Unformatted text preview: Chemistry 262
Iha ANSWER KEY Problem Set 4 CHAPTER 18
ALDEHYDES AND KETONES
QUESTION 1 MECHANISMS Acid Catalyzed Addition
A) Draw the mechanism for the acid catalyzed formation of the dithiane shown below
B) Draw the mechanism for the acid catalyzed formation of the acetal shown below
C) Acetal formation (as well as dithiane formation) is an equilibrium reaction. As such, the reaction can be reversed. Show how the
acetal group can be removed and the ketone can be reformed through a reaction with water.
Problem Set 4
QUESTION 1 MECHANISMS Acid Catalyzed Addition cont.
D) The Wolff
Kishner reduction is a method for deoxygenating a carbonyl to produce an alkane.The first step in the Wolf
Reduction is the formation of a hydrazone (a type of immine) through the reaction of a ketone or aldehyde with hydrazine. Draw the
mechanism for this step based upon the reaction below.
The second step involves reaction of the hydrazone with hydroxide to yield the alkane and nitrogen gas. Draw the mechanism for this
step in the Wolff
Kishner Reduction based upon the reaction below.
E) Draw the mechanism for the acid
catalyzed generation of the enol shown below
Iha ANSWER KEY Problem Set 4 QUESTION 2: Practice Problem
The following dithiane can be formed by the reaction of formaldehyde with a dithiol. If you would like more practice, draw the
mechanism for the generation of the dithiane shown below.
This dithiane can undergo a series of useful reactions/transformations to yield aldehydes and ketones. Fill in the boxes bel ow with the
products resulting from each step.
QUESTION 3: Practice ProblemDithianes can make excellent nucleophiles (as shown in question 3). Good nucleophiles are also
known for reacting with ketones and and aldehydes. Fill in the boxes below with the products resulting from each step.
Problem Set 4
QUESTION 4: Mechanisms
A) Draw the mechanism for the oxidation of benzaldehyde in the presence of water, acid and CrO3 (i.e. conditions for the Jones
B) Draw the mechanism and resulting product for the Wittig reaction shown bellow
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