CEM 203 Midterm Exam 1 ctober 31, 2008 Your name: ANSWERS This a closed-notes, closed-book exam You may use your set of molecular models This exam contains 8 pages Time: 1h 30 min 1. / 15 2. / 16 3. / 11 4. / 18 5. / 20 6. / 20 TTAL / 100 This exam counts for 15% of your CEM 203 final grade
Chem 203 midterm exam 1 p. 2 of 8 1. (15 pts.) Write accurate structures of: 1. An alkene containing at least 7 C atoms that is likely to undergo rearrangement upon reaction with, and an alkene also containing at least 7 C atoms that is not likely to undergo rearrangement under the same conditions (write your answers in the appropriate boxes): likely to undergo rearrangement NT likely to undergo rearrangement many other answers are possible many other answers are possible 2. An achiral alkene that produces a chiral diol upon reaction with s 4 followed by aq. NaS 3 solution, as well as a chiral dichloride upon reaction with 2 : (many other answers are possible) 3. An achiral alkene that produces a chiral alcohol upon reaction with B 3 followed by aq. Na and 2 2, but an achiral alcohol upon reaction with 2 S 4 and 2 : (many other answers are possible) 4. An alkene that contains at least 6 C atoms, and that produces the same alcohol when treated either with B 3 followed by 2 2 and aq. Na, or with 2 S 4 / 2 : (many other answers are possible) 5. Two isomeric alkenes, A and B, that produce a 1:1 mixture of compounds C and D upon reaction with 3 followed by 2 2 and acid: Alkene A Alkene B 1. 3 2. 2 2 + C + D
Chem 203 midterm exam 1 p. 3 of 8 2. (16 pts.) Correlate the four 1 NMR spectra shown below with compounds E- (write your answer in the appropriate box). E C 3 F is the 1 spectrum of F is the 1 spectrum of G G is the 1 spectrum of is the 1 spectrum of E
Chem 203 midterm exam 1 p. 4 of 8 3. (11 pts.) A compound of formula C 10 12 produces the R and 1 NMR spectra shown below. Propose a reasonable structure for (write your answer in the box): the structure of compound is: 1690 3 2 2 3 2
Chem 203 midterm exam 1 p. 5 of 8 4. (18 pts.) Provide the structure of the major product expected from the following reactions. mportant: compounds incorporating multiple stereogenic centers must be drawn with the correct relative configuration. Note: it is understood that chiral compounds will be obtained as racemic mixtures. a. C 3 B 3, then 2 2 and aq. Na C 3 (or enantiomer) b. 2 2 (or enantiomer) c. 2 d. S S e. s 4, then aq. NaS 2 (or enantiomer) f. 2 S 4 2
Chem 203 midterm exam 1 p. 6 of 8 5. (20 pts.) Write an accurate mechanism for the following known reactions: a. = there is an here! Note: you will still receive full credit on this question if you omitted the second rearrangement, i.e., if you showed: product b. 2 ± + =
Chem 203 midterm exam 1 p. 7 of 8 6. (20 pts.) Propose a method for the preparation of compounds a. e. below starting from appropriate alkenes. Draw a clear structure of your proposed starting olefin on the left side of the reaction arrow. Above/below the reaction arrow, list all reagents / catalysts, in the correct order, that are required to induce the desired transformation. mportant: the desired compound must be the major product of your reaction(s). f a product does not appear to be available by any reaction known to you, write "NACCESSBLE" on the reaction arrow. Note: it is understood that chiral compounds will be obtained as racemic mixtures. a. 1. 3 2. Zn / + b. 1. s 4 2. aq. NaS 3 c. 1. B 3 2. 2 2, aq. Na d. 2 ( no rearrangement b/c reaction DES NT involve carbocations ) e. NACCESSBLE C 3
Chem 203 midterm exam 1 p. 8 of 8 Characteristic nfrared 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 4.2 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 2.4 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 4.0 Carboxylic acid C 11.0 12.0 (X =,, ) C X