Chapter 2, Problem 60PP

Interpretation Introduction

Interpretation

The sites of low electron density have to be identified.

Concept Introduction:

Resonance is a method to relating to describe about delocalized electrons inside certain molecules or polyatomic ions where the Lewis structure can’t be expressed.  A molecule or ion containing delocalized electrons can be represented by using several similar structures such structures are called as resonance structures or canonical structures.

The delocalization of electron lowers the potential energy of the substance and making it more stable than any of the contributing structures.  The variation in the potential energy of the actual structure and that of resemblance structure with lowest potential energy is known as resonance energy or delocalization energy.

Electron density is measure of finding an electron at a particular location. In molecules, the electron density is usually seen around the atom.

In case of de-localized system, the electron density is seen over an entire region. In case of compounds with interconnected multiple ring systems, the electron density is higher next to the single bond.

Lone pair:

A lone pair is given by a pair of outer most electrons that are not shared with another atom, otherwise called as non bonding pair.  These are generally found in the valence shell of atom and are identified by Lewis structure.  Pairs of electrons are considered as lone pairs when two electrons are paired and are not participated in chemical bonding. The sum of number of lone pairs and number of bonding electrons equals the total number of outermost electrons around an atom.

Delocalized lone pair:

The lone pair that participates in resonance is called as delocalized lone pair.  The presence of lone pair affects the geometry of the atom.

Localized lone pair:

The lone pair that doesn’t participate in the resonance is called localized lone pair.  The lone pair is not allylic to $\text{π}$ bond.