CHE_LAB9(Nuc)

CHE_LAB9(Nuc) - Nucleophilic Substitution of Alkyl Halides...

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Unformatted text preview: Nucleophilic Substitution of Alkyl Halides Experiment #9 Purpose The experiment will evaluate the efficiency of the Sn2 and Sn1 reactions of alkyl halides. The effect of substrate structure, leaving group, temperature, and solvent polarity on the reaction will also be observed. Results and Discussion Sn1 with AgNO 3 Compound Room Temp 50 C Amount Time of Reaction Observations 1-Chlorobutane Slight Slight Little 60s Translucent light cloud 1-Bromobutane Reaction / Good 30s Precipitate at bottom 2-Chlorobutane No Rx Tiny to no Rx None - Tiny 5 min Little to No Rx with heating 2-Bromobutane Instant Rx / Good - Great 20s Precipitate at bottom 1-Chloro-2-Methylpropane Slight Slightly more Little 120s Very light cloud 1-Chloro-2-Butene Instant Rx / Great 20s A lot of precipitate 2-Chloro-2-Methylpropane Instant Rx / Great 30s A lot of precipitate 1-Chloroadamantane No Rx Reaction Little - Good 60s Slight precipitate at 50 C Bromobenzene No Rx No Rx None n/a No reaction 2-Chlorobutane (HOH +EtOH) Slight Rx More Good 120s Moderate Rx when heated AgNO 3 will dissociate and react with several alkyl halides via a Sn1 pathway. The reactions require the formation of an unstable carbocation and a protic polar solvent (EtOH) will help stabilize the unstable positive charge on the carbon. In the case of an aprotic solvent, hydrogen bonding will not be present and decrease the likelihood of a Sn1 reaction. This is shown when the solvent system is altered slightly with HOH. In the reaction with 2-Chlorobutane, the reaction was promoted with the addition of water as a solvent system. HOH exhibits more hydrogen bonds than ethanol and will assist the solvolysis of the alkyl halide. In the case of primary, secondary, and tertiary halides, Sn1 reactions will favor the greater substituted halide. This is shown throughout the experiment with substrates such as 2-Chrloro-2-Methylpropane when compared to substrates such as 1-chlorobutane. The primary halide 1-chlorobutane yielded only small amounts of product while 2-chloro-2-methylpropane, a tertiary halide had large product yields. 2-chlorobutane, a secondary halide was predicted to be the intermediate between yields....
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This note was uploaded on 05/25/2008 for the course CHE 276 taught by Professor Totah during the Fall '07 term at Syracuse.

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CHE_LAB9(Nuc) - Nucleophilic Substitution of Alkyl Halides...

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