Question

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Answer 1

Substitution Reactions are those reactions in which one nucleophile replaces another nucleophile present on a substrate. These reactions can take place via two different mechanism i.e SN¹ or SN². In SN¹ substitution reactions the leaving group leaves first forming a carbocation and nucleophile attacks carbocation in the second step. While in SN² reactions the addition of Nucleophile and leaving of leaving group take place simultaneously.
 
Example:
                        OH⁻  +  CH₃-Br     →     CH₃-OH  +  Br⁻

In above reaction,

                   OH⁻  = Incoming Nucleophile

                   CH₃-Br  =  Substrate

                   CH₃-OH  =  Product

                   Br⁻  =  Leaving group

Organic reactions are typically slower than ionic reactions because in organic compounds the covalent bonds are first broken, this breaking of bonds is a slower step, while, in ionic compounds no bond breakage is required as it consists of ions, so only bond formation takes place which is a quicker and fast step.