Chapter 3, Problem 3.56P

Interpretation Introduction

Interpretation:

The planar configuration at the nitrogen atom and hindered rotation about the $\text{C}-\text{N}$ bond in amides is to be explained.

Concept introduction:

Geometry of an atom is determined by the number of electron groups around it. For four electron groups, the geometry is tetrahedral. For three electrons groups, the geometry is trigonal planar, and for two electron group, it is linear.

An electron group is a lone pair or a bond. A single bond, a double bond, and a triple bond all count as just one electron group each.

Molecules in which an atom with a lone pair or a multiple bond is present next to a single bond can exhibit resonance.

The groups attached to a single bond can rotate relatively freely around the bond axis as it does not involve any change in the overlap of the bonding orbitals.

Groups attached to a double or triple bond cannot easily rotate around the bond axis as this involves a substantial reduction in overlap of bonding orbitals, equivalent to breaking of one (or two ) bonds.