ALPHA CARBON CHEMISTRY: ENOLS AND ENOLATES
A STUDENT SHOULD BE ABLE TO:
1.
Identify α-carbons, α-hydrogens, and the bases strong enough to deprotonate the αcarbons.
2.
Draw the mechanisms for acid-catalyzed and base-catalyzed keto-enol tautomerization.
3.
Predict products of and propose syntheses using the following types of reactions:
Acid-catalyzed halogenation of ketones at the α-position
Hell-Volhard-Zelinski reaction
Haloform reaction
Aldol reaction and aldol condensation. Aldol reaction products are formed
without heat (room temperature or lower). Aldol condensation products occur
under high temperatures or when extended conjugation within the product can
be achieved.
Claisen condensation
Alkylation of enolates
Acetoacetic ester synthesis (alkylation at the α-carbon)
Michael additions
4.
Propose mechanisms for, and predict and interpret experimental results on the basis of
mechanism, for the following reactions:
Keto-enol tautomerism
Aldol, crossed aldol, and related condensations
Decarboxylation of beta-keto acids
Claisen condensation
Acetoacetic ester synthesis
Michael additions
To best prepare for this module, please work Chapter 22 Skill Builder problems in the textbook.
A STUDENT WHO HAS MASTERED THE OBJECTIVES FOR THIS UNIT SHOULD BE
ABLE TO SOLVE THE FOLLOWING PROBLEMS AND RELATED ONES:
1.1
In the following acid-catalyzed tautomerization, identify the keto and enol forms. For the
keto form, circle the -carbons and hydrogens.
1.2
Which of these bases deprotonates acetone irreversibly? Use pKa data from your book.
a) CH3CH2-
b) CH3CO2-
c) Br-
d) (CH3)2CHNH-
e) CH3O-
1.3
Which of the bases shown in Problem 1.2 deprotonates acetone reversibly?
2.1
Draw the enol product. Then, show the mechanism for the base-catalyzed tautomerization
of acetone.
2.2
Draw the structure of the keto tautomer of phenol.
3.1
Predict the product(s) of each of the following reactions.
3.1
O
g)
1. NaOH, heat
2. dil. H+
3.2
Propose a synthesis of each of the compounds shown, from the starting material(s)
specified and any other needed reagents or solvents.
b) 2-pentanone from ethyl bromide
3.2
O
d)
f rom
O
OH
3.3
Predict the product(s) of the following reactions of α,β-unsaturated ketones.
3.3
4.
Propose a mechanism for each of the following reactions.
5.1
Of the following compounds: a) which one turns blue litmus red when dissolved in
water? b) Which is neutral to litmus when dissolved in water? c) Which is insoluble in
water but soluble in 5% NaOH(aq) and 5% NaHCO3(aq)? d) Which is insoluble in both
water and NaOH(aq)?
SOLUTIONS TO SAMPLE PROBLEMS:
1.1
1.2
pKa for conjugate acid, with data from Table 3.1. If exact molecule is not available, the
closest example is given.
d) (CH3)2CHNHe) CH3Oa) CH3CH2- b) CH3CO2- c) Br50
4.75
~7
~38
~16
The pKa for acetone is 19.2. Only the bases with weaker conjugate acids will deprotonate
acetone irreversibly: a and d
1.3
Using the data above, only bases with conjugate acids with similar pKa to acetone will
deprotonate acetone reversibly: e
2.1
2.2
The keto tautomer of phenol:
3.1
Predict the product(s):
3.1
3.2
Propose a synthesis:
3.2
LDA
d)
(CH3)2CH-CH=O
H2O
O
O
OH
O
O
f)
3.3
CN
NaOH
1. NaCN
heat
2. dil. H+
OH
O
1. CH3CH2MgBr
a)
H
2. H3O+
H
O
3.3
O
O
O
O
KOH
c)
4.
Mechanisms:
5.1
a)
e
O
H
H3O+
O
b)
d
c)
a
d)
c
Name ______________________________________________
Organic Chemistry 2220D
Eighth Drill Test (Sample A)
Answer All Questions
1.
Circle all  carbons, and draw in all  hydrogens.
2.
Predict the product(s) of each of the following reactions (if any):
O
a)
H
NaOH
+
O
3.
Propose a mechanism for each of the following reactions:
Name ______________________________________________
Organic Chemistry 2220D
1.
Eighth Drill Test (Sample B)
Answer All Questions
Circle the bases that are often used to generate the enolate from CH3CH=O.
a) NaOH
b) CH3ONa
c) NaCl
d) NaH
e) NaNH2
Which of the bases above generate the enolate from CH3CH=O reversibly?
2.
Which of the following compounds does not have  protons?
a) H2C=O
b) C6H5CH=O
c) (CH3)3CCH=O
d) CH3CH2CH2CH=O
3.
Predict the major organic product(s) of the following reactions.
4.
Draw the enol tautomer of the ketone shown.
5.
Propose a mechanism for each of the following reactions.
OH
O
+
a)
H3O
5.
6.
Which of the following is an intermediate in the mechanism of the reaction shown?
7.
Which of the following compounds is NOT a product of the aldol reaction shown?