6, Problem 53IP

(a)

Interpretation Introduction

Interpretation:

All curved arrows that show the entire transformation of compound 1 into 6 have to be drawn and entire sequance of arrow pushing patterns should be identified.

Concept Introduction:

Mechanism of the reaction is the step-by-step description of the process by which reactants are changed into products.

There are only four characteristic patterns, and all ionic mechanisms are simply combinations of these four steps, and they are,

1. (1) Nucleophilic attack

When we identify a nucleophilic site and an electrophilic site, the arrow in the mechanism step shows the nucleophile attacking.

1. (2) Proton transfer
2. (3) Loss of leaving group
3. (4) Rearrangements

Rearrangements will always occur when an alkyl group or hydrogen can shift to form a more stable carbocation. There are mainly two types of rearrangement shifts and they are,

$\begin{array}{l}\text{1, 2-methyl shift}\hfill \\ \text{1, 2-hydride shift}\hfill \end{array}$

Curved arrows show the bonds that are formed and the bonds that are broken in a reaction.

Curved arrows used to understand a reaction mechanism.

Curved arrows are drawn to show how the electrons move as new covalent bonds are formed existing covalent bonds are broken.

Each arrow represents the simultaneous movement of two electrons from a nucleophile towards an electrophile.

Nucleophile: It is negatively charged species which seeks for positive charge and hence donate pair of electrons to positively charged species (electrophiles) which results in the formation of chemical bond.

(b)

Interpretation Introduction

Interpretation:

Nucleophilic and eletrophilic centers in compound 4 has to be identified and use resonance structures to justify why the latter is electron poor.

Concept Introduction:

Electrophile: It is positively charged species which seeks for negative charge and hence accepts pair of electrons from negatively charged species (Nucleophiles) which results in the formation of chemical bond.

Electrophiles have a specific atom or region of the molecule which is electron deficient. This region is called the electrophilic center.

Nucleophile: It is negatively charged species which seeks for positive charge and hence donate pair of electrons to positively charged species (electrophiles) which results in the formation of chemical bond.

Nucleophiles have a specific atom or region of the molecule which is electron excess. This region is called the electrophilic center.

Resonance is an electron displacement effect for stabilizing a molecule through delocalization of bonding electrons in the pi orbital.

Delocalized electrons stabilize a compound. The extra stability gains from having delocalized electrons are called resonance stabilization or resonance energy.

(c)

Interpretation Introduction

Interpretation:

New chiral center which is formed in the conversion of 4 into 5 has to be identified and its configuration has to assigned. It should be explained that why the other possible configuration is not observed.

Concept Introduction:

The stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in different in each isomer.

Chiral centre: A chiral centre is defined as the tetrahedral carbon atom in an organic molecule that is connected to four non-identical groups/substituents. It is sometimes known as a stereo genic centre.

Chirality: The geometric property of molecules where the structure of the molecule and its mirror image are not superimposable is known as chirality. Chiral molecules are optically active and they can rotate the plane polarized light.

R and S nomenclature: it is used to assign the molecule using CIP (Cahn-Ingold-Prelog) rules.

The CIP rules are as follows:

Select the chiral carbon and assign the numbers according to the decreasing atomic mass of atoms attached to it.

If the numbering follows clockwise direction then the molecule is termed as R and if it follows anti-clockwise direction then molecule is termed as S.