Third Midterm Practice Exams - Organic Chemistry at Arizona State

Transcription

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 #3
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
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, MIDTERM #3 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.
H
6
trans-(5R)-hydroxyhex-(3)-enal
O
OH
*R
OR
5
3
4
2
1
H
(5R)-hydroxyhex-(3E)-enal
aldehyde not numbered, is in position #1 by definition
Question 2 Rank in order of increasing equilibrium constant for formation of an acetal with
a brief explanation. Draw the expected acetal for one of the reactions (only), it does not
matter which one.
MeOH
O
A
H
H+ (cat.)
MeOH
O
B
OMe
acetal
H
MeO
MeO
OMe
acetal
MeO
OMe
B
<
A
lowest
<
C
highest
H+ (cat.)
MeOH
O
C
H
F
H+ (cat.)
F
acetal
H
F
F
MeOH is a weak L Base, reactivity of carbonyls (C=O) with Lewis bases depends upon
substituents effects on the carbonyl carbon, B has two weakly donating alkyl groups attached to
the carbon of the C=O and is thus the least reactive and has the smallest equilibrium constant, C
has 2 F atoms that inductively withdraw electrons and increase reactivity and equilibrium constant
Question 3 Give the alkyl bromide and the carbonyl compound you would use to
synthesize the following alkene in a Wittig synthesis and show all steps and
reagents/conditions
Br
PPh3
Ph
1° bromide preferred
BuLi
PH3P
Ph
PH3P
Ph
+
O
Ph
CHEMISTRY 234, MIDTERM #3 PRACTICE TEST #1 - 3 -
NAME
Question 4 For each reaction
a) Provide the missing reagents/conditions or major organic products as appropriate, pay
attention to stereochemistry including racemic mixtures unless specified
b) Unless otherwise indicated.....
State whether the OVERALL reaction is Addition, Elimination, Substitution or Rearrangement
State whether the reaction is oxidation, reduction or neither
Briefly explain whether the a solution of the product would be optically active or not
H
O
H
Zn(Hg)
a)
*
*
HCl, H2O
SUBSTITUTION (of 2xO for 2xH)
REDUCTION
not optically active
achioral meso compound
H
H
O
O
1 Equiv. (CH3)2NH
b)
H
HO
NMe2
O
HCl (cat.)
ignore stereochemistry/optical activity
ignore oxidation/reduction
ignore addition/elimination etc
O
Na2Cr2O7/H2SO4
c)
OH ignore stereochemistry/optical activity
ignore addition/elimination etc.
O
OXIDATION
O
O
CO/HCl
d)
O
O O
O
AlCl3
H
e)
OH
ignore oxidation/reduction etc.
H3O+
OH
ignore oxidation/reduction
ignore addition/elimination etc
OHC SUBSTITUTION
O
OH
-4-
NAME
Question 5 Draw the complete arrow pushing mechanism for the following reaction.
Indicate the Lewis acid/base at each step, and if they are also Brønsted acids bases. Add
non-bonding electrons as necessary. Draw the ALL important resonance structure of the
intermediates
H3N
LB
NH
O
NH3
LA
TsOH (cat.)
H3N
LB/BB
H
H2N
LB/BB H3N
O
LA/BA
H OTs
LA/BA
H2N
O
H NH
LA/BA
H N
H
LA/BA
TsO H
LB/BB
H2N
H2N
OH LB/BB
OH2
note: the order of the first 2 steps in mechanism a) could be reversed!
Question 6 Rank the following in terms of increasing rate of reaction with
PhMgBr. Give a BRIEF explanation and NAME the three functional groups
WD = weakly donating
SD = strongly donating
O
WD
A
ketone
WD
O
O
SD B
ester
WD
aldehyde
O
WD C
H
B
–––
A < –––
C
< –––
this is reaction of a strong nucleophile/LB with a carbonyl C=O bond, which can be considered to
be a small π-system, the carbonyl carbon in the ester B has a strong electron donating oxygen
substituent on the carbonyl and a weak electrom donating methyl group, which decreases
reactivity towards the LB/nucleophile, the ketone A has 2 weak alkyl donating substituents on the
carbonyl carbon, the aldehyde C has only 1 weak alkyl donating group
-5-
NAME
Question 7 Show how you would make the target molecules from the provided
starting structures. Show all intermediate structures, do not show any mechanisms
CO2H
CH3
Br
a)
NO2
1. KMnO4 / –OH / heat
HNO3 / H2SO4
2. H3O+
CH3
CH3
Br
Br2 / FeBr3
separate
isomers
NO2
NO2
O
O
OH
b)
PBr3
O
Br
Na/NH3(l)
HO OH
HCl cat.
