1058-RG2-10 - Chem 1058 J. Walcott LEARNING STRATEGIES...

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Chem 1058 J. Walcott LEARNING STRATEGIES CENTER Spring 2010 Review Guide #2 Lectures: 2/1/10 – 2/5/10 Chapters 14 and 15 I. Electrophilic Aromatic Substitution Reactions continued A. The general mechanism of electrophilic aromatic substitution consists of three steps: 1. A strong electrophile is generated. 2. Benzene reacts with the electrophile to form a resonance stabilized carbocation intermediate. 3. Loss of H + from the carbocation intermediate restores the aromatic pi system to give the final substitution product. B. You should know the reagent conditions used, the overall transformation, and the reaction mechanism for the following electrophilic aromatic substituion reactions: bromination, chlorination, nitration, sulfonation, Friedel-Crafts acylation (used to prepare ayrl ketones), and Friedel-Crafts alkylation (used to prepare alkylbenzenes). 1. Friedel-Crafts Acylation a. Excess AlCl 3 is used because the catalyst forms a complex with the carbonyl oxygen. b. Acylation deactivates the benzene ring and no further substitution takes place. 2. Friedel-Crafts Alkylation has limitations a. Polyalkylation can occur, so excess benzene is used as solvent. b. Rearrangements can occur. c. Friedel-Crafts alkylation will not occur on a deactivated benzene ring. 3. Alkylation via Acylation and reduction a. Carbonyls can be reduced by H 2 and Pd/C (neutral) catalyst to a methylene group (-CH 2 -). b. Clemmensen Reduction - Aldehydes and ketones can also be reduced to a methylene group with zinc amalgam in acid (HCl). c. Wolff-Kishner Reduction - Aldehydes or ketones can be reduced to a methylene group
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This note was uploaded on 04/05/2010 for the course CHEM ORGANIC CH taught by Professor Dotsevisogah during the Spring '09 term at Cornell University (Engineering School).

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1058-RG2-10 - Chem 1058 J. Walcott LEARNING STRATEGIES...

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