CHEM 234
Ian R. Gould
the exam cover sheets look kind of like this
PRINTED
FIRST NAME
PRINTED
LAST NAME
ASU ID or
Posting ID
Person on your LEFT (or Aisle)
Person on your RIGHT (or Aisle)
• PRINT YOUR NAME ON EACH PAGE!
THIS IS A CHM 234
• READ THE DIRECTIONS CAREFULLY!
PRACTICE EXAM
• USE BLANK PAGES AS SCRATCH PAPER
work on blank pages will not be graded...
MIDTERM #2
PRACTICE TEST #1
•WRITE CLEARLY!
• MOLECULAR MODELS ARE ALLOWED
• DO NOT USE RED INK
• DON'T CHEAT, USE COMMON SENSE!
Total (incl Extra)________/175+5
Extra Credit_____/5
H
He
Li Be
B
Na Mg
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
N
O
F
Ne
Al Si P
S
Cl
Ar
H/H
~1.0
Me/Me
~0.9
Kr
H/Me
~1.4
Et/Me
~0.95
In Sn Sb Te I
Xe
Me/Me
~2.6
i-Pr/Me
~1.1
Rn
Me/Et
~2.9
t-Bu/Me
~2.7
Tl Pb Bi Po At
H
C
H
N H
C
C
N
2850–2960
H
OR
1735
CH
11
220 O
10
200
R C OH
C CH3
–H2C NR2
C CH2
O
C
H
O
–OCH2–
Aromatic Ar H
mainly 8 - 6.5
7
140
6
120
5
100
R2C
CR2
C CH
4
80
3
60
RC
CR
1
1
20
0
0
Alkyl 3Y > 2Y > 1Y
C X
C NR2
Aromatic
Alkyl
3Y > 2Y > 1Y
2
40
–OCH2–
R C N
H
~15
C C
1500
NMR Correlation Charts
8
160
~2
H
NR2
1650
2000
H
H
C
1710
2500
9
180
~8
~2
C C
O
–H2C X
(δ, ppm)
H
~10
H
1600
O
2200
3000
O
C H
H
C C
C
amine R NH2 variable and condition
alcohol R OH dependent, ca. 2 - 6 δ
O
R C OH
~7
H
C
O
C O H
3500
H H
C C
1680
C
broad ~3000
(cm-1)
N
O
H
broad with spikes ~3300
broad ~3300
1600–1660
C
2200
O H
C
C
O
2720–2820
2 peaks
3000–
3100
Approximate Coupling
Constants, J (Hz), for
1H NMR Spectra
Infrared Correlation Chart
usually
strong
H
C
3300
Gauche
Eclipsing
Ga Ge As Se Br
O
C H
Interaction Energies, kcal/mol
-2-
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #1
NAME
Question 1 Give the IUPAC name for the following compounds. Be sure to use cis/trans, E/Z or
R/S where appropriate.
4
5
H
3
1
O
(3R)-propoxycyclopentene
CH2CH2CH3
2
Question 5 Sodium borohydride (NaBH4) reduces only aldehydes and ketones. Lithium aluminum
hydride (LiAlH4) will reduce aldehydes and ketones and also esters and carboxlic acids. Give a BRIEF
explanation for the different reactivities of NaBH4 and LiAlH4. Include the term "Lewis base" in your
explanation.
LiAlH4 is more reactive than NaBH4 because the electrons in the Al-H bonds are higher
in energy than those in the B-H bond, since Al is larger than B. LiAlH4 is thus the
stronger Lewis base, its reactive electrons are higher in energy
Question 4.
