CHEM 332: Spring 2014
Recitation Section 4/17/2014
+
18
1. When acetone is treated with H /H2O , the product acetone is found to be labeled with
Explain
H + / H 2O18
O
Me
Me
18
O.
O 18
Me
Me
2. Cyclopentanone forms ketal under acidic condition. However, it stops at hemiketal under
basic condition. In general, why aldehyde or ketones don t form acetals or ketals under basic
condition? Explain with suitable mechanism.
O
MeO
H + / excess MeOH
O
HO
OH- / excess MeOH
OMe
OMe
3. Predict the product from the following synthetic reactions:
O
H
N
p-toluenesufonic acid
Me
benzene, Δ
O
Me
Me
Me
p-toluenesufonic acid
Me
OH
HS
benzene, Δ
O
cat. HCl
H 2O
N
O
H 2O
cat. HCl
O
1.NH 2NH 2, H 2O, diethylene
glycol, NaOH, Δ
2. Η2Ο
O
Me
O
4. Dihydropyran reacts readily with an alcohol in the presence of a trace of anhydrous HCl to
form a tetrahydropyranal (THP) ether.
ROH
HCl
O
Dihydropyran
O
OR
Tetrahydropyranyl ether
(a) Write a plausible mechanism for this reaction. (b) THP ethers are stable in aqueous base
but hydrolyze rapidly in aqueous acid to yield original alcohol and another compound Explain.
(What is the other compound?). (c) The Tetrahydropyrany group can be used as a protecting
group for alcohols. Show how you might use it in a synthesis of 5-methyl-1, 5-hexanediol
starting with 4-chloro-1-butanol.
5. Predict the product and draw a arrow-pushing mechanism for it.
cat. HCl
N
H 2O