PRACTICE EXERCISES FOR CHAPTER 16
1. Write the structures of the following carboxylic acids: formic, benzoic, and 2-hydroxypropanoic acids.
2.Write three resonance structures for a carboxylic acid. Which one is the lowest energy structure? Which is the highest energy structure? Why? What kind of character is present on the carbonyl carbon? What effect does the hydroxyl function have on this character and how does it do this (what kind of effect and what aspect of the oxygen provides the effect)?
3. What effect does the resonance stabilization of a carboxylic acid have on the acidity of the hydroxyl protons, if considered by itself? Briefly explain with the help of an energy diagram. What is the approximate pKa of a simple carboxylic acid? Of an alcohol? By what factor is the carboxylic acid more acidic? Rigorously xplain the enhanced acidity, taking into account among other things, the substantial resonance stabilization of the carboxylic acid itself.
4. 2-chloroacetic acid is significantly more acidic than acetic acid. Explain in terms of a specific type of substituent effect upon a specific species in the equilibration for acid catalyzed dissociation in water. Also, provide a pictorial illustration of the effect.
5.Explain why the reduction of carboxylic acids with lithium aluminum hydride is rather slow in comparison to the reduction of ketones and aldehydes and even in comparison to esters.Provide two unrelated reasons.
6 What is the oxidation number of the carbonyl carbon of a ketone and of a carboxylic acid? What about the carbon of an alcohol which is directly attached to the OH group? In what molecule does carbon have an oxidation number of +4?
7.Write the detailed (two step) mechanism for the reduction of a carboxylic acid with borane and explain in detail why the carboxyl group is more reactive than a ketone function.
8.Write three resonance structures for the conjugate acid of a carboxylic acid. Explain why protonation occurs selectively upon the carbonyl oxygen rather than upon the hydroxyl function.
9.Write the detailed mechanism of acid catalyzed esterification. Describe the position of the equilibrium and explain why this is plausible. Indicate two methods by which the equilibrium can be forced to the product (ester) side.
10. Sketch equations which show an alternative, indirect method for the synthesis of esters from carboxylic acids.
11.Sketch equations for two different methods for the synthesis of carboxylic acids, one of which involves the use of a Grignard reagent.
12.Explain , using equations to assist your explanation, why neither base catalyzed or base promoted esterification is successful.
13. What is the reaction type in the conversion of a carboxylic acid to an ester (provide both the reaction type and the mechanistic type). How can the indirect mechanism for this reaction be described as a combination of fundamental reaction types.