a) Give the organic reactant and the Grignard reagent you would use to make the
bond indicated by the dashed line in the provided structure (do not include the
aqueous acid workup step, stereochemistry is ignored in this question)
HO
Ph
MgBr
+
O
Ph
b) Give the organic reactant and the Grignard reagent you would use to make
the bond indicated by the dashed line in the provided structure (do not include
the aqueous acid workup step, stereochemistry is ignored in this question)
O
Me
MgBr
HO
+
Ph
Ph
c) Explain why the Grignard reaction shown would NOT work
Ph
Ph
MgBr
+
X
O
HO
the Grignard would have to attack the MOST substituted side of the epoxide, which
is slower than attacking the least substituted side
2
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #1 - 3 -
NAME
Question 5 For each reaction
1) Provide the missing reagents/conditions or major organic products as appropriate
2) State whether the OVERALL reaction is Addition, Elimination, Substitution or Rearrangement
3) Briefly explain whether the a solution of the product would be optically active or not
4) Pay attention to stereochemistry including racemic mixtures unless specified
O
CN
O
+
a)
heat
CN
CN
O
b)
H SN2
CN
OH H
Na+ –OCH3
–OCH
addition, chiral
reactants, single
enantiomer formed,
optically active
OCH3
CH3OH
addition, achiral
reactants, meso
product formed, not
optically active
3
the expected Walden inversion occurs
"pushes" the Me and H up
Br
substitution, achiral
reactants, achiral
product, not
optically active
NBS, hν
c)
d)
CH3
CH3
1. Hg(OAc)2, CH3OH
OCH3
2. NaBH4
neither
addition
not opically
active, achiral
Question 6. Provide the missing reactants for the following Diels-Alder reaction.
CN
+
heat
3
CN
(±)
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #1
-4-
NAME
Question 5. The purpose of this question is to determine whether the provided product is allowed
or forbidden
Δ
1) draw the arrow-pushing that describes formation of the PROVIDED product
2) How many electrons are involved in the reaction? 6 electrons
3) FOR THE PROVIDED PRODUCT (which may or may not be allowed), would
the ring closing be disrotatory or conrotatory? Conrotatory
4) FOR THE PROVIDED PRODUCT (which may or may not be allowed), would
the transition state be Hückel or Möbius? Möbius
5) Is PROVIDED PRODUCT allowed or forbidden and why?
Forbidden, the allowed product of a 6-electron electrocyclic ring closing
reaction would proceed via an aromatic Huckel transition state and
would be disrotatory, not Mobius/conrotatory
Question 6) For the following ion, draw all reasonable resonance contributors, draw an
"actual" structure that includes partial bonds and partial charges (use δ to indicate partial
charges), and draw the HOMO and LUMOs on TOP of the provided structures
δ
HOMO
and
resonance
δ
"actual" structure
the pi-molecular orbitals extend over the
conjugated part of the structures and does
not include any sp3 hybridized atoms
LUMO
Question 7. Show how you would synthesize the target compond on the right from the
starting compound on the left. Show reagents and conditions, and the structures of important
intermediate compounds. Do not show any (arrow pushing) mechanisms.
(±)
O
NBS/hν
Br
1. NaH
2. PrBr
NaOMe
1. BH3.THF
2. –OH/H2O2
(±)
OH
4
-5-
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #1
NAME
Question 8) Explain why the products of the following reaction are an alcohol and a bromide,
rather than two bromides, Draw a mechanism to support your reasoning
LA/BA
Br
H
O
OH
HBr
Br
+
LB/BB
OH2
LA/BA
H
Br
LB
H
LB/BB
O
Br
+
SN2
LA
can't do a
substitution at an
sp2 hybridized
carbon via either
SN1 or SN2, the
only possible further
reaction is loss of
proton to reform the
alcohol
Br
OH
X
these are the final products
Question 9). Give the curved arrow-pushing and the ALLOWED product of the following
cycloaddition reaction
CH3
CH3
A
N
H2C
+
CH2
CN
H2C
Δ
N
* *
4(s) + 2(s)
CH2
(±)
NC
CN
suprafacial/suprafacial allowed
B
NC
b) Give a pictorial representation of the
wavefunction of the HOMO ON TOP OF THE
STRUCTURE below for A, indicate the
number and positions of any vertical nodes
(ignore horizontal nodes)
CH3
HOMO
1 node
c) Give a pictorial representation of the
wavefunction of the LUMO ON TOP OF THE
STRUCTURE below for B, indicate the
number and positions of any vertical nodes
(ignore horizontal nodes)
CN
LUMO
NC
N
H2C
CH2
1 node
d) Give a brief justification for the stereochemistry in your allowed product, you must include
the following terms in your justification: suprafacial and/or antarafacial, HOMO, LUMO, bonding
and/or anti-bonding
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
trans- and are also trans- in the product
5
-2-
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #2
NAME
START OF PRACTICE TEST #2
Question 1 Give the IUPAC name for the following compound. Be sure to use cis/trans, E/Z or
R/S where appropriate.
