Download chem 217 intermediate chemistry ii assignment #5 3/9/00 due: 3/23/00

CHEM 217 INTERMEDIATE CHEMISTRY II ASSIGNMENT #5 3/9/00 DUE: 3/23/00
ANSWER KEY
1.
Explain the difference in pKa's for the following dicarbonyl carbon acids: CH3COCH2CHO (5.9),
CH3COCH2COCH3 (8.9), and CH3COCH2CO2Et (10.7).
The differences are due to the fact that carbonyl groups of ketones and esters are less electronwithdrawing that those of aldehydes because alkyl (ketone) and alkoxy (ester) groups are electron
donating thus counteracting the electron-withdrawing effect of the carbonyl group. Thus, ketones
and esters don't stabilize the conjugate bases (enolates) as well as aldehydes do. Resonance structure
III below is the key resonance structure.
O
-O
O
-
O
O
R
O
R
R
I
II
III
R = H (aldehyde), CH3 (ketone) and OEt (ester)
The decreasing order of electron-withdrawing ability is CHO > COR > CO2R hence the order of pKa
values given. Resonance structures best illustrate this:
O
O
-
O
O
-
O
-
H
+
H
+
CH 3
H
aldehyde
H
H
H
H
H - not an EDG
H
+
ketone alkyl groups EDG by resonance
(hyperconjugation) and induction
O
O
-
O
R
R
R
+
O
O
O
+
ester
alkoxy groups EDG by resonance
Remember that the more resonance structures of approximately equal energy you can draw the
more stable the resonance hybrid.
2.
Provide a reasonable synthesis for each of the following compounds starting from the indicated
substrate and any other reagents you deem necessary.
O
a.
O
1) LDA
2)
O
Michael addition
(1,4 addition of an
enolate to an unsaturated ketone.
O


represents the where CC bonds were formed
NaOH
O
O


Intramolecular
Aldol condensation

-H 2O
-unsaturated ketone
HO

not isolated
-hydroxy ketone
b.
O
O
O
O
1) NaOEt
2) Br(CH2)5Br
3) NaOEt
OEt
ethyl acetoacetate
OEt
dialkylation
O
H3O+/
decarboxylation of -diacid
acetone derivative
c.
O
1) NaOEt
2) CH3I
O
OEt
O
O
dialkylation
3) NaOEt
4) CH3I
OEt
CH 3
ethyl acetoacetate
decarboxylation
of -diacid
CH 3
H3O+/
CHPh
O
CH 3
CH 3
Ph3P=CHPh
Wittig reaction
CH 3
CH 3
acetone
derivative
3.
The following compound is the result of an aldol condensation. What two carbonyl-containing
compounds was it made from? *
O
O

H
Ph
O

nucleophile
side
electrophile
side
cut  double bond and add 2 H's to the -side and
a =O to the -side
4.
Predict the major organic product(s) for each of the following reactions:
O
a.
Ph
+
O
O
1) LDA
Ph
2) PhCOOEt
O
O
b.
1) NaNH2
2) CH3CH2CH2Br
c.
1) Ph3P
CH 3
CH 3
2) CH3CH2CH2CH2-Li+
CH 3
Ph
(CH3)2CHBr
3) PhCOCH3
O
O
d.
CHO
1) NaOH
+
2) H3O+
Cl
Cl
OMe
OMe
e.
O
O
O
1) LDA, -78oC
2)
O
3) H3O+
O
f.
O
1) NaOH
O
2) H3O+
g.
CO 2Et
H3O+/
CO 2H
CO 2Et
O
O
h.
OEt
1) NaOEt
OEt
OEt
2) H3O+
O
O
i.
O
O
OH
O
3) NaOEt
1) SOCl2
2
O
2
OEt
2) EtOH
O
OEt
4) H3O+
O
O
5) NaOEt
+
7) H3O /
CH 2Ph
OEt
6) PhCH2Br
CH 2Ph
j.
O
O
1) NaOEt
O
O
2) NaNH2
CH 3CH 2
3) CH3CH2Cl
4) H3O+
k.
O
O
O
1) xs. I2/NaOH
2) H3O+
3) SOCl2
OH
4) EtOH
OEt