Chemistry 2030, FS17, Dr. Rainer Glaser Introduction to Organic Chemistry Examination #4 Aldehydes & Ketones, Carboxylic Acids & Carboxylic Acid Derivatives, Lipids & Detergents, and Amines. Handout: Tuesday, December 5, 2017, end of class. Return: Wednesday, December 6, 2017, by 2 pm, to Instructor, TA or Dept. Chem. Office Staff. Name: Answer Key Question 1. Aldehyde and Ketones 20 Question 2. Carboxylic Acids and Derivatives 30 Question 3. Lipids and Detergents 15 Question 4. Amines and Ammonium Ions 20 Question 5. Diazonium Ions and Azo Compounds 15 Total 100 ALLOWED: Books, notes, whatever other materials. Collaboration with your peers in class is encouraged. Do NOT consult anybody outside of the group of your Chem 2030 peers! You must submit your own work in your own writing, and you will be graded on your submission. 1
Question 1. Aldehydes & Ketones. (20 points) (a) Consider the reaction of propanal with ethylmagnesium bromide. Provide the structures of propanal, of the initial addition product (an alkoxide), and of the product formed after hydrolysis. This reaction exemplifies the general approach for the synthesis of a (primary, secondary, tertiary) alcohol by reaction of an aldehyde with a Grignard reagent and subsequent hydrolysis. (4 pts.) (b) Draw the structures of the products formed by the reaction of benzophenone, (C 6 H 5 ) 2 C=O with the indicated reagents. In each case, write down the name of the class of compounds to which the product belongs. The box on the left serves as an example. (4 points) Rxn w/ H 2 N CH 3 Rxn w/ HO CH 2 CH 3 Rxn w/ HO CH 2 CH 2 OH (C 6 H 5 ) 2 C=N CH 3 an imine hemiacetal acetal (c) Draw the two main resonance forms of the enolate formed by deprotonation of cyclohexanone at the (α, β, γ) carbon. 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) (d) On the left, draw the structure of the product of the base-catalyzed aldol reaction of cyclohexanone. On the right, draw the structure of the dehydration product of the initially formed product. (6 points) Product of Aldol Reaction Dehydration Product 2
Question 2. Carboxylic Acids and Derivatives. (30 points) (a) The electrostatic potential (ESP) surface plot is shown of benzoic acid, H5C6-COOH. Draw the complete structure of benzoic acid. Your structure drawing should be aligned as much as possible with the orientation of the molecules in the ESP plot. In your structure drawing, draw a SQUARE around the hydrogen bond donor and draw a CIRCLE around the best hydrogen bond acceptor. Provide a drawing of the H-bonded dimer formed by two benzoic acid molecules. (6 points) Benzoic Acid Benzoic Acid Dimer (b) Ethyl acetate H3C CO O CH2 CH3 can be made by Fischer esterification of acetic acid and ethanol. Consider the mechanism of ethyl acetate formation by Fischer esterification (catalyzed by a strong mineral acid). Draw the structural formulas of the species indicated (show all lone pairs and formal charges). You may abbreviate the methyl group as H3C or as Me and the ethyl group as H5C2 or as Et. (8 points) 1: Protonated carboxylic acid, i.e., the actual 2: Product formed by addition of alcohol substrate for alcohol addition to the protonated carboxylic acid 3: Neutral gem tri-functional intermediate 4: Protonated gem tri-functional intermediate that will lead to water elimination 3
(c) Nepetalactone is the active ingredient in catnip. Consider the hydrolysis of this lactone. Draw the structure of the initially formed product in the center. The initially formed product is unstable and will undergo to form a more stable isomer. Draw the final product on the right. (5 pts.) Nepetalactone Initial Product of Hydrolysis Final Product of Hydrolysis (d) The reaction of nepetalactone with anhydrous ammonia leads to the formation of nepetalactam. Suggest a reasonable mechanism for this reaction and show the likely intermediates. (6 points) reasonable alternatives receive credit as well (e) Synthesis of propionic acid from alkyl bromide. Show the reaction intermediates and provide the reagents (1) for the Grignard formation, (2) for the reaction of the Grignard compound, and (3) for the workup that gives the neutral carboxylic acid. (5 points) 4
