Problem Set 8
Chapter 9, Alkynes
Due: April 8, 2013
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Friedrich Wöhler (1800-1884)
(Wöhler possessed a wry sense of humor)
Connections Aluminum was once a precious metal although it was plentiful. The problem was how to remove it from its ore. Friedrich Wöhler, of urea synthesis fame, was able to accomplish this feat but by an impractical method. He was to meet a young chemist, Frank Jewett, recently arrived in Göttingen from Yale. Aware of the difficulty Wöhler had had and probably encouraged by Wöhler, Jewett, as a professor at Oberlin College, passed the problem onto Charles Martin Hall, a young student at the college. Hall solved the problem in his family garage. Thus was born Alcoa. At the same time in Spray, North Carolina, Thomas Willson, a Canadian, and American James Moorhead were unsuccessfully trying to refine aluminum using an electric arc. Unsuccessful in purifying aluminum, they sought calcium metal. Heating coal tar and lime in an electric furnace they obtained a brittle material that produced a combustible gas upon exposure to water. The material was not calcium nor was the gas hydrogen. The pair was calcium carbide and acetylene, the basis for Union Carbide Corporation (RIP).
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Charles Martin Hall (1863-1914)
The alkyne module in ORGO gives a good review of acetylene chemistry.
1. Provide the structures or reagents in each of the following questions. Explain your reasoning
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2. Compounds A and B are constitutional isomers. Determine the structures and reagents A-O. Explain your reasoning. |
3. Two bottles are found on a laboratory
shelf labeled "alkyne A" and "alkyne B".
Hydrogenation of A or B over a platinum
catalyst gives the same alkane C. Compound A
reacts with H2 in the presence of Lindlar's
catalyst to form D. Compound D reacts with
O3 to form a single compound E,
C3H6O. On the other hand, compound
B reacts with aq. H2SO4 in the
presence of HgSO4 to give two ketones J
and K. Under the same conditions, A gives
only J.
Compound B also reacts
with Na/NH3 to give F, which itself reacts
with Br2/H2O to give a pair of
constitutional isomers, G and H. Treatment of
either G or H with aqueous NaOH gives the same
compound I, C6H12O, that is
also formed by the reaction of F with peracid. What
are the structures of A-K? Explain and illustrate.
[Note: G and H are not distinguished from
one another. Pay attention to stereochemistry.] |
4. When racemic acetylenic alcohol 1, which bears a deuterium atom at the asymmetric carbon, was exposed to the potassium salt of 1,3-diaminopropane (KAPA, in place of NaNH2) in 1,3-diaminopropane as a solvent, racemic 2 was obtained in a "zipper" reaction after aqueous workup with 97% of the deuterium retained. [Note: You can find out about this reaction by Googling: alkyne zipper (mechanism) or see Problem 6 in the alkyne module of ORGO.] a) How many equivalents of KAPA are
required in this reaction? Explain.
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