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12a Sn1 and Sn2. introduction

12a Sn1 and Sn2. introduction - Because SN2 reactions occur...

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Holly Polk 12a Sn1 and Sn2 Reactions Introduction This lab works with alkyl halides in Sn1 and Sn2 reactions. The objective is to determine the reactivities of the different alkyl halides in Sn1 and Sn2 reaction conditions. Whether an alkyl halide will undergo an S N 1 or an S N 2 reaction depends upon a number of factors. Some of the more common factors include the natures of the carbon skeleton, the solvent, the leaving group, and the nature of the nucleophile. The carbon skeleton affects what mechanism the reaction will proceed through. Normally, only compounds that yield 3° (tertiary) carbonications or resonance-stabilized undergo S N 1 mechanisms rather than S N 2 mechanisms. Primary alkyl halides have little inductive stability of their cations and usually undergo S N 2 mechanisms. The solvent also affects which reaction will proceed. Polar protic solvents such as water favor S N 1 reactions, which produce both a cation and an anion during reaction.
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Unformatted text preview: Because SN2 reactions occur via a concerted mechanism (a mechanism which takes place in one step, with bonds breaking and forming at the same time) and no ions form, polar protic solvents would have little effect upon them. The nature of the leaving group also affects which reaction will proceed. In general, good leaving groups form stable ions or molecules upon displacement from the original molecule. Conversely, poor leaving groups form ions of poor stability. Strong bases, such as OH − , NH 2 − , and RO − , make poor leaving groups. Water, which is less basic than a hydroxide ion, is a better leaving group. Poor bases usually make good leaving groups. Because the reaction conditions affect the final product that will form, it is possible to force a nucleophilic substitution reaction to proceed through Sn1 or Sn2 mechanism by changing the reaction conditions....
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