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Carboxylic Acid Derivatives: Nucleophilic Acyl Substitution

Carboxylic Acid Derivatives: Nucleophilic Acyl Substitution. Chapter 19. Reading Assignment. DO: Sections 19.0 - 19.1, 19.4, 19.5, 19.7 - 19.15, 19.17 - 19.20, 19.22 - 19.24, 19.35 Problems READ WITHOUT LECTURE: Sections 19.16, 19.26 - 19.34 SKIP: Sections 19.2 - 19.3, 19.6, 19.21, 19.25.

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Carboxylic Acid Derivatives: Nucleophilic Acyl Substitution

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  1. Carboxylic Acid Derivatives:Nucleophilic Acyl Substitution Chapter 19 WWU-Chemistry

  2. Reading Assignment • DO: • Sections 19.0 - 19.1, 19.4, 19.5, 19.7 - 19.15, 19.17 - 19.20, 19.22 - 19.24, 19.35 • Problems • READ WITHOUT LECTURE: • Sections 19.16, 19.26 - 19.34 • SKIP: • Sections 19.2 - 19.3, 19.6, 19.21, 19.25 WWU-Chemistry

  3. Organic Nomenclature Assignment • Esters • Amides WWU-Chemistry

  4. Problem Assignment • In-Text: • 19-4 - 19-7, 19-9 - 19-27, 19-31 - 19-40 • End-of-Chapter: • 1 - 3 (parts) • 4 - 21 WWU-Chemistry

  5. The Acyl Group All carboxylic acid derivatives contain an acyl group. The substituent attached to the acyl group determines the class of carboxylic acid derivative. WWU-Chemistry

  6. The Esters Every ester consists of two components, the acyl part and the alkylpart. WWU-Chemistry

  7. Naming the Esters • Esters may be treated as if they were the product of the reaction of a carboxylic acid and an alcohol. • Thus their names derive from the names of the carboxylic acid and the alcohol. WWU-Chemistry

  8. Nomenclature of the Esters • IUPAC • Change carboxylic acid ending from “-oic acid” to “-oate” • Add name of alkyl group • Form: • Alkyl alkanoate • Common • Same as above: change “-ic acid” to “-ate” and add alkyl group name. WWU-Chemistry

  9. Ethyl pentanoate Ethyl valerate WWU-Chemistry

  10. Methyl 2-methylpropanoate Methyl a-methylpropionate Methyl isobutyrate WWU-Chemistry

  11. Isopropyl benzoate Isopropyl benzenecarboxylate WWU-Chemistry

  12. tert-Butyl phenylethanoate tert-Butyl phenylacetate WWU-Chemistry

  13. Methylcyclohexanecarboxylate WWU-Chemistry

  14. Nomeclature of the Amides • IUPAC • Change carboxylic acid ending from “-oic acid” to “-amide”. • Form: • Alkanamide • Common • Same as above: change “-ic acid” to “-amide”. WWU-Chemistry

  15. Butanamide Butyramide WWU-Chemistry

  16. 4-Methylbenzenecarboxamide 4-Methylbenzamide (acceptable IUPAC alternative name) WWU-Chemistry

  17. Cycloheptanecarboxamide WWU-Chemistry

  18. A well-known characteristic of the esters is that they are the substances responsible for the characteristic flavors and fragrances of fruits and flowers. On the next image, you will see a partial list of esters and their characteristic flavors and fragrances. WWU-Chemistry

  19. Esters as Flavoring Substances WWU-Chemistry

  20. Carboxylic Acid Derivatives WWU-Chemistry

  21. Functional Group Interconversions • The next image outlines interconversions that can be made among the carboxylic acid derivatives. • The purpose of the image is to illustrate that all of the carboxylic acid derivatives are inter-related and that all can, in principle, be converted into one another. • Note the central location of the acid chlorides. All conversions from carboxylic acids to derivatives are best conducted through the corresponding acid chloride. WWU-Chemistry

  22. Functional Group Interconversions H2O OH- R’OH H2O H2O SOCl2 R’OH OH- NH3 NR’2H NH3 NR’2H RCOOH H2O RCOOH NH3 NR’2H NH3 NR’2H WWU-Chemistry

  23. Nucleophilic Acyl Substitution • All of the interconversions among carboxylic acids and their derivatives take place following one general mechanism • This mechanism is nucleophilic acyl substitution. • For each case, the only significant differences lies in the nature of the leaving group and the nucleophile. WWU-Chemistry

  24. Nucleophilic Acyl Substitution WWU-Chemistry

  25. Energy Profile for Nucleophilic Acyl Substitution Intermediate Energy Reactants Products Reaction Coordinate WWU-Chemistry

  26. This intermediate can collapse either by loss of the Y group (leads to a forward reaction) of by the loss of the Nu group (leads to a reverse reaction). Either pathway can take place, as this is a reversible process. WWU-Chemistry

  27. Nucleophilic Substitution(Acid-catalyzed Mechanism) • When the nucleophile is relatively weak (e.g., water, alcohols), an acid-catalyzed mechanism is preferred. • The role of the acid is to protonate the acyl oxygen, thus increasing the positive charge character on the acyl carbon (through resonance). • This makes the acyl carbon a better site for nucleophilic attack. WWU-Chemistry

  28. Nucleophilic Acyl Substitution(Acid-Catalyzed) WWU-Chemistry

  29. This intermediate can collapse either by loss of the Y group (leads to a forward reaction) of by the loss of the Nu group (leads to a reverse reaction). Either pathway can take place, as this is a reversible process. WWU-Chemistry

  30. The nucleophile (Nu) can be any of the following: WWU-Chemistry

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