1. Carboxylic Acid Derivatives: Nucleophilic Acyl Substitution
Chapter 19
Carboxylic Acid Derivatives: Nucleophilic Acyl Substitution
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2. Reading Assignment DO: READ WITHOUT LECTURE: SKIP:
Sections , 19.4, 19.5, , , , 19.35
Problems
READ WITHOUT LECTURE:
Sections 19.16,
SKIP:
Sections , 19.6, 19.21, 19.25
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3. Organic Nomenclature Assignment
Esters
Amides
Make this assignment
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4. Problem Assignment In-Text: End-of-Chapter:
, ,
End-of-Chapter:
1 - 3 (parts)
4 - 21
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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.
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6. The Esters
Every ester consists of two components, the acyl part and the alkyl part.
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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.
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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.
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9. Ethyl pentanoate
Ethyl valerate
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10. Methyl 2-methylpropanoate Methyl a-methylpropionate Methyl isobutyrate
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11. Isopropyl benzenecarboxylate
Isopropyl benzoate
Isopropyl benzenecarboxylate
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12. tert-Butyl phenylethanoate tert-Butyl phenylacetate
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13. Methyl cyclohexanecarboxylate
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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”.
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15. Butanamide
Butyramide
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16. 4-Methylbenzamide (acceptable IUPAC alternative name)
4-Methylbenzenecarboxamide
4-Methylbenzamide (acceptable IUPAC alternative name)
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17. Cycloheptanecarboxamide
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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.
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19. Esters as Flavoring Substances
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20. Carboxylic Acid Derivatives
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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.
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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
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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.
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24. Nucleophilic Acyl Substitution
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25. Energy Profile for Nucleophilic Acyl Substitution
Intermediate
Energy
Reactants
Products
Reaction Coordinate
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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.
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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.
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28. Nucleophilic Acyl Substitution (Acid-Catalyzed)
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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.
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30. The nucleophile (Nu) can be any of the following:
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