1. No category

CHEM 234, Spring 2015
Second Midterm
ANSWER
PRINTED
FIRST NAME
Ian R. Gould
KEY
PRINTED
LAST NAME
ASU ID or
Posting ID
Person on your LEFT (or Aisle)
Person on your RIGHT (or Aisle)
synth
1__________/20.........................
• PRINT YOUR NAME ON EACH PAGE!
rxns
2__________/36........................
• READ THE DIRECTIONS CAREFULLY!
ether
3__________/18..........................
• USE BLANK PAGES AS SCRATCH PAPER
mxn
4__________/38..........................
work on blank pages will not be graded...
Grignard
5__________/21
.........................
•WRITE CLEARLY!
peri 1
6__________/18.........................
• MOLECULAR MODELS ARE ALLOWED
peri 2
7__________/24.........................
• DO NOT USE RED INK
• DON'T CHEAT, USE COMMON SENSE!
Total (incl Extra)________/175+5
Extra Credit_____/5
H
He
Li Be
B
N
O
F
Ne
Na Mg
Al Si P
S
Cl
Ar
Ga Ge As Se Br
In Sn Sb Te I
K
Ca
Rb Sr
Cs Ba
Sc Ti V
Y
Cr Mn Fe Co Ni Cu Zn
Zr Nb Mo Tc Ru Rh Pd Ag Cd
Lu Hf Ta W
small range
range of values
broad peak
Re Os Ir Pt Au Hg
O H
C N
N H
C O
C
Tl Pb Bi Po At
H
C
C
N
C
Rn
Me/Et
1600–1660
10
200
R C OH
Approximate Coupling
Constants, J (Hz), for
1H NMR Spectra
H H
H
~7
H
H
~10
C C
OR
1735
CH
~8
H
1600
O
NR2
H
O
C CH3
–H2C NR2
7
140
6
120
5
100
Aromatic
CR2
C CH
4
80
3
60
RC
CR
Alkyl
3Y > 2Y > 1Y
2
40
–OCH2–
R C N
R2C
H
~15
C C
1500
C CH2
8
160
~2
H
C
–OCH2–
NMR Correlation Charts
H
H
1650
2000
~2
C C
O
Aromatic Ar H
mainly 8 - 6.5
O
C
~2.7
1680
C
2500
9
180
t-Bu/Me
O
1710
3000
11
220 O
~1.1
~2.9
N
–H2C X
(δ, ppm)
~0.95
i-Pr/Me
C C
2200
amine R NH2 variable and condition
alcohol R OH dependent, ca. 2 - 6 δ
O
C H
Et/Me
~2.6
C
C
C
O
C O H
O
R C OH
~1.4
H
2850–2960
3500
~0.9
C
broad ~3000
(cm-1)
Me/Me
H
broad with spikes ~3300
broad ~3300
Me/Me
O
2200
O H
H/Me
Xe
C
2720–2820
2 peaks
3000–
3100
N H
Kr
H
C
3300
~1.0
Infrared Correlation Chart
H
Gauche
Eclipsing
H/H
usually
strong
O
C H
Interaction Energies, kcal/mol
1
20
0
0
Alkyl 3Y > 2Y > 1Y
C X
C NR2
-2-
CHEMISTRY 234, Spring 2015 MIDTERM #2
NAME
There is no need to ask Dr. Gould or any of the TAs, there is NO NOMENCLATURE
problem on this test!
Question 1 (20 pts.) Show how you would make the target compond on the right from
the starting compound on the left. Show reagents and conditions where appropriate,
and the structures of important intermediate compounds. Do not show any (arrow
pushing) mechanisms. Ignore stereochemistry.
O
PCC
NBS/hν
OH
Br
1. BrMg
K+ –O-t-Bu
1. BH3.THF
2. –OH/H2O2
O
OH
PCC
2. H3O+
H
Extra Credit Question (5 pts.) In which kind of biomolecule can a photochemical 2 + 2
cycloaddition reaction take place
DNA
phospholipid
carbohydrate
protein
-3-
CHEMISTRY 234, Spring 2015 MIDTERM #2
NAME
Question 2 (36 pts) Give the major organic products of the following reactions, indicate the
stereochemistry using wedged/dashed bonds as appropriate and be sure to indicate the presence
of any racemic mixtures. State whether a solution of the product(s) would be optically active
or not, with a very brief explanation.
