CHEM 140A 224 5.Arrange the solvents in order of fastest to slowest for SN1 reactions: (a) fluoromethane, iodomethane, bromomethane; (b) CH3OCH3, hexane, CH3OH 6.Determine whether each of the following reactions will occur faster in a protic or aprotic solvent. Effect of Leaving Group: xSince leaving group departure occurs during the first (or rate-limiting) step of an SN1 reaction, the rate of reaction increases with increasing leaving group ability. In other words, the better the leaving group, the faster the SN1 reaction.Effect of Nucleophile xSince the nucleophile is not involved in the rate-determining step, the concentration or strength (i.e. nucleophilicity) of the nucleophile has no effect on the reaction rate. xHowever, when two or more nucleophiles are present in a reaction, their relative strength may affect the ratio of the products formed. Hence nucleophilicity is only important when there are two or more nucleophiles competing for the same carbocation. 7.5 Effect of Alkyl Group: Carbocation Stability xSN1 reactions occur readily on substrates that form stable carbocations upon departure of the leaving group. xTwo general features that can help stabilize carbocations are hyperconjugation and resonance. 1.Carbocations surrounded by alkyl groups are stabilized through hyperconjugation. -The order of reactivity for alkyl halides is therefore: Tertiary > Secondary > Primary > Methyl -Methyl and primary halides react so slowly that there is essentially no reaction by an SN1 mechanism.