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Chemistry 3719, Fall 2012 Exam 1 Name: Student number: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck.
1. (8 pts) Draw structures for all of the cycloalkane isomers with the formula C5H10, and then give each of your structures an acceptable name.
2
2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or common names for substituents.
OH
Cl
a.
b.
c.
OH
3. (8 pts) Fill in the ground state electron distribution for O (from the periodic table), and then construct hybrid
orbital pictures for the highlighted O atoms that describe the orbitals used for bonding in each case.
Energy
H3C OH
HC O
hybr idize
ground state O H
Explain briefly why hybrid orbitals are necessary here:
3
4. (12 pts) Give the products expected from each of the following acid-base reactions. Then label each acid with an approximate pKa and indicate whether products, reactants, or neither are favoured in each case.
+ CH3CH2OKa.
b.
c.
CO2H
CC
H
+ LiN[CH(CH3)2]
OH
+ CH3ONa
5. (8 pts) Provide a complete mechanism for the following reaction that includes curved arrows to denote the making and breaking of bonds. Indicate the rate-determining step for this process.
4
6. (6 pts) Complete the following structures by adding any needed formal charges.
7. (6 pts) Draw a second resonance structure and an overall hybrid for each of the following species.
a.
b.
c.
H3C
O
O
CH3
O
CH2
HC N N
H
8. (6 pts) Show the oxidation number for each C atom in the following reactant and product, and then indicate whether each C atom is oxidized, reduced, or neither in the reaction.
5
9. (10 pts) Draw two chair conformations for cis-1-t-butyl-3-methylcyclohexane that are related through a ring-flip. Then circle which conformation you expect to be more stable and explain why. Then do the same for the trans isomer and, finally, indicate whether the cis or trans isomer should be more stable overall and explain your choice.
10. (9 pts) Draw Newman depictions that correspond to the following conformations. a. The least stable conformation of 3-methylnonane along the C-4–C-5 bond.
b. The most stable conformation of 1,1-dibromo-6-chlorohexane along the C-3–C-4 bond.
c. A gauche conformation for 5-methyl-2-heptanol along the C-3–C-4 bond.
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11. (9 pts) Rank the following species as indicated: a. Lowest to highest electronegativity (1 = lowest, 5 = highest)
b. Lowest to highest pKa (1 = lowest, 5 = highest)
c. Lowest to highest boiling point (1 = lowest, 5 = highest)
12. (9 pts) Within each pair of molecules below, indicate which is more stable and then give a brief explanation
for your choices in each case.
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Chemistry 3719, Fall 2012 Exam 1 - Key Name: Student number: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck.
1. (8 pts) Draw structures for all of the cycloalkane isomers with the formula C5H10, and then give each of your structures an acceptable name.
CH3
CH3
CH3
CH3
CH3
cyclopentane
methylcyclobutane
cis-1,2-dimethylcyclopropane
trans-1,2-dimethylcyclopropane
H3C CH3
1,1-dimethylcyclopropane
CH2CH3
ethylcyclopropane
2
2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or common names for substituents.
3. (8 pts) Fill in the ground state electron distribution for O (from the periodic table), and then construct hybrid
orbital pictures for the highlighted O atoms that describe the orbitals used for bonding in each case.
Energy
H3C OH
HC O
hybr idize
ground state O H
sp3 sp2p
Explain briefly why hybrid orbitals are necessary here: The most obvious reason is that the lone pairs in the ground state structure are not equivalent; the hybridization model fixes that.
3
4. (12 pts) Give the products expected from each of the following acid-base reactions. Then label each acid with an approximate pKa and indicate whether products, reactants, or neither are favoured in each case.
+ CH3CH2OKa.
b.
c.