HO
O
Na+ –OEt
optically active
H
a)
H
single enantiomer
EtO
EtOH
Cl
1 Equiv. HCl
b)
(±)
NH2
NH2
c)
NOT optically active
racemic mixture
CF3
Δ
+
(±)
NOT optically active
racemic mixture
CF3
O
Ph
1. Excess Ph-MgBr
O
d)
OH
OH
Ph
2. H3O+
NOT optically active
achiral
Question 3 (18 pts) Draw the structures of the alcohol, the deprotonated alcohol and alkyl halide
in the appropriate boxes you would use to complete the best WIlliamson ether synthesis of the
provided ether, and fill in the base reagent required to deprotonate the alcohol
NaH
base
OH
O
+
Br
O
Na
alcohol
deprotonated
alcohol
alkyl halide
-4-
CHEMISTRY 234, Spring 2015 MIDTERM #2
NAME
Question 4 (38 pts.) For the following reaction, give a full curved-arrow pushing mechanism for
formation of products A and B. Indicate the Lewis acid and base at each step (LA or LB) and
whether they are also Bronsted acids and bases (BA or BB). Include all reasonable
resonance contributors for any intermediates AND INDICATE THE MAJOR RESONANCE
CONTRIBUTOR as APPROPRIATE!
OCH3
Br H
H3CO
CH3OH (solvent)
+
(±)
(±)
B
A
LA/BA
HBr cat.
OR... LB/BB
CH3LA/BA
LB/BB
Me
H
H O
O H
O
Me
H
LB H
Me
H3C
Me O
O
H LB
LA/BA
O H
H
H
O
H
Me
LB/BB
LA
MAJOR
number of steps in the mechanism for product A
number of steps in the mechanism for product B
3
3
b) Indicate which product, A or B, would be formed under thermodynamically controlled
conditions and which would be formed under kinetically controlled conditions and give a BRIEF
explanation of the role of temperature in determining kinetic and thermodynamic control
kinetic = A, thermodynamic = B, B is more likely to be formed at HIGH temperature since higher
temperature enables REVERSIBLE reactions and allows the reaction to explore the entire
reaction energy surface and find the lowest energy product, at low temperatures the reactions are
irreversible and the fastest formed product is the major product
c) Draw an energy diagram for formation of both A and B ON THE SAME DIAGRAM, clearly
indicate which curve refers to formation of A and which to formation of B.
B
Energy
A
A
H3CO
+ CH3OH
+ CH3OH
OCH3
B
reaction coordinate
-5-
CHEMISTRY 234, Spring 2015 MIDTERM #2
NAME
Question 5 (21 pts.) In the provided structure, identify THREE carbon-carbon bonds that can be
made using a Grignard reaction, give the structures of the Grignard and the molecule that it
reacts with, acid workup steps (H3O+) are assumed you do not need to include them. CLEARLY
indicate the C-C bond you are making in each reaction with an arrow
O
MgBr
O
+
+
OH
H
OH
Me–MgBr
OH
O
+
H
BrMg
Question 6 (18 pts) For the following electrocyclic ring closure reaction
F3C
D
CF3
use THIS structure for the
drawing of the HOMO
D
D
D
heat
F3C
D
CF3
H
F3C
H
CF3
D
use THIS structure for the
curved arrow-pushing
a) give the curved arrow-pushing that describes the bond-making and bond breaking
b) on TOP of the reactant, draw a representation of the wavefunction of the HOMO usign the
approximate "p A.O." method (assume that the structure is slightly tilted so that you can see
the phases of the orbital
c) does the allowed reaction proceed via a conrotatory or disrotatory ring closure?
disrotatory
__________________________
-6-
CHEMISTRY 234, Spring 2015 MIDTERM #2
NAME
Question 7 (24 pts). Give the ALLOWED product of the following cycloaddition reaction
CN
*
heat
+
*
CN
A
B
CN
CN
*
*
OR
CN
CN
not optically active, MESO compound
a) Give the curved arrow-pushing that describes the bond-making and breaking.
b) Redraw the cation A and give a pictorial
representation of the wavefunction of the
HOMO ON TOP OF THE STRUCTURE
c) Redraw the dicyanoethylene B and give a
pictorial representation of the wavefunction
of the LUMO ON TOP OF THE STRUCTURE
bonding
CN
bonding
CN
d) Is the allowed reaction suprafacial/suprafacial or suprafacial/antarafacial, give a brief
explanation based on your drawings of the molecular orbitals, you MUST include the following
terms: HOMO, LUMO, transition state
the ALLOWED product of the reaction must have two bonding interactions in the
transition state, consideration of the wavefunctions of the HOMO and the LUMO
indicates that suprafacial/suprafacial reaction is allowed, thus the 2 -CN groups start cisand are on the same side in the product, and the two Me-groups on the outside of the
cation end on the same side in the product
e) Indicate ALL of the chiral/asymmetric centers in the product of the reaction using the * symbol,
and explain whether a solution of the product would be optically active or not and why or why not