Provide a rationale for why polar protic solvents such as water are not favorabl
ID: 959657 • Letter: P
Question
Provide a rationale for why polar protic solvents such as water are not favorable for the S_N 2 reaction and aprotic solvents such as DMF is favorable for the S_N 2 reaction. Be specific in your explanation. What would be the experimental impact of increasing the concentration of the S_N 2 reaction by a factor of 4? Provide a detailed rationale for your prediction. From an experimental standpoint, would the reaction be more favorable had 1-iodobutanc had been used instead of 1 -bromobutane? Provide a rationale for your answer.Explanation / Answer
(1) Normally,SN2 process involving reaction of anionic nucleophiles with alkylhalides is suppressed in the presence of polar protic solvents(such as water), since a polar protic solvent will interact ( through hydrogen bonding ) more favourably with anionic nucleophiles ( and makes them less reactive ) than with the transition state.Therefore polar protic solvents slow down the reaction. However, polar aprotic solvents are not able to form hydrogen bonding with anionic nucleophiles ,as a result, nucleophiles aremore reactive.
(2) With increase in concentration of SN2 by a factor of 4, then rate of the reaction also increases by the same.
(3) Yes, the reaction would be more favourable if we had used 1- iodobutane instead of 1-bromobutane.
reactivity order of alkyl halides is R-I > R-Br > R-Cl > > R-F
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