Na+
O
O
Br
O
O
H3O+ O
recall, H3O+ does not react with alkynes without Hg2+ as a catalyst
Question 2. For the Bronsted acid/base reaction below:
a) Give the curved arrow-pushing in both directions
b) Draw a reaction energy diagram and include a drawing of the transition state
c) Label the acids/bases and which are stronger and give a brief explanation
d) Indicate which reaction is faster (left to right or vica versa) and on which side the
equilibrium lies and which acid has the smaller and which the larger pKa
H
+
H
slower
H
H
faster
H
weaker base
weaker acid
larger pKa
equilibrium on THIS side
+
stronger acid
smaller pKa
H
stronger base
‡
energy
H
‡
H
H
reaction coordinate
the weaker base has lower energy electrons because the ion is aromatic, the stronger base
is anti-aromatic if flat, or it it twists it may become non-aromatic, but will be less stable than
the aromatic anion in any geometry
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
CHEMISTRY 234, MIDTERM #3
PRACTICE TEST #2
-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
7
3
6
2
1 H
5-hydroxy-4-methylhept-(4E)-en-6-ynal
5 4
O
OH
Question 2 Rank the following in terms of increasing rate of electrophilic
aromatic substitution, e.g., reaction with HNO3/H2SO4. Give a BRIEF explanation
O
O
W O
O W
D A
O
O
O
D
W O
O
O
D
D B D
D
O
D
D C D
O
A
–––
B < C–––
< –––
the reaction is electrophilic aromatic substitution, as far as the central benzene rings are
concerned, A has 2 D/activating groups and 2 W/deactivating groups, B has 3 D/activating
groups and 1 W/deactivating group, C has 4 D/activating groups, C is thus fastest in
electrophilic aromatic substitution
Question 3 Give the product of complet acid catalyzed hydrolysis of the
following structure
N
O
H3O+
O
HO
N
H
add C=O here
cleave the 2 single bonds indicated by the dashed lines
H
NAME
a) Provide the missing reagents/conditions or major organic products as appropriate, pay
attention to stereochemistry including racemic mixtures unless specified
O
1. Ph-MgBr
a)
N
C
2. H3O+
O
AlCl3
1. Cl
b)
MeO
2. Zn/Hg/HCl/H2O
MeO
HO
O
c)
H
CH3OH
CH3O–
O
d)
H
OCH3
(±)
hemiacetal formed with base
(CH3)2NH
NMe2
CF3CO2H (TFA) cat.
(or any other organic acid catalyst)
e)
1. BuLi
2. CH3Br
3. BuLi
S
H
S
H
4. PhCH2Br
5. H3O+
O
PhCH2
CH3
-4-
NAME
Question 5 Give a full curved arrow-pushing mechanism for the following reactions, show
where every proton goes to and comes from (no +H+/-H+) and indicate the Lewis and
Bronsted acids/bases at each intermolecular step, include important resonance
contributors for all intermediates, give the number of steps in your mechanism.
H
O
O
H
O
O
H
HO
HCl/H2O
a)
OH
OH
LA/BA
LB/BB
H
H
OH
O
LB/BB
H
O
LA/BA
O H
H
LA
O
OH
O
OH
O
OH
OH
H
H
O
OH
LB
LA/BA O
H
H
LA/BA
H
O
H
LA/BA
OH
H
H LB/BB
OH LB/BB
NaOH/H2O
O
O
LB/BB
O
O
SEVEN steps
b)
O
O
O
H
H
LA/BA
OH
OH
-4-
NAME
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.
HO
a)
O
1.
