Isomers are different compounds that have the same molecular formula.

Structural isomers: 
Structural isomers have the same molecular formula but different connectivity, meaning that their atoms are connected in a different order. Examples of the structural isomers for the following;


Stereoisomers are not constitutional isomers. Stereoisomers have the atoms connected in the same sequence, but they differ in the arrangement of the atoms in space. Each stereoisomer has a unique configuration (either R or S) that can only be converted the different configuration by chemical means that is breaking and making of bonds. Stereoisomers are further categorised into (a) conformational isomers (b) configurational isomers

Configurational isomers of further divided into two categories enantiomers and diastereomers;
ENANTIOMERS : Enantiomers are stereoisomers whose molecules are non-superimposible mirror images of each other.
DIASTEREOMERS : Diastereomers are stereoisomers whose molecules are not Mirrror Images of each other

The Reimer-Tiemann reaction: Reaction and its Mechanism

Reimer-Tiemann Reaction Phenols on reaction with chloroform in the presence of sodium hydroxide (or potassium hydroxide) solution give hydro...