Chapter 18-2

Chapter 18-2 - CHEM 262 Wei You Chapter 18. Functional...

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1 CHEM 262 Wei You Chapter 18. Functional Derivatives of Carboxylic Acids (2)
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2 Characteristic Reactions 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 Nu R O Y O O :Nu - :Y - Substitution     product : Note: the weaker the base the better the leaving group. R 2 N - RO - O RCO - X - Increasing basicity Increasing leaving ability
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3 Characteristic Reactions halide ion is the weakest base and the best leaving group; acid halides are the most reactive toward nucleophilic acyl substitution amide ion is the strongest base and the poorest leaving group; amides are the least reactive toward nucleophilic acyl substitution
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4 Reversible
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5 Which one is leaving?
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6 General Mechanism (1). With a negatively charged nucleophile
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7 General Mechanism (2). With a neutral nucleophile
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8 General Mechanism (2’). Acid catalyzed
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9 Rxn with H 2 O - 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 O CH 3 COH O HCl + + Acetyl chloride
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10 Rxn with H 2 O - 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 CH 3 COCCH 3 O O H 2 O CH 3 COH O HOCCH 3 O + + Acetic anhydride
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Chapter 18-2 - CHEM 262 Wei You Chapter 18. Functional...

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