Chem 220a

                                Problem Set 9

                             Chapters 10 and 11

                          The Chemistry of Alcohols



                       Due: Monday, November 15, 1999



      You have two weeks for this Problem Set. There will be one more.

1) Review the Alcohol module in ORGO.

2) Design a synthesis of racemic 3R*,
4S*-1,3,4-

hexanetriol, using only ethylene and
acetylene

as your source of carbon atoms. All other

reagents are available to you. [Note: The *

designates relative configuration. The 3S*,

4R* enantiomer is also present.]

3) Compound A (C6H12) reacts with OsO4 to                 [Image]

form achiral B (C6H14O2). Treatment of B        Victor Grignard (1871-1935)

with H2SO4 gives ketone C (C6H12O). The          Nobel Prize (1912) shared
                                                           with
reaction of the Grignard reagent, tert-butyl
                                                 Paul Sabatier (catalytic
magnesium bromide, with acetaldehyde forms            hydrogenation)

D. Jones oxidation of D affords ketone C.

What are the structures of A-D? Provide a

mechanism for B ---> C.



4) A student attempts to convert
(±)-5-bromo-2-

pentanol (1) into
(±)-2-methyl-2,6-heptanediol

(2) by treating 1 with magnesium in ether


followed by the addition of acetone. Upon work-up of the reaction mixture in
aqueous acid, he could not

detect any 2 but he did isolate compound 3. A classmate suggests that he
first treat 1 with isobutylene in

the presence of a catalytic amount of sulfuric acid to form 4. She tells him
to run his Grignard reaction in

the same way [ 1) Mg, ether; 2) acetone; 3) H3O+] using 4 in order to
prepare 2. He does so and to his

delight he isolates 2. Help him understand what went wrong and how she
figured out how to solve the

problem. What are the structures of 3 and 4? What is the critical role of
isobutylene? [Hint: Think SN1.]



5) The oxidation of alcohols with Cr+6 or Mn+7 give Cr+3 and Mn+4 (MnO2) as
reduction products,

respectively. The KMnO4 oxidation on p.462 is not balanced. Write a redox
balanced equation for this

reaction. How many grams of KMnO4 are required to oxidize 0.1 moles of
1-phenylethanol to the ketone,

acetophenone? Does the reaction mixture become more or less acidic?



6) A student finds a bottle of Grignard reagent labeled "1.0 M RMgBr in
ether". To determine its structure,

she decides to add an excess of the Grignard reagent to 0.1 moles of the
ester, methyl n-butyrate (the

methyl ester of n-butyric acid). What is the minimum number of mLs of
Grignard reagent she needs to

add to the ester to obtain complete reaction [p. 438]? She isolates a single
compound A (C12H26O) after aqueous workup, which

when heated with a catalytic amount of H2SO4, forms a mixture of three
compounds (B, C, and D) all of

which have the formula C12H24. Ozonolysis of the mixture produces two
carbonyl compounds which

she separates upon careful distillation: 2-methyl-4-heptanone (from B and C)
and 2,6-dimethyl-4-

heptanone (from D). From the structure of these two ketones (actually, one
will suffice) she is able to

determine the structure of the Grignard reagent. She also recognizes that
two of the ozonolysis products E

and F were too volatile to isolate. What are the structures of A-F and of
the Grignard reagent? Explain

and illustrate her reasoning. [Hint: You can't distinguish between B and C
nor E and F.]



7) When optically-active compound A (C12H22) reacts with ozone followed by
zinc reduction to give 4-tert-

butylcyclohexanone and D. [Note: At this point you should know the structure
of A. Assign one of the

enantiomers to A. Why is A optically active? There are no asymmetric
carbons! How is this compound like

an allene!] Hydroboration of A followed by H2O2/NaOH gives two optically
active, diastereomeric

compounds B and C (C12H24O). [You can't distinguish between B and C; assign
them arbitrarily.]

When the tosylate of B or C is heated with C2H5ONa/C2H5OH, the enantiomer of
A (ent-A) is formed.

On the other hand, when B or C reacts with PBr3, the optically active
bromides E and F (C12H23Br) are

formed, respectively. Treatment of either E or F with refluxing
C2H5ONa/C2H5OH affords A , not its

enantiomer, ent-A. Explain and illustrate these results.



8) Provide reaction conditions for each of the following chemical
transformations. In a-c, where the number

of carbon atoms in the starting material and the product remain the same,
verify the total change in

oxidation level.

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