CEM 203 Final Exam December 15, 2010 Your name: ANSWERS This a closed-notes, closed-book exam You may use your set of molecular models This test contains 15 pages Time: 2h 30 min 1. / 16 2. / 15 3. / 24 4. / 35 5. / 36 6. / 36 7. / 40 8. / 48 TTAL / 250 = / 100 This exam counts for 45% of your CEM 203 final grade
Chem 203 final exam p. 2 of 15 1. (16 pts.) Indicate the approximate pka's for the Bronsted dissociation of the proton in boldface in the following molecules (write your answers in the appropriate boxes) C N Br 50 3 35 8 C 3 C C S 2 CF 3 C 3 C 2 25 10 40 17 2. (15 pts.) Write a detailed mechanism to account for the observation that treatment of compound A with ozone, but without the usual Zn/ + step, furnishes a 1 : 1 mixture of products B and C: 3 no Zn / + + A B C 1 : 1 ratio + ± + ± + B C
Chem 203 final exam p. 3 of 15 3. (24 pts.) Draw: a. Accurate mechanisms for an example of S N 2 reaction and an example of S N 1 reaction: S N 2: Br N 3 + Br N 3 S N 1: Cl C 3 (or other C 3 Cl C 3 ± + C 3 polar solvent) b. A chemical equation showing an example of Williamson reaction (without mechanism): Na C 3 I C 3 c. A chemical equation showing an example of Wittig reaction (without mechanism): Ph 3 P=C 2
Chem 203 final exam p. 4 of 15 d. A chiral Schiff base: N e. An achiral epoxide that will react with aq. 2 S 4 to form a chiral diol: f. An olefin containing at least than 3 C atoms that will produce the same diol when treated either with s 4 followed by aq. NaS 3, or with MCPBA followed by aq. 2 S 4. g. An alcohol containing at least 4 C atoms that is likely to undergo dehydration without rearrangement and one also containing at least 4 C atoms that is likely to undergo rearrangement during dehydration (write your answers in the appropriate boxes): not likely to rearrange likely to rearrange h. An alcohol that forms the same product when treated either with PCC or with the Jones reagent, and one that forms one product when treated with PCC, but a different product when treated with the Jones reagent (write your answers in the appropriate boxes): gives the same product gives two different products
Chem 203 final exam p. 5 of 15 4. (35 pts.) The 1 NMR spectrum of an alkane, A, exhibited only a singlet at 0.9 ppm. Treatment of A with Cl 2 / hv afforded a monochloro derivative, B, which upon reaction with metallic Mg followed by formaldehyde, -C, produced compound C. The IR spectrum of C displayed a strong, broad absorption at 3340 cm 1. The 1 NMR spectrum of C is shown below. Reaction of C with 2 S 4 at 160 C yielded compound D. When substance D was treated with s 4 followed by aqueous NaS 3, compound E emerged. Furthermore, ozonolysis of D followed by Zn/ + produced only F, which upon treatment with NaB 4 furnished G. The 1 NMR spectra of E and G are also provided below. Deduce the structures of compounds A G and write your answers in the appropriate boxes. s 4, then E A Cl 2 hv B 1. Mg 2. C C 2 S 4 160 C D aq. NaS 3 3, then F Zn, + NaB 4 G Compound A Compound B Compound C Cl Compound D Compound E Compound F Compound G
Chem 203 final exam p. 6 of 15 9 2 1 2 1 NMR spectrum of A 1 NMR spectrum of C 3427 IR spectrum of E 1 NMR spectrum of E
Chem 203 final exam p. 7 of 15 1715 IR spectrum of F 1 NMR spectrum of F 6 1 1 3345 IR spectrum of G 1 NMR spectrum of G
Chem 203 final exam p. 8 of 15 5. (36 pts.) Indicate which among compounds a-j produce the spectra shown below: Br a b c d e C CN f g h i j these are the spectra of compound: j 1745 1723 ppm 2266 these are the spectra of compound: f 1749 ppm
Chem 203 final exam p. 9 of 15 these are the spectra of compound: c 1694 ppm these are the spectra of compound: h 1736 ppm