CO2H
CC
H
+ LiN[CH(CH3)2]
OH
+ CH3ONa
+ CH3CH2OH
CO2K
CC
Li
+ HN[CH(CH3)2]
ONa
+ CH3OH
pKa ~ 5 pKa ~ 16products favoured
pKa ~ 26 pKa ~ 26products favoured
pKa ~ 16 pKa ~ 16neither favoured
5. (8 pts) Provide a complete mechanism for the following reaction that includes curved arrows to denote the making and breaking of bonds. Indicate the rate-determining step for this process.
C
CH3
CH3
CH3CH2 OH C
CH3
CH3
CH3CH2 BrH Br
+ H2O
C
CH3
CH3
CH3CH2 OH2 C
CH3
CH3
CH3CH2Br
Br
rate-determining
4
6. (6 pts) Complete the following structures by adding any needed formal charges.
a. b.C O N
H
H
H O H O N
O
O
c. O C
O
S
7. (6 pts) Draw a second resonance structure and an overall hybrid for each of the following species.
a.
b.
c.
H3C
O
O
CH3
O
CH2
HC N N
H
H3C
O
O
CH3
O
CH2
HC N N
H
H3C
O
O
HC N N
H
CH3
O
CH2
8. (6 pts) Show the oxidation number for each C atom in the following reactant and product, and then indicate whether each C atom is oxidized, reduced, or neither in the reaction.
5
9. (10 pts) Draw two chair conformations for cis-1-t-butyl-3-methylcyclohexane that are related through a ring-flip. Then circle which conformation you expect to be more stable and explain why. Then do the same for the trans isomer and, finally, indicate whether the cis or trans isomer should be more stable overall and explain your choice.
C
CH3
CH3
CH3H3C
CCH3
H3C CH3
CH3
H H
H
H
C
CH3
CH3
CH3H
CH
H3C CH3
CH3
CH3 H
H
H3C
Lots of 1,3-diaxialinteractions which
make this chair formless stable
both large groups are equatorial, nosignificant 1,3-diaxial interactions
cis isomer
trans isomer
Larger group axial sosignificant 1,3-diaxialinteractions that willdestabilize this form
larger group equatorial thereforeminimizing 1,3-diaxial problems cis isomer more stable overall since both groups are
able to be equatorial minimizing 1,3-diaxial problems
10. (9 pts) Draw Newman depictions that correspond to the following conformations.
a. The least stable conformation of 3-methylnonane along the C-4–C-5 bond.
b. The most stable conformation of 1,1-dibromo-6-chlorohexane along the C-3–C-4 bond.
c. A gauche conformation for 5-methyl-2-heptanol along the C-3–C-4 bond.
6
11. (9 pts) Rank the following species as indicated: a. Lowest to highest electronegativity (1 = lowest, 5 = highest)
3 5 4 1 2
b. Lowest to highest pKa (1 = lowest, 5 = highest)
2 4 1 3 5
c. Lowest to highest boiling point (1 = lowest, 5 = highest)
3 1 4 2 5
12. (9 pts) Within each pair of molecules below, indicate which is more stable and then give a brief explanation
for your choices in each case.
a.
b.
c.
ONa ONa
vs.
BrBr
BrBr
vs.
OLi NHLi
vs.
Charge delocalized in phenoxide ion therefore morestable than the localized charge in the alkoxide ion
Both large groups are able to be equatorial in thisisomer thereby avoiding 1,3-diaxial interactions
Charge is situated on the more electronegative Oatom and therefore more stabilized than on N
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Chemistry 3719, Fall 2012 Exam 2 Name: Student number: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck.
1. (9 pts) Within each of the following pairs of molecules, indicate which will react at a faster rate in the given reaction; then give a brief explanation for your choice in each case.
a.
b.
c.
CH3
H3C H
CH3or in electrophilic addition
BrH H
BrD D
or in E2 elimination
OH OHor in SN2 substitution
2
2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or common names for substituents.
3. (8 pts) Provide a detailed mechanism for the following transformation that uses curved arrows to show the
breaking and forming of bonds. Explain why this product is the major product formed.
3
4. (8 pts) Show the major product expected under the following reaction conditions, name that product, and then give a detailed mechanism (using curved arrows) that describes its formation.
