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Chemistry  2030      “Introduction  to  Organic  Chemistry”      

Fall  Semester  2012      Dr.  Rainer  Glaser      

Examination #4

“Carbonyl Compounds and Amines.”

Thursday, November 15, 2012, 8:25 – 9:15 am

Name:

Answer Key

Question 1. Aldehydes and Ketones 20 Question 2. Carboxylic Acids and Anhydrides 20 Question 3. Carboxylic Acid Esters 20 Question 4. Carboxylic Acid Halides, Anhydrides and Amides 20 Question 5. Amines and Diazonium Ions 20

Total 100

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Question 1. Aldehydes and Ketones. (20 points) (a) Acetophenone (H5C6−CO−CH3) is an enolizable ketone. Draw the two important resonance forms of the anion formed by deprotonation of acetophenone. Show all lone pairs and formal charges; use the correct resonance arrow. Use curved arrows to show the electron flow that converts one resonance forms into the other. (6 points)

(b) Draw the structural formula and provide the name of one non-enolizable carbonyl (aldehyde or ketone) of your choice. (4 points)

Show formaldehyde,

or benzaldehyde, or benzophenone…

(c) The compound shown, but-2-enal, can be prepared in two steps beginning with acetaldehyde. The first reaction is a base-catalyzed aldol reaction and the second reaction is the thermal elimination of ___WATER__. Provide a structural formula of the aldol. In the structures of both the aldol and the but-2-enal, circle the fragment that functioned as the enolate in the aldol reaction. (5 points)

Acetaldehyde Aldol

(d) Cinnamaldehyde (H5C6−CH=CH−CHO) can be prepared in a two-step sequence consisting of an aldol reaction and thermal condensation. This synthesis involved a __MIXED_ aldol reaction between the non-enolizable aldehyde _benzaldehyde_ and the enolizable aldehyde _acetaldehyde_. (5 points)

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Question 2. Carboxylic Acids and Anhydrides. (20 points) (a) Carboxylic acids and carboxylic acid amides form strongly bonded dimeric aggregates either with themselves (homodimer) or with each other (heterodimer). The electrostatic potential surface plots are shown of the homodimer of propanoic acid, H3C−CH2−COOH, and of the heterodimer of propanoic acid and its amide, H3C−CH2−CONH2. Decide which plot shows which dimer and draw the complete structural formula of each dimer in the space above the plot. Indicate H-bonds as dashed lines. (6 points)

(b) Syntheses of carboxylic acids. Provide substrate, reagent or product as requested. (12 points)

Product formed by oxidation of toluene, C6H5−CH3 with hot KMnO4:

C6H5−COOH

Product formed by oxidation of p-xylene, H3C−C6H5−CH3 with hot KMnO4:

Reagent that reacts with phenylmagnesium bromide, H5C6MgBr to form benzoic acid,

H5C6−COOH after workup with dilute acid:

O=C=O

Product of the acid-catalyzed hydrolysis of malononitrile, :N≡C−CH2−C≡N:

HOOC−CH2−COOH

(c) Succinic acid is the trivial name of butanedioic acid (note “butane”). Succinic anhydride is the intramolecular anhydride of succinic acid. Draw the structure of succinic anhydride in the box to the right. (2 points)

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Question 3. Carboxylic Acid Esters. (20 points) (a) Methyl formate H−CO−O−CH3 can be made by Fischer esterification of the carboxylic acid ______________ (formic acid, acetic acid, benzoic acid) and the alcohol __________ (methanol, ethanol, phenol). “Fischer esterification” means that the ester formation is catalyzed by a strong mineral acid. (2 points) (b) Consider the mechanism of the formation of methyl formate H−CO−O−CH3 by Fischer esterification. Draw the structural formulas of the species indicated. Draw all lone pairs, provide all formal charges. You may abbreviate the methyl group as “H3C−” or as “Me−”. (12 points)

1: Protonated carboxylic acid, i.e., the actual substrate for alcohol addition

2: Product formed by addition of alcohol to the protonated carboxylic acid

3: Neutral gem tri-functional intermediate

4: Protonated gem tri-functional intermediate that will lead to water elimination

(c) Consider the reaction of methyl formate with dimethylamine. Provide the structural formulas of all the products formed in the reaction and provide an acceptable name for the amide. (6 points)

N,N-dimethylformamide

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Question 4. Carboxylic Acid Halides, Anhydrides and Amides. (20 points) (a) Consider the preparation of acetyl chloride from acetic acid using phosphorus pentachloride. Draw structural formulas of the substrate, of the reagent, of the organic product (the acetyl chloride), and also of the inorganic products. (8 points)

(b) Consider the formation of N,N-dimethylacetamide, H3C−CO−N(CH3)2 by reaction of acetic anhydride with dimethylamine. Two molecules of the amine are required for every molecule of acetic anhydride used. Show reaction equations for the reaction A of the first amine with the anhydride and for the reaction B of the second amine with the _ACETIC ACID_ formed in the preceding reaction. (8 pts)

(c) Draw the structures of the products of hydrolysis of N,N-dimethylacetamide, H3C−CO−N(CH3)2 in the presence of NaOH. [Hint: Account for salt formation.] (4 points)

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Question 5. Amines and Diazonium Ions. (20 points) (a) Consider the reaction of trimethylamine, N(CH3)3 with benzyl iodide, H5C6−CH2−I. Draw the structure of the product and provide its name. (4 points)

benzyltrimethylammonium iodide

(b) Devise a synthesis of N,N-diethyl-m-toluamide (the insect repellent OFFTM) by reaction of the appropriate amine, __diethylamine__ (name of the amine), and m-toluyl chloride in the presence of NaOH. Draw the structures of the amine, of the acid chloride, of the amide product, and of the inorganic products. (10 points)

(c) Complete this scheme by providing the structure of the intermediate (center box) and the two reagents (boxes over arrows). (6 points)