NO2
1-bromo-2-ethyl-4-nitrobenzene
a)
Et
Br
O
b)
HO
2
1
3
4
6
4-methoxy-3-methylhex-(3Z)-en-1-ol
5
ethers are alway just "alkoxy" substituents
(alcohol highest priority functional group, determines
numbering)
Question 2. Give a complete curved arrow pushing mechanism, and...
1) Indicate the Lewis acid/Lewis base (LA, LB) at each step as appropriate, and whether they
are also Brønsted acids/bases (LA/BA, LB,BB)
2) GIVE THE NUMBER OF STEPS IN YOUR MECHANISM
HBr
OH
LB/BB
OMe
MeOH (solvent)
LB/BB
Me
H LA/BA
HO
O
H
Me
H
OH2
H
LA
O
O
Me
LA/BA
LB
Me
when dissolved in MeOH, HBr is essentially completely dissociated, just the same
as it is in H2O
4 steps
6
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #2 - 3 -
NAME
Question 3 For each reaction
1) Provide the missing reagents/conditions or major organic products as appropriate
2) State whether the OVERALL reaction is Addition, Elimination, Substitution or Rearrangement
3) Briefly explain whether the a solution of the product would be optically active or not
4) Pay attention to stereochemistry including racemic mixtures unless specified
a)
CF3
+
heat
F3C
(±)
OH
1. MCPBA
b)
addition, achiral reactants,
racemic mixture, not
optically active
(this is about as tricky a
Diels-Alder reaction I can
come up with!)
oxidation
not optically active,
racemic mixture formed
(±)
2. H3O+
OH
CN
Br
1 Equiv. Na+ –CN
c)
SN2 at allylic,
Br specifially benzylic
carbon is fast
H
O
Br
H
Na+ –OEt/EtOH
not protonated,
attack least
substituted side
d)
OH
substitution, chiral
reactants, single
enantiomer formed,
optically active
addition, chiral
reactants, single
enantiomer formed,
optically active
OEt
Question 4) The purpose of this question is to determine whether the provided product is allowed or
forbidden
CH3
CH3
N
Δ
CF3
H
F3C
N
H
F3C
CF3
H
H
1) draw the arrow-pushing that describes formation of the product
2) How many electrons are involved in the reaction? 4 electrons
3) FOR THE PROVIDED PRODUCT (which may or may not be allowed), would the ring
opening be disrotatory or conrotatory? Disrotatory
4) FOR THE PROVIDED PRODUCT (which may or may not be allowed), would the transition
state be Hückel or Möbius? Hückel
5) Is THE REACTION SHOWN allowed or forbidden, and why?
Forbidden, the allowed product of a 4-electron electrocyclic ring opening reaction would proceed via
a Mobius transition state and would be conrotatory, not Huckel and disrotatory
7
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #2
-4-
NAME
Question 4. Provide the missing reactants for the following Diels-Alder reaction.
CN
CN
(±)
+
CN
CN
Question 5. For the following structure:
a) Draw all additional reasonable resonance contributorts
b) Draw on TOP of the structure a pictorial representatrion of the wavefunction of both the
HOMO and the LUMO, give the number of vertical node (only) and indicate their positions.
N
N
N
N
N
resonance contributors
6 electrons in the π-system
node
node
N
N
node
node
node
N
N
N
LUMO
3 vertical nodes
HOMO
2 vertical nodes
Question 6. Rank the following structures in order of increasing rate of reaction in a DielsAlder reaction with fumaronitrile (shown), and give a brief explanation that includes the
terms "donating group", "withdrawing group", "energy of the electrons", "HOMO".
strong donating
withdrawing O
withdrawing O
CN
NH
NH
NH
strong donating
weak donating
weak donating B
A
B
A
C
––– < ––– < –––
NC
C
fumaronitrile
the dienes differ by the substituents that are circled, the energy of the electrons in the diene,
specifically those in the HOMO, are raised by donating groups and lowered by withdrawing
groups, raising the energy of the electrons in the HOMO decreases the HOMO/LUMO gap (the
LUMO on the fimaronitrile), which decreases the reaction activation energy and increases the rate
C has a strong donating group (non-bonding electrons on N) and a weak donating group (the alkyl
chain), it reacts fastest
A has a withdrawing and a strong donating group (non-bonding electron on the nitrogen), it is
intermediate
B has a withdrawing and only a weak donating group (the alkyl chain), it is slowest
8
-5-
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #2
NAME
Question 7. Show how you would synthesize the target componds on the right from the starting
compounds on the left. Show reagents and conditions, and the structures of important
intermediate compounds. Do not show any (arrow pushing) mechanisms.