2. H3O+
Br2, hν
Br
BrMg
Mg . THF
O
OH
a)
OH
NaBH4/EtOH
/ H+ cat. (not H3O+)
HO
O
OH
O
O
OH
HBr/ROOR
O
O
O
Mg.THF
O
O
1.
2. H3O+
Br
MgBr
Question 6) The ylide below undergoes an electrocyclic ring closure reaction
t-Bu
S
Δ
t-Bu
t-Bu
S
*
t-Bu
*
H
H
meso compound
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
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
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
-2-
NAME
R
7
8
6
5
OH
O
*
4
2
3
(4R)-hydroxyoct-(6Z)-en-2-one
1
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), show where every proton comes from and
goes to (no +H+/-H+)
2) GIVE THE NUMBER OF STEPS IN YOUR MECHANISM
Cl–H
O
O
HCl
O
O
OH
HO
H O
H O
O
O
HO
H
HO
O
H O
O
O
–Cl
OH
HO
FOUR steps
Question 3) 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
sp3
6 electrons
O
H
non-aromatic
H
N
N
aromatic
6 electrons
these electrons
are in sp2
hybrid A.O.s
aromatic
6 electrons
NAME
1) Provide the missing reagents/conditions or major organic products as appropriate
N
a)
O
H3O+
Ph
Ph
H3N
CHO
H
H
N
CO/HCl
b)
Br
H
H
N
and/or
AlCl3
Br
H
N
Br
OHC
Ph
Ph
H3O+
OMgBr
c)
O
O
OH
O
1. PPh3
Br
d)
2. BuLi
3. O
O
1 Equiv.
HO
e)
H
O
ignore stereochemistry
TsOH (cat.)
OH
O
O
H
O
-4-
NAME
Question 4 Rank the following in terms of increasing frequency of carbonyl stretching vibration
in an IR spectrum. To solve this problem you will ened to draw minor resonance contributors
and remember that stronger bonds vibrate with higher frequency)
O
the more the minor resonance
structure contributes to the overall
H
structure, the more the C=O bond H3C
has single bond character, the
A
lower the vibrational frequency....
O
H3C
H3C
H
H is not a donor, does not
stabilize the minor resonance
structure which is thus a small
contributor to the structure
O
H3C
NMe2
H3C
C
B
A
< –––
C
< –––
B
–––
O
O
H H3C
O
O
NMe2
H3C
O
NMe2
H3C
-NMe2 is the strongest donor, it
stabilizes the minor structure
resulting in a largest contribution to
the structure of these three
O
CH3
-CH=CH2 is a weak
donor, it is in the middle
Question 5 Give the product of the following reaction. Remember that D represents deuterium,
an isotope of hydrogen, that is used to keep track of where hydrogen atoms go in chemical
reactions. We did not cover this reaction class, but you should be able to work it out based on
what you know about the mechanisms of these reduction reactions
H
N
C
H3C
D
1. LiAlH4
CH3
H
N
H C
CH3
H3C
2. D3O+
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
D
Δ
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
-5-
NAME
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.
CO2H
a)
Br
SO3H
KMnO4
boil
Br2
FeBr3
CO2H
CO2H
SO3
H2SO4
SO3H
O
OH
b)
Br
H2/Pd/C
HO
O
O
HO OH
HCl cat.