5. (8 pts) Provide the major product expected under the following conditions and then a detailed mechanism for its formation that includes all steps that lead to this product.
6. (6 pts) Rank the following in decreasing order of reaction rate in SN1 with HBr (4 = fastest, 1 = slowest) and then give a brief explanation for your choices.
4
7. (10 pts) On the axes given below, draw a complete reaction profile for the following reaction that includes diagrams of all intermediates and transition states involved.
P.E.
reaction coordinate
HBr
Br
8. (8 pts) The following hydroboration-oxidation sequence results in the alkylborane and alcohol shown below. Explain how the regiochemical and stereochemical outcomes help determine the mechanism in each step.
5
9. (15 pts) Give the ultimate major product expected in each of the following situations.
1. O3
2. Zn, H2O
Br2, heat
CH3CO3H
Br2 in H2O
H2, Pd
a.
b.
c.
d.
e.CH3
CH3
6
10. (8 pts) Give a mechanism for the following reaction using curved arrows to describe all bond-forming and breaking events. Then draw a transition state for the R.D.S. and explain why this is the major product.
11. (6 pts) Provide the reagents required to complete the following transformations.
12. (5 pts) Dehydration of a tertiary alcohol in the presence of catalytic acid through the E1 pathway is thermo-
dynamically unfavourable since sigma bonds are swapped for a pi bond. Explain how this process is made viable such that the alkene is able to be formed and isolated in high yield.
1
Chemistry 3719, Fall 2012 Exam 2 - Key Name: Student number: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck.
1. (9 pts) Within each of the following pairs of molecules, indicate which will react at a faster rate in the given reaction; then give a brief explanation for your choice in each case.
a.
b.
c.
CH3
H3C H
CH3or in electrophilic addition
BrH H
BrD D
or in E2 elimination
OH OHor in SN2 substitution
would produce 3o carbocation
as opposed to secondary
C-H bonds are weaker andtherefore easier to break
Primary carbon is much moreaccessible than tertiary
2
2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or common names for substituents.
a.
b.
c.
Br
OH
(Z)-5-bromo-7-methyloct-4-en-2-ol
OH
F F
4,4-difluoro-3-propylcyclohex-2-enol
I
Cl
(Z)-4-chloro-5-iodo-2-methyloct-4-ene
3. (8 pts) Provide a detailed mechanism for the following transformation that uses curved arrows to show the
breaking and forming of bonds. Explain why this product is the major product formed.
H2SO4,OHH2O H
OH2H
H2O
H2O
The secondary carbocation that is formed undergoes rearrangement to produce a better tertiary cation that no longer has the strained cyclobutyl ring involved. The tertiary carbocation is then deprotonated to give the most highly substituted alkene which is stabilized by four electron-donating alkyl groups through inductive effects.
3
4. (8 pts) Show the major product expected under the following reaction conditions, name that product, and then give a detailed mechanism (using curved arrows) that describes its formation.
HBrH
Br
1-bromo-2-cyclopentylcycloheptane
HO OH
OHBr H
Br
Br
Br H
5. (8 pts) Provide the major product expected under the following conditions and then a detailed mechanism for its formation that includes all steps that lead to this product.
C
CH3
CH3
CH3CH2 HBr2, heat
Br Br
Br
C
CH3
CH3
CH3CH2 Br
C
CH3
CH3
CH3CH2 Br Br C
CH3
CH3
CH3CH2 Br
6. (6 pts) Rank the following in decreasing order of reaction rate in SN1 with HBr (4 = fastest, 1 = slowest)
and then give a brief explanation for your choices.
OH
OHOH
CH3OH
432 1
The better the possible carbocation, the faster the SN1 reaction; 3° > 2° > 1° > CH3
4
7. (10 pts) On the axes given below, draw a complete reaction profile for the following reaction that includes diagrams of all intermediates and transition states involved.