Ph
Ph
Ph
Ph
O
NBS, hν
Br
Ph
Ph
Br
Ph
t-BuO–+K
Ph
Ph
1. BH3.THF
Ph
O–
Ph
Ph
2. H2O2/ –OH
+Na
Na H
OH
Question 7 (20 pts.)
a) Give the curved arrow-pushing and the ALLOWED product of the following cycloaddition.
State whether the product is achiral, a mso compound, a pure enntiomer or a racemic mixture
H3CO
A
CN
B
+
H3CO
heat
CN
H3CO
CN
(±)
(±) OR..
NC
CN
CN
b) Draw the HOMO for reactant A and the LUMO for reactant B on top of the structures below,
understanding that it may not be possible to get the geometry of the orbitals with respect to the
structures exactly correct because the structures have to be drawn flat on the paper
H3CO
CN
NC
LUMO
HOMO
c) does the allowed reaction proceed suprafacial/suprafacial or suprafacial/antarafacial?
suprafacial/suprafacial
9
-2-
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #3
NAME
START OF PRACTICE TEST #3
Question 1 Give the IUPAC name for the following compound. Be sure to use cis/trans, E/Z or
R/S where appropriate.
7
6
3
1
4
2
5
*
OEt
(6R)ethoxyhept-(2Z)-en-4-yn-2-ol
OH
Question 2. Give a complete curved arrow pushing mechanism, and...
1) Indicate the Lewis acid/Lewis base (LA, LB) at each step as appropriate, and whether they are
also Brønsted acids/bases (LA/BA, LB,BB)
2) GIVE THE NUMBER OF STEPS IN YOUR MECHANISM
LA/BA
O
H Cl
O
OH
OH
LB/BB
HCl cat.
O
LB
H
H
H
O
O
LB/BB
O
H
OH
LA/BA
LA
when dissolved in i-PrOH, HCl will be partially dissociated, an so it is not obvious
which acid species, HCl itself or protonated alcohol will be responsible for
protonation of the epoxide, you can use either, however, the i-PrOH solvent will be
present at MUCH higher concentrations than the conjugaye base anion from HCl,
and therefore deprotonation occurs to i-PrOH (even if the proton eventually gets
returned to form HCl)
10
CHEMISTRY 234, MIDTERM #3 PRACTICE TEST #3 - 3 -
NAME
Question 4 For each reaction
1) Provide the missing reagents/conditions or major organic products as appropriate
2) Pay attention to stereochemistry including racemic mixtures unless specified
3) State whether a solution of the product(s) would be optically active or not and give a brief
explanation
reaction at THIS alkene fastest because the
primary intermediate is a 3° cation
Br
achiral reactants,
1 Equiv. HBr
racemic product,
a)
not optically active
(±)
CO2CH3
heat
+
b)
CO2CH3
O
CO2Me
same
as
CO2Me
=
CO2Me
achiral reactants, meso product, not
optically active
must rotate to s-cis before reaction
OH
Na+ –OEt
c)
CO2Me
EtOH (solvent)
EtO
achiral reactants,
achiral product
formed, not optically
active
epoxide NOT protonated, attack
least substituted side
D Cl deuteriate here first, makes most stable intermdiate
D
D = deuterium = "labelled hydrogen"
DCl
(±)
(thermodynamic control conditions)
d)
achiral reactants,
racemic mixture,
not optically active
Cl
Question 5) Indicate which reaction is more exothermic, give an explanation
Br
H
Br
Br
B
HA
H
3 H atoms on the
C=C bond, 1
substituent, this
alkene is less
substituted, less
stable
H
only 1 H atom on
the C=C bond, 3
substituents, this
alkene is more
Br substituted,
more stable
the two alkene products are structural isomers, when comparing
structural isomeric alkenes the more substituted isomer is the
more stable (Sayetzeff/Zaitzeff etc.) rule, formation of the more
stable isomer is more exothermic, reaction B is more exothermic
than reaction A
11
CHEMISTRY 234, MIDTERM #3 PRACTICE TEST #3
-4-
NAME
Question 5. Show how you would synthesize the target componds on the right from the starting
compounds on the left. Show reagents and conditions, and the structures of important
intermediate compounds. Do not show any (arrow pushing) mechanisms.
