Chapter 6, Problem 33PP

Interpretation Introduction

Interpretation:

The sequences of arrow-pushing pattern in the given reactions have to be identified and compared.

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.

In nucleophilic substitution reaction a nucleophile is the species with an unshared electron pair which reacts with an electron deficient carbon. And so the leaving group is substituted by a nucleophile.

Ipso substitution reaction: It is the one of the aromatic substitution reaction in which both the substituent (nucleophile and the parent substituent) present in the same ring position in an intermediate compound. Finally the parent substituent leave from the intermediate leads to the formation of product.

The mechanism of desulfonation curved arrow pattern is given below.