Introduction of Reaction mechanism I

Concepts to understand 'Reaction mechanism'

A) Electronic displacement in co-valent bonds

Displacement depends on the following factors- 

a) Inductive effect or I-effect

Partial displacement of sigma electrons (σ- e^-s) towards more electronegative atom is called Inductive effect or I-effect.

Inductive effect is a permanent effect.

b) Resonance or Mesomeric effect

Complete transfer (delocalization) of Pi-electrons (π-e^-s) is called Resonance.

Resonance is a permanent effect.

c) Hyper conjugation effect or No bond resonance or H-effect

Complete transfer (delocalization) of Pi-electrons (π-e^-s) is called Hyper conjugation effect.

d) Electromeric effect

Complete transfer of Pi-electrons (π-e^-s) of multiple bond in presence of reagent i.e. on demand of reagent.

It is temporary effect.

B) Bond cleavage

a) Homolysis

Intermediate free radicals are formed.

Conditions

High temperature

Presence of non-polar substance

Presence of non-polar solvent

Presence of peroxide

Presence of UV light

Etc.

b) Hetrolysis

Intermediate Cation & Anion are formed.

Conditions

Low temperature

Presence of polar substance

Presence of polar solvent

Etc.

C) Nature of reagent

a) Electrophile

Positively charged or electron deficient or electron attracting species.

b) Nucleophile

Negatively charged or electron rich or nucleus attracting species.