P.E.
reaction coordinate
HBr
Br
Br
A B
C
A =
B =
C =
H Br+
-
+
+
+
-
H
Br
‡
‡
‡
8. (8 pts) The following hydroboration-oxidation sequence results in the alkylborane and alcohol shown below. Explain how the regiochemical and stereochemical outcomes help determine the mechanism in each step.
CH2CH3
CH2CH3
H
BH NaOH
H2O2B
CH2CH3
HOH
CH2CH3
B
H Since H and B add tosame side of substratethis is a syn additionwhich must be concerted
CH2CH3
HB
OOH
Since the stereochemistryof the OH group is the sameas the B, this must involve aconcerted migration step
The first step involves regioselective addition of the borane reagent such that the larger substituent on the alkene avoids the large bicyclic framework on boron; the oxidation step results in stereochemical retention, which is only possible with a concerted migration step.
5
9. (15 pts) Give the ultimate major product expected in each of the following situations.
1. O3
2. Zn, H2O
Br2, heat
CH3CO3H
Br2 in H2O
H2, Pd
a.
b.
c.
d.
e.CH3
CH3
H
O
O
H
Br
O
Br
OH
CH3
CH3
H
H
6
10. (8 pts) Give a mechanism for the following reaction using curved arrows to describe all bond-forming and breaking events. Then draw a transition state for the R.D.S. and explain why this is the major product.
NaOCH2CH3
Br
H
Br
H
OCH2CH3
OCH2CH3
‡-
-
E2
The major product is the most highly-substituted and stabilized alkene (tetrasubstituted)
11. (6 pts) Provide the reagents required to complete the following transformations.
12. (5 pts) Dehydration of a tertiary alcohol in the presence of catalytic acid through the E1 pathway is thermo-
dynamically unfavourable since sigma bonds are swapped for a pi bond. Explain how this process is made viable such that the alkene is able to be formed and isolated in high yield.
Run the reaction at high temperature to increase the contribution of entropy to the overall free energy of the system (G = H – TS) since the reaction is entropically favoured (1 mole of alcohol produces two moles of product; alkene and water). High temperature also allows the more volatile alkene to be removed by distillation which will then force the equilibrium towards product to compensate.
1
Chemistry 3719, Fall 2012 Exam 3 Name: Student number: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck.
1. (9 pts) For each of the following pairs of molecules, provide the configuration of each chiral centre and then indicate whether the two molecules within a pair are enantiomers, diastereomers, or are identical.
a.
b.
c.
and
and
and
OH
Br
CH3
CH3
H Br
H OH
O CH3
CH3 O CH3
CH3
CH3
H OHCH2Cl
FH H3CCH2Cl
OH
F
2
2. (9 pts) Give each of the following organic molecules an acceptable name using any systematic or common names for substituents where appropriate. Be sure to include stereochemical designators where needed.
a.
b.
c.
F
OH
Br
Cl
F
HO CH3 3. (8 pts) For the following conversion, provide a detailed mechanism for the first operation only (i.e. reaction
of the alkene with O3) that uses curved arrows to show the breaking and forming of bonds.
3
4. (15 pts) Give the expected products, major and minor where applicable, in each of the following situations. Be sure to take into account any changes in stereochemistry that may occur.
1.
2. NaCN, DMF
1. NaNH2, DMF
CH3OH
NaOCH3, DMF
1. NaN3, DMSO
a.
b.
c.
d.
e.
OH SO2ClH3C
pyridine
O
CC
H
2. CH3CH2CH2Br
O
H
BrH
CH2OH
CH3
H OH
H I
2. H2, Pd
I
4
5. (8 pts) Provide the major product expected under the following reaction conditions, and then give a detailed mechanism (using curved arrows) that describes its formation.
6. (8 pts) The following solvolysis conditions give two major products in equal amounts but, when measured for the mixture, []D ≠ 0. Provide the products and a mechanism for this process, as well as an explanation for the optical rotation data.
