Page 481 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

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462 4.5. Both endo- and exo-norbornyl brosylates react with R P N (R is a long-chain
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3
alkyl) in toluene to give azides of inverted configuration. The yield from the
CHAPTER 4
endo and exo reactant is 95 and 80%, respectively. The remainder of the exo
Nucleophilic Substitution reactant is converted to nortricyclane (tricyclo[2.2.1.0 ]heptane.) The measured
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rates of azide formation are first order in both reactant and azide ion. The
endo isomer reacts about twice as fast as the exo isomer. Both react consid-
erably more slowly than cyclohexyl brosylate under the same conditions. No
rearrangement of deuterium is observed when deuterium-labeled reactants are
used. What conclusions about the mechanism of the substitution process can you
draw from these results? How do the reaction conditions relate to the mechanism
you have suggested? How is the nortricyclane formed?
4.6 The following observations have been made concerning the reaction of
Z-1-phenyl-1,3-butadiene (6-A) and Z-4-phenyl-3-buten-2-ol (6-B) in
3–7MH SO and 0 5–3MHClO 4
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a. Both compounds are converted to a mixture of the corresponding E-isomers
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with the rate governed by Rate = k reactant H , where H is measured
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by the H acidity function.
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b. The rate of isomerization of 6-A is slower in deuterated D SO -D O media
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by a factor of 2 to 3. For 6-B, the rate of isomerization is faster in by a factor
of 2.5.
c. When 18 O-labeled 6-B is used, the rate of loss of 18 O to the solvent is equal
to the rate of isomerization.
d. The measured activation energies for 6-A is 19 5 ± 1kcal/mol and 22 9 ±
0 7kcal/mol for 6-B.
Write a mechanism that encompasses both isomerizations and is consistent with
the information given.
4.7 Treatment of 2-(4-hydroxyphenyl)ethyl bromide with basic alumina produces a
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white solid, mp, 40–43 C; IR 1640cm ;UV max 282 nm in H O; NMR two

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singlets of equal intensity at 1.69 and 6.44 ppm from TMS; anal: C 79.98% H,
6.71%. Suggest a possible structure for this product and explain how it could be
formed.
4.8. In the discussion of the syn- and anti-norborn-2-en-7-yl tosylates (p. 422–423) it
was pointed out that, relative to the saturated norborn-7-yl tosylate, the reactiv-
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ities of the syn and anti isomers were 10 and 10 , respectively. Whereas the
anti isomer gives a product of retained configuration, the syn isomer gives a
bicyclo[3.2.0]hept-2-enyl derivative. The high reactivity of the anti isomer was
attributed to participation of the carbon-carbon bond. What explanation can you
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offer for the 10 acceleration of the syn isomer relative to the saturated system?
4.9. Indicate the structure of the final stable ion that would be formed from each of
the following reactants in superacid media.

a. HO b. c. d.
OH CH2CH2Cl
Cl

e. f.
CH OH
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