More stable the carbocation, more the tendency to undergo SN1 reaction. Thus, order of carbocation to undergo SN1 reaction is: Benzyl > Allyl >3∘>2∘>1∘>−CH3 Related Theory The rate of reaction depends on the concentration of the substrate in SN l reaction While In SN, the rate of reaction depends on the concentration of both the substrate and the nucleophile. ! Caution Benzyl carbocation is stabilised by resonance so it will undergo SN I reaction.