7. (6 pts) Rank the following in decreasing order of reaction as nucleophiles in SN2 reactions (4 = fastest, 1 = slowest) and then give a brief explanation for your choices.
5
8. (8 pts) The following conditions induce a free radical halogenation process at the allylic position with only two products forming with a combined []D = 0; give a mechanistic explanation for this observation.
9. (8 pts) The following reactions have only slight differences; however the ratio of products formed in each
case is dramatically different. Provide a detailed mechanistic explanation for this data.
6
10. (8 pts) Give the major products expected from each step in the following synthetic sequence. Be careful to take into account any stereochemical issues along the way.
11. (6 pts) Convert the following stereochemical representations as directed. Working out R/S configurations
might help but are not required as part of the answer.
a.
b.
OH
OH
Br
O to Fischer
to Wedge-DashH O
CH3
H F
Cl H
12. (7 pts) Typical SN1 and SN2 reactions are promoted by different types of solvents, namely polar protic and
polar aprotic, respectively. Describe two solvents used for SN1, two for SN2, and then explain your choices.
1
Chemistry 3719, Fall 2012 Exam 3 Key Name: Student number: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck.
1. (9 pts) For each of the following pairs of molecules, provide the configuration of each chiral centre and then indicate whether the two molecules within a pair are enantiomers, diastereomers, or are identical.
a.
b.
c.
and
and
and
(R)(R)
OH
Br
CH3(S)
(R)
CH3
H Br
H OH
(S)(S)
O CH3
CH3
(S)
(S)
O CH3
CH3
CH3
H OHCH2Cl
FH H3C (R)(S) CH2Cl
OH
F
diastereomers
equivalent
enantiomers(S)
(R)
2
2. (9 pts) Give each of the following organic molecules an acceptable name using any systematic or common names for substituents where appropriate. Be sure to include stereochemical designators where needed.
a.
b.
c.
F
OH
(3R,6S)-6-fluoro-7-methyloct-4-yn-3-ol
Br
Cl (R,Z)-2-bromo-5-chloro-6-methylhept-2-ene
F
HO CH3
(1S,3R)-3-fluoro-5-methylcyclohept-4-enol
3. (8 pts) For the following conversion, provide a detailed mechanism for the first operation only (i.e. reaction
of the alkene with O3) that uses curved arrows to show the breaking and forming of bonds.
H
H
1. O3
H
H2. Zn, H2O
O
H
H
O
H
H
O OO
H
H
OOO
H
H
H
HO
O
O
O
OO
3
4. (15 pts) Give the expected products, major and minor where applicable, in each of the following situations. Be sure to take into account any changes in stereochemistry that may occur.
1.
2. NaCN, DMF
1. NaNH2, DMF
CH3OH
NaOCH3, DMF
1. NaN3, DMSO
a.
b.
c.
d.
e.
OH OTs CNSO2ClH3C
pyridine 1. 2.
O
CC
H
2. CH3CH2CH2BrO
CCNa1. 2.
O
CC
CH2CH2CH3
O
+
H H H
BrH
HOCH3
1. 2.
SN1 - racemic
SN2 - inversion
SN2 - inversion E2
CH2OH
CH3
H OH
H I
2. H2, Pd
CH2OH
CH3
H OH
N3 H
CH2OH
CH3
H OH
H2N H
1. 2.
SN2 - inversion
I
O
OCH3
O
OCH3
4
5. (8 pts) Provide the major product expected under the following reaction conditions, and then give a detailed mechanism (using curved arrows) that describes its formation.
CC
H
dilute H2SO4
(H+/H2O)
C
O
CH3
C H
H
HO
H
H
C H
H
OH H
C H
H
OH
C H
H
OH
H
C H
H
OH
H
H2O
H2O
HO
H
H
H2O
6. (8 pts) The following solvolysis conditions give two major products in equal amounts but, when measured
for the mixture, []D ≠ 0. Provide the products and a mechanism for this process, as well as an explanation for the optical rotation data.