H
ignore
stereochemistry
here
HO
O
O
H
O
NBS, hν
1. Hg(OAc)2/H2O
2. NaBH4
Br
O
H
O
O
O
t-BuO–+K
O
H
Δ
O
Question 6) The ylide below undergoes an electrocyclic ring closure reaction
t-Bu
S
Δ
t-Bu
S
t-Bu
*
*
H
H
meso compound
t-Bu
a) give the curved arrow-pushing that accounts for product formation
b) draw the product, paying special attention to relative stereochemistry of any substituents
*
c) indicate the locations of any chiral (asymmetric) carbons atoms
with the symbol, and
state whether it is racemic, a meso compound or achiral
*
d) give the NUMBER of electrons involved in the reaction
4
e) state whether the allowed reaction proceeds via a Huckel or a Mobius transition state
Mobius
f) state whether the allowed reaction proceeds via a conrotatory or a disrotatory ring
closing
conrotatory
g) Draw a pictorial representation of the HOMO on top of the structure below, give the
number of vertical nodes (only) and oindicate their positions
1 node
t-Bu
S
t-Bu
12
-5-
CHEMISTRY 234, MIDTERM #3 PRACTICE TEST #3
NAME
Question 7. a) Give a full curved-arrow pushing mechanism for formation of both products of
the provided reaction. One of these products would be formed preferentially under conditions
of kinetic control, the other preferentially under conditions of thermodynamic control, indicate
which is which. Indicate the Lewis acid and base at each step and whether they are also
Bronsted acids/bases.
kinetic
thermodynamic
OCH3
Br
CH3OH
H3CO
B
+
A
heat
CH3
H O
CH3
LB/BB H O
H
LA/BA
O
H3C
H
O CH3
H3C
O H
H LB/BB
O CH
3
LA/BA
b) Give a reaction energy diagram for both reactions in the SAME DIAGRAM
‡
thermodynamic
‡
kinetic H3C
O H
energy
‡
both
Br
‡
‡
CH3OH
H
O
H3C
kinetic
OCH3
H3CO
thermodynamic
reaction coordinate
c) Give a brief explanation of how temperature is related to kinetic and thermodynamic control
at all temperatures the kinetic product is formed faster, at lower temperatures the reactions will be
more IRREVERSIBLE, the kinetic product product will predominate, at higher temperatures the
reactions will become more REVERSIBLE and the lower energy thermodynamic product can be
formed and will start to accumulate
13
CHEMISTRY 234, MIDTERM #3 PRACTICE TEST #3 - 6 -
NAME
Question 8. The purpose of this question is to determine whether the provided product of the
cycloaddition reaction given below is allowed or forbidden (there are several possible products
of this reaction, we will focus our attention on this one to see if it is allowed)
a) give the curved arrow-pushing that accounts for product formation
b) draw the HOMO and LUMO ON TOP OF THE structures as indicated above, and give the
number of vertical nodes and clearly indicate their positions
c) IGNORING THE PROVIDED product for now, use the information from the F.M.O.s to
decide whether the ALLOWED reaction would be suprafacial/suprafacial or suprafacial/
antarafacial
suprafacial/antarafacial
your answer________________________________
d) Using the sterochemistry of the PROVIDED PRODUCT, decide state whether the it was
formed via suprafacial/suprafacial or suprafacial/ antarafacial cycloaddition
suprafacial/antarafacial
your answer________________________________
d) state whether the PROVIDED PRODUCT is allowed or forbidden, and give a BRIEF
explanation that mentions the frontier molecular orbitals.
