Chapter 7, Problem 2LGP

Interpretation Introduction

Interpretation:

The given reaction using mechanistic arguments involving Newman projections is to be explained.

Concept Introduction:

▸ Newman projected two types of spatial arrangements of molecules: staggered and eclipsed Newman projections.

▸ Staggered conformation: It is the arrangement of atoms or groups of atoms in a molecule resulting in a ${60}^{\circ }$ dihedral angle. It is also called anti-coplanar transition or anti-conformation. It has low potential energy because of less torsional strain and hence, is more stable

▸ Eclipsed conformation: It is the arrangement of atoms or groups of atoms in a molecule resulting in a $0^{\circ }$ dihedral angle. It is also called syn-planar transition or gauche-conformation. It has high potential energy because of high torsional strain and hence, is less stable.

▸ The molecules which are non-superimposable or not identical with their mirror images are known as chiral molecules.

▸ A pair of two mirror images which are non-identical is known as enantiomers which are optically active.

▸ The objects or molecules which are superimposable with their mirror images are achiral objects or molecules and these objects have a centre of symmetry or plane of symmetry.

▸ The achiral compounds in which plane of symmetry is present internally and consists of chiral centres are known as meso compounds but they are optically inactive.

▸ The stereoisomers which are non-superimposable on each other and not mirror images of each other are known as diastereomers.

▸ Chiral molecules are capable of rotating plane polarized light

▸ The molecules which are superimposable or identical with their mirror images are known as achiral molecules, and achiral molecules are not capable of rotating the plane-polarised light.

▸ Priority is given to all the four group attached to the chirality center.

▸ Priority is assigned on the basis of the atomic number of the atom. Higher the atomic number, higher will be its priority.

▸ If priority cannot be assigned according to atomic mass, then, it is assigned according to first point of difference.

▸ After assigning priority to the four groups, rotate the molecule such that fourth priority group is away from the observer.

▸ Now, move from a to b to c; if the direction is clockwise, then the chiral center designated as $\left(R\right)$ and if the direction is anticlockwise, then the chiral center designated as $\left(S\right)$.