lecture 14 given - Lecture 14 Chemistry 310N Organic...

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ecture 14 Lecture 14 Chemistry 310N Organic Chemistry II for Prehealth Professionals Unique number: 53185 Tu,Th 12:30-2:00 pm, Welch 2.224 rofessor: Jonathan Sessler Ph D Professor: Jonathan Sessler, Ph.D. sessler@mail.utexas.edu
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ischer Esterification Fischer Esterification – A key intermediate in Fischer esterification is the tetrahedral carbonyl addition intermediate (TCAI) rmed by addition of ROH to the C=O group formed by addition of ROH to the C=O group. H TCAI CO C H 3 O R O H + H + H O RC O C H 3 O R HOCH 3 + HOH + H
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ey Features of Mechanism Key Features of Mechanism •Activation of carbonyl group by protonation of carbonyl oxygen •Nucleophilic addition of alcohol to carbonyl group forms tetrahedral intermediate •Elimination of water from tetrahedral intermediate stores carbonyl group restores carbonyl group
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iazomethane Diazomethane iazomethane CH Diazomethane, CH 2 N 2 – A potentially explosive, toxic, yellow gas; it is best presented as a hybrid of two contributing structures. represented as a hybrid of two contributing structures. + + HCN N : NN : C H : 1894 Von Pechmann a contemporary of Fischer H H In 1894 Von Pechmann, a contemporary of Fischer, reported that treating a carboxylic acid with diazomethane gives a methyl ester. + ether OO + Diazomethane A methyl ester CH 2 N 2 RCOH RCOCH 3 N 2
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iazomethane Diazomethane • Esterification occurs in two steps. Step 1: Proton transfer to diazomethane. + + + + RCOH O NN CH 2 O 3 N CO : RN A carboxylate anion Methyldiazonium cation Step 2: Nucleophilic displacement of N 2 . O O : RC H 3 + + S N 2 RO C H 3 CN N +
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cid Chlorides Acid Chlorides • The functional group of an acid halide is a carbonyl group bonded to a halogen atom. – Among the acid halides, acid chlorides are by far the most common and the most widely used. -C-X CH 3 CCl OO C-Cl O Functional group of an acid halide Acetyl chloride Benzoyl chloride
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cid Chlorides Acid Chlorides – Acid chlorides are most often prepared by treating a carboxylic acid with thionyl chloride. O O + + + OH SOCl 2 Cl SO 2 HCl Butanoic acid Thionyl chloride Butanoyl chloride
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cid Chlorides Acid Chlorides • The mechanism for this reaction is divided into two steps. Step 1: Reaction with SOCl 2 transforms OH, a poor leaving group, into a chlorosulfite group, a good aving group leaving group. O O O O A chlorosulfite group + + S Cl O C R R-C-O-H H-Cl Cl-S-Cl
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cid Halides Acid Halides Step 2: Attack of chloride ion gives a tetrahedral carbonyl addition intermediate, which collapses to ive the acid chloride give the acid chloride.
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This note was uploaded on 06/15/2009 for the course CH 53185 taught by Professor Sessler during the Spring '09 term at University of Texas at Austin.

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lecture 14 given - Lecture 14 Chemistry 310N Organic...

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