1 node
1 node
suprafacial on this reactant (shown with
both bonds being made to the bottom of the
carbon atoms)
HOMO
CN
+
Δ
(±) TRANS
CN
LUMO
antarafacial on this reactant (shown with
one bond being made to the top of one
carbon atom and one bond being made to
1 node
the bottom of the other carbon atom)
The provided product is ALLOWED, it is formed in suprafacial/antarafacial reaction
and the phases of the HOMO and LUMO at the relevant carbons result in two
bonding interactions for such a reaction
the reaction is antarafacial on the lower reactant because the cis-stereochemistry of the
substituents becomes trans- in the product (this would not be included as part of the answer)
Question 9) Classify the following structures as aromatic, non-aromatic or anti-aromatic, assume
all structures are as flat as possible, AND give the number of electrons involved in the conjugated
system
NC
CIS-
CN
sp3
4 electrons
non-aromatic
4 electrons
anti-aromatic
N
these electrons are
in sp2 hybrid A.O.
8 electrons
8 electrons
anti-aromatic
anti-aromatic
14
-2-
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #4
NAME
START OF PRACTICE TEST #4
Question 1. Provide TWO Grignard reactions, A and B, that can be used to make the
provided target structure. Give the organic reactant and the Grignard reagent that
would be used, you do not need to specify the aqueous acid workup step, but you
musty specify which of the C-C bonds is being made in the provided target structure.
OH
O
MgBr
A)
+
H
OH
O
H
B)
+
BrMg
OH
O
BrMg CH3
+
OR...
Question 2) Rank the following in order of icreasing rate of reaction in a base catalyzed
hydrolysis reaction (addition of water in the presence of hydroxide) and give a brief explanation
(hint, think abouyt the slowest, rate determining step for base catalyzed hydrolysis)
Me
O
Me
Me
slow
Me
O
H
Me
A
OH
Me
slowish!!
H
B
D
–––
<
A
–––
OH
<
O
H
H
B
–––
C
C
< –––
H
i-Pr
fastest
H
i-Pr
O
i-Pr
slowest
i-Pr
D
OH
OH
The rate determining step is hydroxide as Lewis base in SN2 type attack on carbon
of the Lewis acid epoxide. This process is subject to steric hinderance, hence the
order given.
Question 3 Show how you would synthesize the target componds on the right from the starting
compounds on the left. Show reagents and conditions, and the structures of important intermediate
compounds. Do not show any (arrow pushing) mechanisms.
CH3 CH2OH
CH3 CH2
CH2
CH2OH
O
1.
PBr3
2. H3O+
CH3 CH2Br
Mg.THF
CH3 CH2MgBr
15
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #4 - 3 -
NAME
Question 4. For each reaction.
1) Provide the missing reagents/conditions or major organic products as appropriate
2) Pay attention to stereochemistry including racemic mixtures unless specified
OH
1. MCPBA
a)
2. MeOH/HCl (cat.)
OMe
(ignore stereochemistry)
H3C
H3C
CN
b)
heat
+
(±)
CN
c)
EtMgBr
Br
HO
1. MCPBA
d)
2. H2O/HCl(cat.)
OH
not a racemic
mixture, meso
compound
Question 5) a) Give the curved arrow pushing and the product of the following reaction. Pay
attention to stereochemistry and state whether a solution of the product(s) would be opticlly active or
not.
CH3
H
CH3
H3C
CH3
C
racemic mixture
heat
C
A
+
formed, not
B
(±)
N
optically
active
C
N
H
H3C
CH3
O
O
For BOTH of the reactants A and B:
b) Give a pictorial representation of the requested frontier molecular orbital as requested on top of
the provided structure
c) Give the number of electrons in the conjugated system that are relevant to the reaction
d) State whether the allowed reaction is suprafacial or antarafacial
H
H3C
A: HOMO
O
N
C
CH3
B: LUMO
C
C
H
CH3
2 electrons
suprafacial
4 electrons
suprafacial
16
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #4
-4-
NAME
Question 6. Show how you would synthesize the target compound on the right from the starting
compound on the left. Show reagents and conditions, and the structures of important intermediate
compounds. Do not show any (arrow pushing) mechanisms.
(ignore stereochemistry)
NBS/hν
O
1. NaH
2. PrBr
O
Br
1.
