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Chemistry 251/253 |
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Homework 3 |
1. LiAlH4 is a more powerful reducing agent than NaBH4 because
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2. The stereochemistry of the 1-phenyl-1,2-propanediol formed in
the reaction
would be
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H. an equimolar mixture of (1S,2S) and (1S,2R) |
3. 
is
a(n)
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4.
is
a(n)
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5.
is a(n)
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6. Draw the structure of compound A in the reaction
O=C1CCCC1
7. Draw the structure of the aldehyde or ketone from which you
would prepare 
.CCC(C)C(=O)C
8. Draw the structure of compound B in the following reaction
sequence:
CC(C)OC(O)c1ccccc1
9. Arrange the following compounds in order of increasing rate of
protonation:
A<B<C<D
The compound that produces the most stable carbocation will be formed
the fastest. To rank the carbocations draw them out and then answer
the following questions- 1. Is this ion stabilized by resonance? 2.
How many hyperconjugative interactions help to stabilize this
ion?
10. Al Keene isolated an unknown compound, C, from a rare variety of rubber tree. Elemental analysis indicated that compound C contained 91.2% C and 8.8% H. Ozonolysis of this material produced acetophenone and another compound, D, that gave the attached 1H-NMR spectrum. Catalytic hydrogenation of C under forcing conditions produced E, which contained 86.5% C and 13.5% H. The 13C-NMR spectrum of compound E contained 6 signals, all of which fell between 15 and 35 ppm. These transformations are summarized below. Draw the structure of compound C.CC(=C1CCCC=C1)c2ccccc2
11. Organic chemists would describe the reaction
as
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12. Draw the structure of the product of the following
reaction:
C1CCC(=Nc2ccccc2)C1
13. 
may
be prepared by the reaction of an amine with a carbonyl compound.
Draw the structure of the carbonyl
compound.CCC(C)C(=O)C 
Questions 14 and 15 involve the following reaction:
15. Draw the structure of compound G.CC1CCCCC1(C)NC2CCCC2
16. How many of the following compounds would you expect to be oxidized by CrO3/H2SO4/H2O? 3 You should use alcohols and ketones as models for these compounds. The first three all contain the fragment H-C-N-H, which is analogous to the H-C-O-H fragment that is required for oxidation. The last two fragments compounds are analogous to ketones. They are stable to oxidation.
17.Draw the structure of the carbonyl compound you would use to
prepare the amino acid isoleucine ,
,
by a Strecker synthesis.
CCC(C)C=O
18. Draw the structure of the product of the following
reaction:
NC(=O)NN=C1CCCC2CCCCC21
19. Select the species that would be present in lowest concentration in the following equilibrium. Assume a limited amount of acid.B Since N is less electronegative than O, the amino group of the amino alcohol will be protonated before the hydroxyl group. Thus, C is preferred over B. Protonation of the carbonyl oxygen generates ion A, which is a resonance stabilized ion and should therefore be formed more readily than B which is not stabilized by resonance.
20.Select the product that is most likely to be formed after work-up of the reaction shown in Question 19: D The reaction would produce compound B initially. This would lose a molecule of water to produce C, which would then undergo intramolecular addition of the OH group to the (protonated) C=N group.
From a retrosynthetic perspective, the Wittig reaction involves
the following disconnections:
assuming that the other starting material is a
ketone.CCBr
22. How many of the following compounds are not compatible with the Wittig methodology implied by the retrosynthetic perspective shown above? 3 The first, third, and fifth compounds do not have a hydrogen atom bonded to the same carbon atom as the bromine.
23. Draw the structure of the product of the following
reaction:
CC[CH-][P+](c1ccccc1)(c2ccccc2)c3ccccc3 or CCC=P(c1ccccc1)(c2ccccc2)c3ccccc3
24. Arrange the following isomeric compounds in order of increasing rate of reaction with triphenylphosphine. B<C<A The reaction proceeds by an Sn2 mechanism. Aryl halides do not undergo Sn2 reactions, so compound B is the slowest. A and C are both 1o alkyl halides, but A is a benzylic halide, so it reacts faster than C.
25. Draw the structure of the product of the following
reaction:
OCCCCC=C
This reaction is a simpler version of the last example given in the
topic dealing with the Wittig reaction.
26. Select the reaction that would be least satisfactory for the preparation of 1-butene.B This reaction would be more likely to produce 2-butene than 1-butene.
27. Draw the structure of the product of the following
reaction:
[Br-].CCC[N+](C)(C)C
28. Draw the resonance structure that makes the most important contribution to the resonance stabilized ion that is formed in the following reaction:
CC(=O)C=P(c1ccccc1)(c2ccccc2)c3ccccc3
The positive and negative charges are separated
in the first and third structures. In the middle structure none of
the atoms are charged and there is one more bond than in the other
structures.
29. An unknown compound, X, contained 81.4% C and 8.7% H. It
rapidly decolorized a solution of KMnO4, but did not react
with 2,4-dinitrophenylhydrazine. Ozonolysis of this compound produced
benzaldehyde, C6H5CHO, and another compound
that gave the attached 1H-NMR
spectrum. Deduce the structure of compound X.
COCC(=Cc1ccccc1)C
30. An unknown compound, Y, contained 68.9% C and 12.7% H. It did
not react with a solution of KMnO4, nor with
2,4-dinitrophenylhydrazine. Treatment of this compound with aqueous
acid produced ethanol and another compound that gave a positive 2,4-D
test. This compound had a 13C-NMR spectrum that contained
signals at 19.5, 22.7, 49.8, and 212.8 ppm. Draw the structure of
compound Y.
CCOC(CC(C)(C)C)OCC or CCOC(C)(OCC)C(C)(C)C or CCOC(OCC)C(CC)CC Compound Y is a ketal or an acetal . The ketal hydrolyses readily to produce ethanol and 3,3-dimethyl-2-butanone, while the first acetal yields ethanol and 3,3-dimethylbutanal and the second acetal is hydrolysed to ethanol and 2-ethylbutanal.
