Factors favoring SN1 AND SN2 Mechanisms:

Nature of alkyl halide

If the alkyl halide is primary, it reacts through SN² and if it is tertiary, it reacts through SN¹ mechanism. 2^° Alkyl halide react through both mechanisms.

Nature of nucleophile

Strong nucleophiles favour SN² mechanism whereas weak nuclephiles favour SN¹mechanism.

Concentration of nucleophile

High concentration of nucleophile favours SN², while low concentration favours SN¹ mechanism.

Nature of solvent

Polar solvents favour SN¹ mechanism as they can cause dissociation of alkyl halide and thus facilitate the formation of carbocation. Solvents of low polarity favour SN² mechanism.

              Reduction of chlorobenzene

With LiAlH₄ or nickel aluminium alloy (Ni-Al), haloarenes undergo reduction to hydrocarbons in the presence of an alkali.