39H
Quiz Chemistry 2
Tuesday February 13, 2007
Name (printed) KEY
Signature
This quiz consists of three questions -- check that you have them all. A perfect score on this quiz is
30.
------------------------------------------------------------------(10)
1
(10)
2
(10)
3
TOTAL
1
_______
Name ________________________
(10) 1. Circle the correct answer.
(2) a. Which of the following compounds will have the smallest equilibrium constant (Keq) for the
reversible reaction with HCN?
O
O
a)
b)
H3C
CH3
O
c)
H
CH3
H3C
O
d)
CF 3
H
CF3
(2) b. Use of a labeled version of LiAlH4, LiAlD4 (D = deuterium, an isotope of hydrogen), in the
reduction of cyclohexanone (1) furnishes
O
1) LiAlD4
2) H3O+ quench
1
H
OH
H
a)
OD
D
b)
OH
D
c)
OD
d)
(2) c. Which species is most susceptible to nucleophilic attack (= highest rate of attack)?
R
CH3
H + CH3
N
H
N
R
(a)
(2) d.
H
R
(b)
H
R
H
(d)
(c)
How many stereoisomers (enantiomers and diastereomers) could result from addition of 2
equivalents of CH3Li (followed by H3O+ quench) to 1?
O
O
H
H
a) 3
b) 4
(2) e.
H 3C O O C H 3
O
1
c) 5
d) 6
Which conformation is relevant to predicting the outcome of chelation-controlled nucleophilic
addition to an aldehyde?
P
M
P
O
H
O
H
O
H
R
R
2
M
O
H
P
R
H
H
O
O
M
Name ______________________________
(10) 2. Provide short answers to the following questions.
(5) a. In principle, aldehyde 1 can trimerize acid under catalysis to furnish the trioxane product 2.
R
O
R
H + cat.
H
O
R
O
O
1
R
2
Estimate the overall enthalpy of this transformation using the bond dissociation energies given below.
Sketch the lowest energy conformation of 2. Be careful in your explicit depiction of stereochemistry.
Bond dissociation energies (kcal/mol)
C-H
99
C-O
91
C-C
85
RO-H
102
C=O
175
C=C
146
H-OH
119
HO-H
119
Bonds Broken
3 x C=O
Bonds Made
525 kcal/mol
6 x C O
546 kcal/mol
!H = bonds broken bonds made = 525 546 = -21 kcal/mol
R
O
O
O
R
R
(5) b. Predict the product of kinetically controlled addition of HCN to aldehyde 1 using Cram's model.
Pay careful attention to your depiction of stereochemistry. Indicate the key conformation/steric
interactions that lead to the stereochemical outcome that you show.
O
HCN
HO CN
H
H
H+
1
CN
H
i-Pr
H
least hindered
vector of attack
O
CH3
preferred Cram-type conformation
3
CN
i-Pr
H
H
O
CH3
Name ________________________
(10) 3) Provide a detailed mechanistic description for the interconversion of aldehyde 1 and
ketone 2. Please make sure that you are clear in your depiction of structures, equilibria,
etc.
O
O
H
O
cat. H+
O
OH
1
2
H
OH
H+
O
H+
+O
H
O
H
+O
H
This intermediate will probably lose
stereochemistry at H via
deprotonation/reprotonation, but that
subtlety is not a crucial part of the
mechanism.
O
H
4
H
OH
H
H
OH
+H
O
H
H
O
O
H
O+
H
O
H
OH
H
O
O+
H