Chem 203 final exam p. 10 of 15 6. (36 pts.) Draw the structure of the major product expected from each of the following reactions. If no overall change is predicted, answer "N REACTIN." Important: where appropriate, molecules must be drawn with the correct configuration a. 1. Br, rad. init. 2. C 3 C C Na then mild 3 + 3. Na. N 3(liq) N REACTIN b. 1. 2 S 4, heat 2. 3, then Zn / + 3. NaB 4, then mild 3 + c. 1. s 4, then aq. NaS 3 2. acetone, cat. 2 S 4, 60 C, removal of 2 (or enantiomer) 1. B 3, then 2 2, aq. Na d. 2. PCC 3. C C Na then mild 3 + 1. NBS, rad. initiator e. 2. Mg 3. -C, then mild 3 + f. Ts 1. 2. MCPBA K 3. C 3 MgBr, CuBr, then mild 3 + (or enantiomer)
Chem 203 final exam p. 11 of 15 7. (40 pts.) Indicate all the reagents, catalysts, etc., in the correct order, that are necessary to induce the transformations shown below. List such reagents above / below the reaction arrows. If a product does not appear to be available from the substrate shown by any method known to you, write "INACCESSIBLE" on the reaction arrow. 1. Cl 2, hv a. 2. K 3. 3, then 2 2, + b. 1. 2, Lindlar [or Na / N 3(liq) ] 2. 2, 2 S 4 (or hydroboration) 3. PCC (or Jones) c. 1. 2 S 4, heat 2. B 3, then 2 2, aq. Na d. 1. 2, Lindlar [or Na / N 3(liq) ] 2. PCC 3. C 3 MgBr 4. PBr 3 5. B 3, then 2 2, aq. Na 6. Na (other anwers possible) e. 1. PBr 3 N 3 2. NaN 3 f. 1. TsCl, pyridine N 3 2. NaN 3 g. 1. B 3, then 2 2, aq. Na 2. PCC h. C 3 1. LiAl 4 2. PCC 3. Ph 3 P=C 2
Chem 203 final exam p. 12 of 15 8. (48 pts.) Propose a good synthesis of the molecules shown below using only methanol, NaCN, acetylene and ethylene oxide (see below) as the sources of carbon atoms. Intermediates / products obtained during an earlier sequence may be employed in a subsequent procedure, without showing their preparation again. Assume the availability of all necessary reagents (such as bases, acids, B 3, Mg, TsCl, PCC, PBr 3, MCPBA, etc.). C 3 C C 2 C C 2 methanol acetylene ethylene oxide Important: Note: answers other than the ones given below are possible i. aqueous workups at the end of each reaction are understood and need not to be shown. ii. It is not necessary to write mechanisms a. 2 Lindlar Na C C C 3 + Jones C C C 3 NaN 2 -I C C Na C 3 I NaN 2 C C C 3 2 Lindlar 2 S 4 2 b. N 2 (e.g. MgS 4 ) + 2 N (part a.) 1. B 3 2. 2 2 aq. Na PCC PBr 3 Br 1. NaN 3 2. Zn, +
Chem 203 final exam p. 13 of 15 c. C 3 C C Na (part a.) PCC C 3 1. B 3 2. 2 2 aq. Na 2 Lindlar C 3 Na C 3 I (part a.) d. C 3 cat. 2 S 4 heat, 2 (part a.) + C 3 1.s 4 2. aq. NaS 3 C 3 (part c.)
Chem 203 final exam p. 14 of 15 e. C Jones Na N 3 (liq) 1. NaN 2 2. (part a.) -I I + C C Na (part a.) f. Jones + BrMg PCC Mg (part c.) 2 Pd Br (part b.)
Chem 203 final exam p. 15 of 15 Characteristic Infrared Absorptions of Common Functional Groups Functional Group Bond Frequency Range (cm 1 ) Functional Group Bond Frequency Range (cm 1 ) Alcohol 3400 3650 (s, broad) Nitrile 2210 2260 (w m) C N C 1050 1150 (s) Carboxylic acid 2500-3100 (s, broad) Ether C 1000 1260 C= 1700 1720 (s) Amine N 3300 3350 (m) Ester C= 1710 1750 (s) Alkane C 2850 2950 (m s) Acyl halide C= 1770 1820 (s) Alkene =C 3020 3100 (m) Acid anhydride C= 1740 1790 (s) C=C 1640 1680 (m) 1800 1850 (s) Alkyne C C C 3270 3330 (s) Amide C= 1630 1700 (s) 2100 2260 (w m) Aldehyde, ketone C= 1680 1730 (s) Characteristic Proton ( 1 ) NMR Chemical Shifts Type of ydrogen Structure Chemical Shift δ (ppm) Reference (C 3) 4Si 0.00 Amines Type of ydrogen Structure N C Chemical Shift δ (ppm) 2.3 3.0 Alkane, primary -C 3 0.7 1.3 Alcohol, ether C 3.3 4.0 Alkane, secondary -C 2-1.2 1.4 Ester 3.7 4.8 C C Alkane, tertiary C 1.4 1.7 lefinic C=C- 5.0 6.5 Allylic, primary C=C-C 3 1.6 1.9 Aromatic Ar 6.5 8.0 Methyl carbonyl 2.1 2.5 Aldehyde 9.7 10.0 C C 3 C Aromatic methyl Ar C 3 2.5 2.7 Amine N 2 1 5, variable Alkyne C 2.5 2.7 Alcohol 1 5, variable Alkyl halide 2.5 4.5 Carboxylic acid C 11.0 12.0 (X = Cl, Br, I) C X