Short answer question $($Unit $7)$ Substitution reaction

Differentiate between base and nucleophile. Why iodine become better nucleophile in polar protic solvents even it is weaker base.

Differentiate between SN$2$ and SN$1$ reaction. Show the stereochemistry involved for the SN$1$ and SN$2$ reaction.

Write the factors affecting the substitution reaction. Explain any one in details.

Hint: structure of alkyl halide

Reactivity of nucleophile

Concentration of nucleophile

Solvent of the reaction

Write any two$-$substitution reaction of alkyl halides. Hint:

Explain why the reactivity is more for primary alkyl halide in SN$2$ and tertiary alkyl halide in SN$1$ reaction?