Br
OH
OH
OH
OH
OH
H2O+
OH
OH
OH2
50/50 R/S
- H+- H+
Products are actuallydiastereomers and notenantiomers so theoptical rotations will notcancel each other out.
Flat carbocation, attackedfrom both sides
7. (6 pts) Rank the following in decreasing order of reaction as nucleophiles in SN2 reactions (4 = fastest, 1 =
slowest) and then give a brief explanation for your choices.
ONa
O
OH
O SNa ONa
4 32 1
RSNa has charge on larger S which is easier to share than O (electronegativity);Localized charge on O is more reactive (and more nucleophilic) than delocalizedcharge on carboxylate; neutral carboxylic acid is most stable and least reactive
5
8. (8 pts) The following conditions induce a free radical halogenation process at the allylic position with only two products forming with a combined []D = 0; give a mechanistic explanation for this observation.
Br2
heat
Br Br
Br Br
2 Br H
initiation
propagation
propagationor
termination
The prochiral radical intermediate is delocalized, however the resonance forms areequivalent; the termination or propagation steps lead to the same racemic products
9. (8 pts) The following reactions have only slight differences; however the ratio of products formed in each
case is dramatically different. Provide a detailed mechanistic explanation for this data.
OTs
OTsCH3
OCH3
KOC(CH3)3
NaOCH3
+
CH3
only product
major minor
In the top reaction the electrophile is secondary and the nucleophile is small; this willall SN2 to occur with a minor E2 side-product, the alkene. In the bottom reaction theelectrophile is tertiary and more crowded which stops the SN2 from operating. Thelarge nucleophile/base will allow only E2 to occur, in this case to give the conjugatedalkene product exclusively.
H
6
10. (8 pts) Give the major products expected from each step in the following synthetic sequence. Be careful to take into account any stereochemical issues along the way.
Br 1. NaI, acetone
2. NaOH, DMF
3. NaNH24. CH3CH2I
I1.
OH2.
ONa3.
OCH2CH34.
Finkelstein, SN2 with inversion
SN2 with inversion
Acid-Base reaction
SN2 with inversion
11. (6 pts) Convert the following stereochemical representations as directed. Working out R/S configurations might help but are not required as part of the answer.
12. (7 pts) Typical SN1 and SN2 reactions are promoted by different types of solvents, namely polar protic and
polar aprotic, respectively. Describe two solvents used for SN1, two for SN2, and then explain your choices.
SN1 reactions work best in polar protic solvents, which are capable of H-bonding to leaving groups and then facilitating their departure. These polar solvents will also help stabilize the transition states and the carbocation formed during this process, and will ultimately serve as the nucleophile in such solvolysis reactions. In SN2 reactions the H-bonding ability of polar protic solvents is a disadvantage since that reduces nucleophile reactivity; polar aprotic solvents solubilize the reagents but do not attenuate their reactivities. Polar aprotic solvents will stabilize polar bimolecular transition states while not interfering as nucleophiles themselves.
1
Chemistry 3719, Fall 2006 Exam 1 Name: Student number: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck.
1. (6 pts) Draw a second resonance structure for each of the following anions.
HC
O
N H
C
O
SH
O
a.
b.
c.
2
2. (15 pts) Give the products from each of the following acid-base reactions. Then give the acids on each side of the equations approximate pKa values and indicate which side of each equation is favored.
+ H2O
NaOH+
OH
+
OH+ NaNH2
+
C CLiCH3
OH
NH2CH3CH2CH2Li
CH3COK
O
O
a. b. c. d. e.
3
3. (5 pts) Which of the two molecules below is the stronger acid? Give their approximate pKa values and explain your choice in terms of the relative stabilities of the respective conjugate bases.
O
OH OH
4. (12 pts) Draw Newman projections that correspond to each of the following:
a. The lowest energy conformation of n-nonane looking down the C3 – C4 bond axis.
b. A gauche conformation of 1-bromo-3-fluoropropane looking down the C1 – C2 bond axis.
c. The least stable conformation of 2-methylheptane along the C4 – C5 bond axis.