Question 3. Lipids and Detergents. (15 points) (a) Draw the structure of the fat glyceryl palmito-stearo-linoleate. Clearly show the stereochemistry of any double bond(s). (5 points) any sequence of the fatty acids received credit (b) Classic soaps have been largely replaced by alkylbenzenesulfonate detergents. Draw the structure of sodium decylbenzenesulfonate. Circle the polar region of the detergent molecule. Draw a square around the nonpolar region of the detergent molecule. (4 points) square around decyl group (and benzene); circle around sulfonate (and part of benzene) (c) A liposome is shown schematically; a liposome is a spherical vesicle formed by a lipid bilayer. Liposomes often are formed by phosphatidylcholine. (i) Draw the structure of dipalmitoylphosphatidylcholine and explain which parts of the molecule correspond to the blue circle and the wiggly lines in the scheme. (ii) Liposomes can be used for drug delivery. Suppose you want to deliver a hydrophobic drug. Where would this hydrophobic drug be stored in the liposome? You can draw a cartoon of a liposome loaded with a hydrophobic drug. (6 points) 5
Question 4. Amines and Ammonium Ions. (20 points) (a) For each of the two amine syntheses, draw the structures of the substrates X and Y. (4 points) Synthesis of aniline Synthesis of H 3 C CH 2 NH 2 by reduction of X with SnCl 2 /HCl: by reduction of Y with NaBH 3 CN: Nitrobenzene H 3 C CH=NH (b) Properties of Amines. True or False? (5 points) True False Boiling point of H 3 C NH 2 is higher than the boiling point of H 3 C CH 3. YES N,N-methylethylammonia contains an sp 3 -N. YES N,N-methylethylammonia is chiral. NO It is easier to protonate aniline than para-chloroaniline. YES It is easier to protonate ethylamine than acetamide. YES (c) Consider the two-step reaction of methylamine to dimethylamine. Show reaction equations for both steps. (6 points) H 3 C NH 2 + H 3 C Cl --> (CH 3 ) 2 NH 2 + Cl - (CH 3 ) 2 NH 2 + Cl - + Na + OH - --> (CH 3 ) 2 NH + Cl - + Na + + H 2 O (d) Consider the reaction of trimethylammonium chloride, [(CH 3 ) 3 NH] + Cl - with ethylene oxide to form choline, a.k.a. (2-hydroxyethyl)trimethylammonium chloride. Show the mechanism of this reaction, i.e., show all intermediates on the reaction path. (5 points) 6
Question 5. Diazonium Ions and Azo Compounds. (15 points) (a) Resonance forms of benzenediazonium ion, H 5 C 6 N 2 +. Draw one resonance form that carries the formal charge at Nα and draw another resonance form that carries the formal charge at Nβ. (3 points) (b) Benzenediazonium salts are useful in synthesis because they can be employed as substrates to prepare substituted benzenes by way of nucleophilic aromatic substitution. Show substrate, reagents and catalysts (if any) to convert meta-bromoaniline into meta-bromochlorobenzene in two steps. (4 pts.) (c) In the synthesis of an azo dye a benzenediazonium ion is employed as reagent in an electrophilic aromatic substitution. Draw the complete structure of the sigma-complex formed when the benzenediazonium ion formed by diazotization of para-nitroaniline attacks the para-position of N,Ndimethylaniline, H 5 C 6 N(CH 3 ) 2. Also draw the structure of the azo dye formed after completion of the electrophilic aromatic substitution. (8 points) Sigma complex formed by reaction of p-o 2 N H 4 C 6 N 2 + and H 5 C 6 N(CH 3 ) 2 Azo dye formed by reaction of p-o 2 N H 4 C 6 N 2 + Cl - and H 5 C 6 N(CH 3 ) 2 7