→ Reactivity order of primary secondary and tertiary halides toward SN
2 reaction is CH
3-X > 1º - halide > 2º - halide > 3º - halide.
→ The presence of bulky substituents on or near the carbon atom have a dramatic inhibiting effect.
→ Of the simple alkyl halides, methyl halides react most rapidly in SN
2 reactions because there are only three small hydrogen atoms.
→ Tertiary halides are the least reactive because bulky groups hinder the approach nucleophiles.
→ Thus, the order of reactivity followed is: Primary halide > Secondary halide > Tertiary halide.

