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Organic Chemistry 6 th Edition Paula Yurkanis Bruice. Chapter 17 Carbonyl Compounds I Reactions of Carboxylic Acids and Carboxylic Acid Derivatives. Class I Carbonyl Compounds. Class II Carbonyl Compounds. Nomenclature of Carboxylic Acids.
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Organic Chemistry 6th Edition Paula Yurkanis Bruice Chapter 17 Carbonyl Compounds I Reactions of Carboxylic Acids and Carboxylic Acid Derivatives
In systematic nomenclature, the carbonyl carbon is always C-1 In common nomenclature, the carbon next to the carbonyl is the a-carbon
The functional group of a carboxylic acid is called a carboxyl group
Acyl Halides Acid Anhydrides
Amides If a substituent is bonded to the nitrogen, the name of the substituent is stated first:
Two major resonance contributors in esters, carboxylic acids, and amides:
Carboxylic acids have relatively high boiling points because… Amides have the highest boiling points:
Naturally Occurring Carboxylic Acids and Carboxylic Acid Derivatives
The reactivity of carbonyl compounds resides in the polarity of the carbonyl group:
The tetrahedral intermediate is a transient species that eliminates the leaving group Y– or the nucleophile Z–: This is a nucleophilic acyl substitution reaction
Z– will be expelled if it is a much weaker base than Y–; that is, Z– is a better leaving group than Y– (k–1 >> k2):
Y– will be expelled if it is a weaker base than Z–; that is, Y– is a better leaving group than Z– (k2 >> k–1):
Both reactant and product will be present if Y– and Z– have similar leaving abilities:
Reaction Coordinate Diagrams for Nucleophilic Acyl Substitution Reactions (a) the Nu– is a weaker base (b) the Nu– is a stronger base (c) the Nu– and the leaving group have similar basicities
The reactivity of a carboxylic acid derivative depends on the basicity of the substituent attached to the acyl group:
Electron withdrawal increases the carbonyl carbon’s susceptibility to nucleophilic attack: The weaker the basicity of Y, the greater the reactivity:
Weak bases are easier to expel when the tetrahedral intermediate collapses:
A carboxylic acid derivative can be converted only into a less reactive carboxylic acid derivative:
A base is required to trap the HCl product Reactions of Acyl Halides Suitable bases include triethylamine (TEA) and pyridine
TEA Excess amine traps HCl
Formation of Amides from Acyl Halides Tertiary amines cannot form amides
Reactions of Acid Anhydrides Acid anhydrides do not react with sodium chloride or with sodium bromide because Cl– and Br– are weaker bases than acetate
Mechanism for the conversion of an acid anhydride into an ester (and a carboxylic acid): Elimination facilitated by protonation Addition facilitated by protonation In the absence of an acid catalyst, the reaction is sluggish, but the reaction speeds up as acid products are formed
Phenyl esters are more reactive than alkyl esters because phenolate ions are weaker bases than alkoxide ions:
Hydrolysis of an ester with primary or secondary alkyl groups can be catalyzed by an acid The carbonyl oxygen is first protonated, Because…
Excess water will force the equilibrium to the right Alcohols that have low boiling points can be removed by distillation as they are formed