Lab 7 - Gaurav Singh Brooke Leslie / Chad Landrie 1 April...

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Gaurav Singh Brooke Leslie / Chad Landrie 1 April 2009 Lab Seven: Preparation of Tertiary Alkyl Chlorides by Nucleophilic Aliphatic Substitution. Sodium Iodide and Silver Nitrate Tests for Alkyl Halides Background and Introduction Tertiary alkyl chlorides may be prepared through a S N 1 (unimolecular nucleophilic substitution) mechanism or through a S N 2 (bimolecular nucleophilic substitution). The lab’s main purpose was to determine which mechanism is in fact used; this was done through confirmatory tests. The key difference between the two substitution types is the number of molecules involved in the transition state: S N 1 involes only one molecule in the rate determining step; S N 2, on the other hand, involves two. When a S N 1 reaction is conducted with an alcohol, the hydroxyl group is protonated and leaves as water, leaving a carbocation with a positive charge. The carbocation is more stable and can react faster if it is stabilized by hyperconjugation. Therefore, 3° carbocations will be more stable and thus react faster than a 1° carbocation. Once the carbocation has been formed, it is subject to nucleophilic attack from either the front or the back of the molecule; this produces racemic product yields with two different stereochemistry configurations for the two different products. Figure one, below explains this mechanism visually. The second type of reaction mechanism, S N 2, does not produce a carbocation that is stabilized by hyperconjugation. Instead it involves a direct nucleophilic back-side attack on the carbon which forces out the leaving group. Since there is no hyperconjugation present the
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reaction rates are determined by the ease of which the nucleophile can attack. The attack grows difficult with an increased number of substituents, therefore the order of reactivity is the reverse
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This note was uploaded on 04/14/2010 for the course ENGL 104 taught by Professor Osbourne during the Spring '08 term at A.T. Still University.

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Lab 7 - Gaurav Singh Brooke Leslie / Chad Landrie 1 April...

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