FINAL EXAM
Organic Chemistry
Chemistry 220a; 9 A.M., Friday, December 17, 2004
NAME (print): ______________________________________________________________
TA:_____________________ Section Day:_____________ Section Time:______________
Take a few moments to look over the exam. Do problems first with which you are most comfortable. Important points and unknowns are in bold type. Do all preliminary work on the worksheets. The worksheets will not be graded. The exam is 2 to 2-1/2 hours with an additional 1/2 hour for review. STOP writing when you are asked to do so. Put your name on the cover sheet and subsequent pages (except for Work Sheets) where indicated.
Question 2: Do 4 of 6.
Question 3: Do 6 of 8.
Question 4: Do 4 of 6.
.
Remember: Neatness is to your advantage.
Have a GREAT winter
break! See you next term for Chem
221b.
1. Spectrometry/Structure I (30 pts) ________ 5. Spectrometry/Structure II (30 pts) _________
2. Reactions I (32 pts) _________ 6. Mechanisms (20 pts.) _________
3. Potpourri (48 pts) _________ 7. Synthesis (29 pts.) _________
4. Reactions II (32 pts) _________ 8. Radicals (29 pts.) _________
__________________________________________________________________________________
Total (250 pts)
1. (30 pts) Spectrometry/Structure
I: A pair of students synthesize 2-, 3-,
and 4-heptanol. Upon arriving at
the lab the next morning, they discover that the labels have fallen off the
bottles containing their samples.
He wants to redo the syntheses but she suggests that they record the
mass spectrum of each of the samples to determine their structures.
Heptanol A Heptanol B
Heptanol C Alkyl Halide D
a) (18 pts) Assign structures to heptanols A, B, and C. Show your reasoning. [You do not have to account for all the peaks or even some of the more intense ones, only the ones that distinguish one structure from another.]
Continued on the next pageÉ
b) (12 pts) The students prepared one of the heptanols from alkyl halide D and n-butyraldehyde (butanal). Identify alkyl halide D (show your reasoning) and show how and which heptanol was prepared.
2. (4 x 8 pts = 32 pts) Reactions I: Provide the reagents (and conditions, if necessary) required to complete 4 of 6 of the following chemical transformations. Several steps may be required. If you complete more than four questions, cross out the ones that you do not want graded.
3. (6 x 8 pts = 48 pts) Potpourri: Complete 6 of 8 of the following questions. If you complete more than six questions, cross out the ones that you do not want graded.
a) Circle the compound with the greatest heat of combustion.
b) Circle the mass spectral pattern that most closely resembles the ion CHCl2+. (Each hash mark is a mass unit.)
c) For n-octane at 25oC: DHf0= -49.8 kcal/mol; DH0(combustion) = - 1,317 kcal/mol. Estimate the heats of formation and combustion for n-heptane. Show work.
d) Given that the relative rates in free radical chlorination are: 10 = 1; 20 = 4.5; 30 = 5.5, provide the structure and percent of the major free radical monochlorination product of 2,4-dimethylpentane. Show work.
e) Complete each of the following true or false questions.
i) All meso compounds have an associated d,l-pair. T ___ F ___
ii) All d,l compounds have an associated meso compound. T ___ F ___
iii) All conformations of meso compounds are achiral. T ___ F ___
iv) All achiral compounds are meso. T ___ F ___
f) Circle the third compound in order of pKa.
acetic acid phenol b-chloroethanol propyne ammonia
g) Circle the compounds that contain atoms with sp2 hybridization.
vinylacetylene(C4H4) BEt3 acetone dimethyl sulfoxide cholesterol
h) The optical
rotations of the enantiomers of limonene have been reported as [a]D = +1250 and [a]D = -1000. Assuming only one of the enantiomers is
pure and other one is contaminated with its enantiomer, determine the
enantiomeric excess of the impure sample. Show work.
4. (4 x 8 pts = 32 pts) Reactions II: Complete 4 of 6 of the following questions, but you must do either 4a or 4f. If you complete more than four questions, cross out the one that you do not want graded.
5. (30 pts) Spectrometry/Structure II: Compound
A, whose mass spectrum is shown,
is inert to PCC and hydrogenation. Compound A is readily converted into compounds B (minor) and C (major) upon exposure to H2SO4. Ozonolysis and dimethyl sulfide
reduction of B affords compound D (C5H10O), which is inert to
Jones reagent, and compound E. Treatment of C with cat. OsO4/HIO4
gives rise to compounds F and G, both of which have the same molecular
formula. Compound F is
inert to cold aq. KMnO4, but compound G reacts with cold aq. KMnO4 to form H. What
are the structures A-H? Explain and illustrate.
6. (20 pts) Mechanisms: Provide a mechanism (curved arrow formalism) for one, and only one, of the following reactions.
a) Hydroboration and oxidation of (E)-3-methyl-2-pentene.
b) Ozonolysis and reduction of (E)-3-methyl-2-pentene.
c) The formation of pinacolone (3,3-dimethyl-2-butanone) from pinacol.
7. (29 pts) Synthesis: Design a synthesis of 3-ethyl-2-methyl-3-hexanol from propene as the exclusive source of carbon. All reagents are available.
8. (29 pts) Radicals: Determine the heat of formation of chlorocyclohexane given the bond dissociation energies on page 14 and the following heats of formation (kcal/mol): n-hexane, -40.0; cyclohexane, -29.5; HCl, -22.1. Show work.