HO
Br
O
O
O
Mg.THF
BrMg
BrMgO
O
O
H3O+
O
NAME
H
O
H
H
H
HO
H3O+
O
+
O
C
a)
H
HO
O
H
O
H
H O
O CH2
H
O
H
O
H
H
O
H
H
O
H
O
O
+
H
O
H
HO
H
H
O
H
O
O
HO
HO
O CH2
H
O
H
O
O
H
O
O
H
H
O
H
cytosine is one of the pyrimidine bases in DNA, it can be converted into uracil. if this happens
this can be a damage mechanism that could lead to mutation. Assume that this reaction
occurs via the usual acid catalyzed mechanisms that we study in class, give a mechanism for
formation of uracil from teh provided tautomer of cytosine
H
O+
H
H
N
H
b)
N
N
H
O
H
H
O
N
N
N
H
H
O
H
H
cytosine
tautomer
O
H
H
H O
H H
H N
O H
H
N
O
N
H
uracil
H3O+
H
H
O+
N
H
O
H
H
H N
H
N
O
N
H O
H
OH
N
H
H3N
H
N
O
OH
N
H
O
H
O
N
N
H
H
H
-2-
NAME
3
6
4
5
2
1
H
3-butyl-4-methyl-5-oxo-hex-(3E)-enal
O
O
Question 2 Rank the following in order of increasing equilibrium constant for formation of a
hydrate. Give a BRIEF explanation
O
O
O δδ+
B
C < –––
< –––
A
–––
H3CO
A
O2N
B
C
the reaction is addition of a weak nucleophile to the C=O group, A is least reactive since it
has a strong donating group that can stabilize the carbonyl carbon via resonance, B has a
withdrawing group that destabilizes the carbonyl carbon
Question 3. Rank in order of increasing rate of reaction with –CN, give a BRIEF explanation
O
O
O
O
A
(fastest)
C
<
A
F
F
B
C
<
B
(slowest)
B has donating group (oxygen) adjacent to the C=O, decreases reactivity towards
nucleophilic attack, C has two electronegative groups adjacent to the C=O, inceasing
reactivity towards nucleophilic attack
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
NH2
a)
N
O
O
O
HCl (cat.)
H
O
Br
N2H4
b)
HO
KOH/heat
Br2 / FeBr
c)
F3C
Br
F3C
O
d)
(CH3)2NH
N
enamine
H+ cat.
OH
e)
O
H3O+
O
OH
-4-
NAME
Question 5. 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.
Br
a)
Cl
O
NH2
/ AlCl3
O
Cl
Cl2 / AlClr3
HNO3 / H2SO4
O
NO2
bit of a trick here, the Clemmensen reduction
would probably also reduce the -NO2 to the
required -NH2 making the next step (H2/Pd/C)
unnecessary, but you would not lose points for
the separate reduction of the -NO2
Zn(Hg)/HCl/H2O
Br
H2/Pd/C
Br2 / FeBr3
separate
isomers
NH2
NO2
O
b)
NH2
HO
H
H
N
O
1 Equiv
HCl
cat.
CH3NH2
HCl (cat.)
OH OH
O
H
O
1. PhMgBr
O
HO
H
2. H3O+
O
Ph
Ph
-5-
NAME
H
H
O
H
O
a)
O
H3O+
O
H
H
O
H
O
HO
H
H
O
+
OH
HO
H
OH
O
O
O
HO
H
H HO
O
O
OH
O
HO
HO
O
H
H
O
OH
O
H
H
H3O+
••
O
b)
O+
H
O
O
H
H
H
H
O
+
+
H
H
H
H
H
•• O
O ••
H
+
O
H
H
O+
H
O
H
H
+
H
O
H
H
NAME
Question 7 Rank in order of increasing rate of reaction with a Grignard reagent, giove a brief
explanation in terms of nucleophiles and electrophile stregth and tthe factors that control these
in this context.
O
O
H
H
H3C
O
H
A
D
–––
H
F3C
B
O
H3C
C
A < –––
B
< –––
CH3
D
C
–––
<
In these reactions the Grignard is the Lewis base and the carbonyls are the Lewis
acid, the stronger the Lewis acid the faster the reaction
the carbonyl carbon in D has two weak donating -CH3 groups attached, which
decerases the electrophilicity, this reaction is slower than A (one donating group)
which is slower than B (zero donating groups)
C is fastest of all, the -CF3 is electron withdrawing, which incerases the
electrophilicity of the carbonyl carbon
Question 8. Rank in order of increasing rate of electrophilic aromatic substitution at the
carbons indicated by the arrows. Give a BRIEF explanation.
B
A
H
D
N
C
C
CH3
D
slowest
<
B
<
C
N
<
A
fastest
Reaction at both A and C is faster than at B and D, because both are activated by strong (amine)
and weak (aryl) donating groups on the ring. Reaction at A is activated more than at C because
the strongest donating group activates more. Reaction at B and D is deactivated by the by strongly
withdrawing nitrile group, but D is deactivated more than at C.

Third Midterm Practice Exams - Organic Chemistry at Arizona State

Transcription

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