4
5. (5 pts) Give the hybridization of each of the highlighted atoms in the following molecules (sp3, sp, etc.).
O
CH OH
OCO
O
CH CH3
O
HC C CH3H
6. (10 pts) The following questions relate to the cis and trans- isomers of 1-fluoro-2-isopropylcyclohexane.
a. Draw two “ring-flipped” conformations of the cis-isomer and circle the more stable of the two.
b. Draw two “ring-flipped” conformations of the trans-isomer and circle the more stable of the two.
c. Using Newman projection terminology; what is the relationship between the fluoro and isopropyl groups in the least stable of all of the conformations you have drawn above (one word answer)?
5
7. (20 pts) Provide acceptable names for the following compounds.
Cl
CH(CH3)2
OH
Cl
CH3
CH3
Br Br
F
a. b. c. d. e.
6
8. (6 pts) For the highlighted atom in each of the following molecules fill in the ground state electron configuration (i.e from the Periodic Table) in the given orbitals (the horizontal lines). Then draw a picture, on the right, of the hybridization model that best explains the bonding in the highlighted atoms.
Energy hybridizeH
CO
H
Energy hybr idizeH
OH
9. (6 pts) Circle any of the following that are 2o alcohols or alkyl halides.
Cl Br
CH3CH2CH(OH)CH3
OH
F
CH(CH3)2CH3
OHCH3
7
10. (15 pts) Draw acceptable structures for each of the following molecules.
a. cis-1-cyclopropyl-3-methylcyclohexane b. 3,3,8-trimethyl-1-dodecanol c. trans-1-t-butyl-2-ethylcyclobutane d. 6-ethyl-2,3,5,5-tetramethyldecane e. bicyclo[5.2.0]nonane
1
Chemistry 3719, Fall 2006 Exam 1 Key Name: Student number: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck.
1. (6 pts) Draw a second resonance structure for each of the following anions.
HC
O
N H
C
O
SH
O
a.
b.
c.
HC
O
N H
C
O
SH
O
2
2. (15 pts) Give the products from each of the following acid-base reactions. Then give the acids on each side of the equations approximate pKa values and indicate which side of each equation is favored.
+ H2O
NaOH+
OH
+
OH+ NaNH2
+
C CLiCH3
OH
NH2CH3CH2CH2Li
CH3COK
O
O
+ LiOH
H2O+
OK
+
ONa+ NH3
+
C CHCH3
ONa
NHLi CH3CH2CH3
CH3COH
O
O
pKa ~ 16 pKa ~ 26
RHS
f avored
RHS
favored
pKa ~ 5 pKa ~ 16
pKa ~ 36 pKa ~ 60
RHS
favored
RHS
favored
pKa ~ 16 pKa ~ 36
pKa ~ 10 pKa ~ 5
LHS
favored
a. b. c. d. e.
3
3. (5 pts) Which of the two molecules below is the stronger acid? Give their approximate pKa values and explain your choice in terms of the relative stabilities of the respective conjugate bases.
O
OH OH
O
O O
base base
O
O
pKa ~ 5 pKa ~ 16
The electron-withdrawing C=O in the carboxylic acid makes the OH proton more positive than in the alcohol, and the C=O also
allows the charge in the anion to delocalize thus making the conjugate base more stable. 4. (12 pts) Draw Newman projections that correspond to each of the following:
a. The lowest energy conformation of n-nonane looking down the C3 – C4 bond axis.
H
HH
H
(CH2)4CH3
H H
CH2CH3
HHAnti
b. A gauche conformation of 1-bromo-3-fluoropropane looking down the C1 – C2 bond axis.
Br
FHH
H
H
H
H CH2F
Br
HHGauche
c. The least stable conformation of 2-methylheptane along the C4 – C5 bond axis.
