Halo Alkane And Halo Arene || Lecture 13 || Stereochemical Aspect of Nucleophilic Substitution Rxn
Channel: Girija Nanda Das
Date: 24/05/2020

Define The Following Stereochemical Terms :

Plane polarised light , Optical activity, chirality, inversion, retention, racemization, Enantiomers, diastereomers :

SOME BASIC CONCEPT OF OPTICAL ISOMERISM:-

          (i). SN2 reaction proceeds with inversion of configuration

         (ii).  SN1 reaction proceeds with racemization.

Plane Polarized Light:-
Ordinary light have e.m. waves in in different directions (e.m→ electromagnetic). Thus such a beam of light which has vibration of EM waves only in one plane is called Plane Polarized Light.

Optical Activity/Optically Active Substances:-
Such substances which can rotate the plane polarized light are called optically active substances and the property of a substance to rotate the plane polarized light light is called the Optical Activity.

Dextrorotatary:-
A substance which rotates plane of polarized light towards right in clockwise direction is called Dextrorotary (+)

Leavorotatory:-
A substance which rotates the plane polarized light towards left is known as a Leavorotory substance (-)

Optical Isomerism:-
The leavoratary (-)andDextrotatory (+) isomers of an optically active compound are called the optical isomers and phenomena is called as Optical Isomerism.

Chiral Molecules:-
Objects or Molecules which are non superimposable on their mirror images are called Chiral Molecules and this properties is known as Chirality.

Assymtrical Molecule:-
The molecule which have an Assymtric carbon atom (such that all the group or atom attached to carbon are different) is called Assymeterical molecule.

Example:-

SOME BASIC CONCEPT OF OPTICAL ISOMERISM-(II)

Enantiomers:-
Optical isomers which are the non superimpossible mirror images of each other are called as the Enantiomers

Example:-

Racemic Mixture:-
A mixture of the equal Amounts of the two enantiomers is called the Racemic Mixture or Racemic Modification.

Racemization:-
The process of conversion of one entiomer (+ or -) into a Racemic Mixture is called Racemisation

Retention:-
If in a chemical reaction the special arrangement of bonds at an assymteric centre remains preserve than it would be known as Retention of Configuration.

Example:-

SOME BASIC CONCEPT OF OPTICAL ISOMERISM-(III)

Inversion:-
If the position of the substituent is get changed by 180° than it would be known as inversion of mixture
Example:-

Stereochemistry of SN2 Reaction:-
SN2 Reactions of optically active alkyl halide are always accompanied by inversion of configuration at the asymmetric centre.

Example:-

Stereochemistry of SN1 Reaction:-
In SN1 reaction if the alkyl halide is optically active then the product will be us a racemic mixture. Thus SN1reaction always accompanied Racemization.
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Q.   Draw structures of possible enantiomers of 3 –methylpent–1–ene.

Ans.     The enantiomers of 3 – methylpent – l – ene are

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