H
Mg.THF
2. H3O+
MgBr
OH
Question 7. Consider the energy of an electron in each of the following π-molecular
orbitals AND a p atomic orbital on a carbon atom and rank them in order of
increasing energy. Two of the energies will be essentially equal, as indicated below
essentially same
as non-bonding
A
C
E
F (p atomic non-bonding by
orbital)
definition
B
most anti-bonding
interactions
D
most bonding interactions
D < A < C ~ F < E < B
––– ––– ––– ––– ––– –––
highest
lowest
roughly
energy
energy
the
same
17
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #4
-5-
NAME
Question 8) Rank the following reactions, A, B and C, in order of INCREASING
exothermicity. Give a BRIEF explanation
2 H2
A
A
<
lowest
exothermicity
2 H2
B
C
B
highest
exothermicity
<
2 H2
C
the products are all the same, the energies at the end of all reactions is thus the same, the
difference is in the reactants. A and C are conjugated, electrons are lower in energy, the
reactants in A and C start lower in energy, thus less exothermic than B, the diene is more
substituted in A compared to C, diene A is thus more stable, lower in energy, reaction A is
least exothermic
Question 9) The structure below undergoes an electrocyclic ring opening reaction
(remember, D means deuterium, an isotope of hydrogen that is often used as a
labelled hydrogen atom)
D
Δ
D
D
D
a) give the curved arrow-pushing that accounts for product formation
b) draw the product, paying special attention to relative stereochemistry of any substituents
c) give the NUMBER of electrons involved in the reaction 6
d) state whether the allowed reaction proceeds via a Huckel or a Mobius transition state Huckel
e) state whether the allowed reaction proceeds via a conrotatory or a disrotatory ring closing
disrotatory
Question 10. Provide the missing reactants for the following Diels-Alder reaction.
CN
+
heat
(±)
CN
18
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #4 - 6 -
NAME
Question 12) Provide a detailed (arrow pushing) mechanisms for the following
transformations. draw all important resonance structures. For each intermolecular step,
identify the Lewis acid and base (LA/LB) as appropriate, and whether they are also Bronsted
acids/bases (BA/BB), give the number of steps in your mechanism (hint BOTH SN1 and SN2
can occur at allylic carbon atoms)
H
LB/BB
conc. HBr
Ph
O
Br LA/BA
OH +
heat
Ph
O
Ph
Br
+
Ph
Ph
LA
Br
OH
H
LB
this problem is slightly tricky, substitution here is SN1, the choice between SN1 and SN2 in simpler
cases is the usual one, you can't do SN2 on a tertiary carbon and you can't do SN1 on a primary
carbon, secondary is always a bit ambiguous, as is allylic, because both SN2 and SN1 are favored
at this positions, HOWEVER, this is a mechanism problem, and in this case I gave you the product
and you can see that the substitution can't have been Sn2 because the -Br is not on the original
carbon that had the leaving group, so in this case it had to be SN1
Question 13. Show how you would synthesize the target compond on the right from the starting
compound on the left. Show reagents and conditions, and the structures of important intermediate
compounds. Do not show any (arrow pushing) mechanisms.
OH
a)
O
Br2/hν
Na2Cr2O7/H2SO4/H2O
MgBr O
1.
Br Mg.THF
OH
2. H3O+
OH
O
b)
Ph
Ph
PCC/CH2Cl2
the last 2 steps
can also be shown as one reaction
with the 1. 2. notation
O
O– +Na
OH
Ph
1. EtMgBr
2. H3O+
Ph
Br
NaH
19
Ph
Question 6. Show how you would synthesize the target componds on the right from the starting
compounds on the left. Show reagents and conditions, and the structures of important
intermediate compounds. Do not show any (arrow pushing) mechanisms.
OH
OH
a)
PCC/CH2Cl2
O
1. MeMgBr
2. H3O+
OH
b)
MCPBA
Ph
O
1. PhMgBr
2. H3O+
O
OH
c)
PBr3
PCC
OH
Br
MgBr
Mg.THF
1.
H
2. H
O
Ph
O+
3
Question 3. For each reaction.
1) Provide the missing reagents/conditions or major organicproducts as appropriate
2) Pay attention to stereochemistry including racemic mixtures unless specified
O
MgBr
a)
1.
(±)
Ph
OH
2. H3O+
1. PBr3
OH
b)
D
2. Mg.THF
3. D2O
O
c)
O
OH
1. Excess CH3MgBr
OH
2. H3
O+
20