Page 639 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

6.4 a. The relative rates of hydroxide ion-catalyzed deuterium exchange at C(3) 621
have been measured for bicyclo[2.1.1]hexan-2-one, bicyclo[2.2.1]heptan-2-
one, and bicyclo[2.2.2]octan-2-one. What factor(s) could account for the much PROBLEMS
smaller rate of exchange for bicyclo[2.1.1]hexan-2-one?
b. Treatment of (+)-camphenilone with K · O-t-Bu in t-BuOD at 185 C results
+ −

in incorporation of D, as indicated below. Racemization occurs at the same
rate. Suggest a mechanism that could account for these observations.

CH 3
D
CH 3
D D O

6.5. Using data from Tables 6.1 (p. 580) and 6.2 (p. 583), estimate the extent of
deprotonation for each hydrocarbon-base combination below. Discuss the uncer-
tainties that could affect the calculation.

a. indene by 0.01 M NaOCH in 1:1 DMSO-C H OH
3 2 5
b. fluorene by 0.01 M NaOC H in 20:1 DMSO-C H OH
2 5 2 5
c. triphenylmethane by 5 M KOCH in CH OH
3 3
6.6. The rates of removal of axial and equatorial protons from 4-t-butylcyclohexanone
in NaOD/dioxane have been compared by an NMR technique. The rate of
removal of an axial proton is 5.5 times faster than for an equatorial proton. How
do you explain the difference?
6.7. The following table gives exchange rates in methanolic NaOCH and pK values
3
for some hydrocarbons. Determine if there is a correlation between the kinetic
and thermodynamic acidity.

Compound k exchange pK
M −1 −1 4
s ×10
9-Phenylfluorene 173 18.5
Indene 50 19.9
3,4-Benzofluorene 90.3 19.75
1,2-Benzofluorene 31.9 20.3
2,3-Benzofluorene 2.15 23.5
Fluorene 3.95 22.7

6.8. The acidity of various substituted acetophenones in DMSO is given below.
Would you expect the value to correlate best with
,
,or
? Explain,
+
−
considering each of the
parameters explicitly. Do a plot of the pK/pK values
0
for each
parameter.
O
X CH 3