318-16 - Organic Lecture Series CH 318 N LECTURE 16...

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Organic Lecture Series 1 CH 318 N LECTURE 16 Textbook Assignment: Chapter 18 Homework (for credit): POW 7 posted (Due 3/22) Today’s Topics: Derivatives of Carboxylic Acids Notice & Announcements: Kyle Williams OH: 4-5 PM March 10 th and April 7 th Organic Lecture Series 2 Functional Functional Derivatives of Derivatives of Carboxylic Acids Carboxylic Acids acetaminophen
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Organic Lecture Series 3 Nucleophilic acyl substitution: Nucleophilic acyl substitution: an addition-elimination sequence resulting in substitution of one nucleophile for another Tetrahedral carbonyl addition intermediate - + + C Nu R C Y R C R O Y O O :Nu - :Y - Substitution product : Characteristic Reactions Characteristic Reactions Organic Lecture Series 4 in the general reaction, the leaving group, as an anion, illustrates an important point: the weaker the base, the better the leaving group R 2 N - RO - O RCO - X - Increasing basicity Increasing leaving ability Characteristic Reactions Characteristic Reactions
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Organic Lecture Series 5 Reaction with H Reaction with H 2 O O - Acid Chlorides Acid Chlorides –low-molecular-weight acid chlorides react rapidly with water –higher molecular-weight acid chlorides are less soluble in water and react less readily CH 3 CCl O H 2 OC H 3 COH O HCl + + Acetyl chloride Hydrolysis-bond breaking using water Organic Lecture Series 6 Reaction with H Reaction with H 2 O O - Anhydrides Anhydrides –low-molecular-weight acid anhydrides react readily with water to give two molecules of carboxylic acid –higher-molecular-weight acid anhydrides also react with water, but less readily 3 COCCH 3 OO H 2 H 3 O HOCCH 3 O + + Acetic anhydride
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Organic Lecture Series 7 Step 1: addition of H 2 O to give a TCAI O CH 3 -C-O-C-CH 3 H H O-H O O H H 3 -C-O-C-CH 3 H H O-H 3 -C-O-C-CH 3 O O H H H-O-H H + + + Tetrahedral carbonyl addition intermediate + O O O Organic Lecture Series 8 Step 2: protonation followed collapse of the TCAI O 3 -C-O-C-CH 3 O H O H H + O H H 3 C O O O C O 3 H H O H H + 3 CO O O CC H 3 O H H H H H + H + O
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Organic Lecture Series 9 Reaction with H Reaction with H 2 O O - Esters Esters • Esters are hydrolyzed only slowly, even in boiling water – hydrolysis becomes more rapid if they are heated with either aqueous acid or base • Hydrolysis in aqueous acid is the reverse of Fischer esterification – the role of the acid catalyst is to protonate the carbonyl oxygen and increase its electrophilic character toward attack by water (a weak nucleophile) to form a tetrahedral carbonyl addition intermediate – collapse of this intermediate gives the carboxylic acid and alcohol Organic Lecture Series 10 Acid Acid -catalyzed ester hydrolysis catalyzed ester hydrolysis R OCH 3 C O H 2 O H + OH C R 3 H + R C O CH 3 ++ Tetrahedral carbonyl addition intermediate Reaction with H Reaction with H 2 O O - Esters Esters
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Organic Chemistry Mechanism Worksheet 4 Acidic Conditions: H + Basic Conditions: OH -
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Organic Lecture Series 11 • Hydrolysis of an esters in aqueous base is often called saponification saponification
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318-16 - Organic Lecture Series CH 318 N LECTURE 16...

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