Chapter 5, Problem 8E

(a)

Interpretation Introduction

Interpretation: The reasonable mechanism for product B in reaction below should be drawn.

  

Concept introduction:When one single structure is unable to describe all the properties of single molecule, a phenomenon called resonance comes into play. This arises when two or more than two Lewis structures are possible for one molecule. All such structures are called resonating structures and have same placement of atoms in them but these have different locations of bond pairs and lone pairs. The resonating structures are inter-convertible with each other. The resultant of all the resonating or contributing structures is called the resonance hybrid.

Rules to form resonance structure are as follows:

1. Use arrow types 1 and 2 for resonance structure of anions in movement of negative charge. Arrow type 1 shows the movement of lone pair toward adjacent atom and then converted into $\text{π}$ bond. Arrow type 2 shows the movement of $\text{π}$ electron pair from double bond towards adjacent carbon and then converted into lone pair.

2. Use only arrow type 3 to move a positive charge for resonance structure of cations. Arrow type 3 is used to move $\text{π}$ electron pair towards adjacent single bonds.

3. The sigma bond should not be broken. Any atom must not move from its place and total number of electrons must be same in all resonance structures.

(b)

Interpretation Introduction

Interpretation: The ratio $2:1$ of yield of products A and B in reaction below should be explained.

  

Concept introduction:When one single structure is unable to describe all the properties of single molecule, a phenomenon called resonance comes into play. This arises when two or more than two Lewis structures are possible for one molecule. All such structures are called resonating structures and have same placement of atoms in them but these have different locations of bond pairs and lone pairs. The resonating structures are inter-convertible with each other. The resultant of all the resonating or contributing structures is called the resonance hybrid.

Rules to form resonance structure are as follows:

1. Use arrow types 1 and 2 for resonance structure of anions in movement of negative charge. Arrow type 1 shows the movement of lone pair toward adjacent atom and then converted into $\text{π}$ bond. Arrow type 2 shows the movement of $\text{π}$ electron pair from double bond towards adjacent carbon and then converted into lone pair.

2. Use only arrow type 3 to move a positive charge for resonance structure of cations. Arrow type 3 is used to move $\text{π}$ electron pair towards adjacent single bonds.

3. The sigma bond should not be broken. Any atom must not move from its place and total number of electrons must be same in all resonance structures.