carboxylic acid derivatives nucleophilic acyl substitution
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Carboxylic Acid Derivatives: Nucleophilic Acyl Substitution

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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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reading assignment
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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organic nomenclature assignment
Organic Nomenclature Assignment
  • Esters
  • Amides

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

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the acyl group
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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the esters
The Esters

Every ester consists of two components, the acyl part and the alkylpart.

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naming the esters
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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nomenclature of the esters
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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slide9
Ethyl pentanoate

Ethyl valerate

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slide10
Methyl 2-methylpropanoate

Methyl a-methylpropionate

Methyl isobutyrate

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slide11
Isopropyl benzoate

Isopropyl benzenecarboxylate

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slide12
tert-Butyl phenylethanoate

tert-Butyl phenylacetate

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nomeclature of the amides
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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slide15

Butanamide

Butyramide

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slide16

4-Methylbenzenecarboxamide

4-Methylbenzamide (acceptable IUPAC alternative name)

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slide18

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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functional group interconversions
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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functional group interconversions1
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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nucleophilic acyl substitution
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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energy profile for nucleophilic acyl substitution
Energy Profile for Nucleophilic Acyl Substitution

Intermediate

Energy

Reactants

Products

Reaction Coordinate

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slide26

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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nucleophilic substitution acid catalyzed mechanism
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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slide29

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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