EXP20 - Fijany 56 Layla Fijany Chem 12A T/TH 5-10pm...

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Fijany Layla Fijany Chem 12A T/TH 5-10pm 11/2/2011 Experiment 20: Nucleophilic Substitution Reactions Purpose : To compare relative nucleophilicities of chloride ions and bromide ions toward the following alcohols: 1-butanol, 2-butanol and 2-methyl-2-propanol. Introduction: Substitution reactions are an important class of reactions because of their synthetic utility and importance in understanding the mechanism of a variety of organic reactions. Substitution reactions allow the introduction of a variety of functional groups into organic molecules. Chemists have studied the mechanism of substitution reactions in great detail. The results of these studies have indicated that substitution reactions can be broadly divided into two mechanistic types, called S N 2 and S N 1. S N 2 (Substitution,Nucleophilic, 2nd order) reactions proceed via a one step mechanism in which the incoming nucleophile attacks the electrophilic carbon center from the side opposite the leaving group. This reaction mechanism implies that the stereochemistry of a chiral center will be inverted. Since the reaction occurs in one step without the formation of an intermediate, and both the nucleophile and the electrophile are involved in the formation of the transition state, the reaction is second order overall: rate =[RX][:Nu] S N 1 reactions (Substitution,Nucleophilic, 1st order) proceed via two steps: (1) slow dissociation of the C-X bond to form an intermediate carbocation and (2) a fast second step in which the C-Nu bond is formed. Since only RX is involved in the slow step, the reaction is first order overall: rate =k[RX]. Since the intermediate carbocation is trigonal planar, the nucleophile can attack with equal probability from above or below. This will result in a racemate, of a chiral center, since equal amounts of each enantiomer will result. Hypothesis: The greater amounts of calkyl hloride formed in each reaction, the stronger nucleophilicity of the chloride ions; the more alkyl bromide formed, the stronger nucleophilicity of the bromide ions Set Up: List of Reagents FW (g/mol) BP (˚C) MP (˚C) Density (g/cm 3 ) Other (hazards, uses, etc) 1-Butanol (C 4 H 10 O): 74.14 118 -90 0.81 - extremely irritating to eyes, 56
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Fijany inhalation may cause sore throat or dizziness; partially sol in water; used as artificial flavorant in butter,
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EXP20 - Fijany 56 Layla Fijany Chem 12A T/TH 5-10pm...

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