Impacts of Polarity

Impacts of Polarity - Impacts of Polarity Protic solvents...

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Impacts of Polarity Protic solvents that contain –OH or NHx groups are generally poor solvents for Sn2 rxns b/c the solvent molecules arrange in a way around the nucleophile that they form a “solvent cage” o Decrease the ground-state energy of the nucleophile b/c of the better stabilization of the charge o Good solvents for Sn1 rxn Stabilize the transition state that is highly charged and the intermediate carbocation, and therefore increase the rate of the rxn. Polar aprotic solvents like acetonitrile, demethylformamide and dimethylsulfoxide increase the ground-state energy of the nucleophile. o b/c they solvate metal cations rather than the nucleophilic anion, which remains “naked” and therefore more reactive. Phase transfer rxns circumvent the problem of low reactivity of the nucleophile by transferring the nucleophile from a protic to an aprotic solvent. Polar aprotic solvents + strong nu Sn2 mechanism Polar protic solvents + weak nu Sn1 mech. Drying Agents
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This note was uploaded on 03/31/2009 for the course CHEM Chem 30BL taught by Professor Bacher during the Winter '09 term at UCLA.

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Impacts of Polarity - Impacts of Polarity Protic solvents...

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