HH
HH H
H
CH2CH3
CH2CH(CH3)2
HH
Eclipsed
4
5. (5 pts) Give the hybridization of each of the highlighted atoms in the following molecules (sp3, sp, etc.).
O
CH OH
OCO
O
CH CH3
O
HC C CH3H
sp2 sp sp3
sp2
sp
6. (10 pts) The following questions relate to the cis and trans- isomers of 1-fluoro-2-isopropylcyclohexane.
a. Draw two “ring-flipped” conformations of the cis-isomer and circle the more stable of the two.
F
CH(CH3)2F
(CH3)2HC
Larger group equatorial
b. Draw two “ring-flipped” conformations of the trans-isomer and circle the more stable of the two.
F
(CH3)2HC
F
CH(CH3)2 Both larger groups equatorial
c. Using Newman projection terminology; what is the relationship between the fluoro and isopropyl groups in the least stable of all of the conformations you have drawn above (one word answer)?
F
H
iPr
H
H
H
H
HAnti
5
7. (20 pts) Provide acceptable names for the following compounds.
Cl
CH(CH3)2
OH
Cl
CH3
CH3
Br Br
F
trans-1-chloro-2-isopropylcyclopentane
5-chloro-6-methylheptan-2-ol
or
5-chloro-6-methyl-2-heptanol
5-ter t-butyl-2-ethyl-1-methylcyclooctane
cis-1,4-dimethylcyclohexane
2,2-dibromo-5-fluoro-4-methylheptane
a. b. c. d. e.
6
8. (6 pts) For the highlighted atom in each of the following molecules fill in the ground state electron configuration (i.e from the Periodic Table) in the given orbitals (the horizontal lines). Then draw a picture, on the right, of the hybridization model that best explains the bonding in the highlighted atoms.
Energy hybr idizeH
CO
H
Energy hybr idizeH
OH
sp2 (to σ bonds)
p (to π bond)
sp3 (to σ bonds)
C: 1s2 2s2 2px1 2py
1
O: 1s2 2s2 2px2 2py
1 2py1
9. (6 pts) Circle any of the following that are 2o alcohols or alkyl halides.
Cl Br
CH3CH2CH(OH)CH3
OH
F
CH(CH3)2
CH3
OHCH3
7
10. (15 pts) Draw acceptable structures for each of the following molecules.
a. cis-1-cyclopropyl-3-methylcyclohexane
CH3
b. 3,3,8-trimethyl-1-dodecanol
HO
c. trans-1-t-butyl-2-ethylcyclobutane
CH3CH2 C(CH3)3
d. 6-ethyl-2,3,5,5-tetramethyldecane
e. bicyclo[5.2.0]nonane
1
Chemistry 3719, Fall 2006 Exam 2 Name: Student Number: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck.
1. (9 pts) Give the expected major and minor products from the following reaction then give a complete
mechanism for how the major product is formed.
OHH2SO4
2
2. (9 pts) Give structures for each of the following molecules.
a. 1,3-dichloro-6-isopropylcyclohept-1-ene
b. 2-bromo-5-methyl-4-vinylcyclohexanol
c. 3-bromo-5-fluorohex-5-en-2-ol
3. (10 pts) Give the major monobrominated product from the following reaction and then show a mechanism
that includes all the possible ways how that product is formed during the reaction.
Br2, heat
3
4. (18 pts) Give organic product(s), labeling major and minor where applicable, for the following reactions.
Br2, heat
H2, Pt
NaOCH2CH3
H3PO4
HBr
HBr
OH
CH3
CH3
Br
OH
CH3
CH3
a. b. c. d. e. f.
4
5. (9 pts) Give a complete mechanism (using curved arrows) for the following reaction.
CH3
OH
Br
CH3HBr
6. (8 pts) Provide the expected products in the following reaction and then a detailed mechanism for the
formation of the major product only. Explain why the product you chose is major.
HCl
5
7. (12 pts) Give acceptable names for each of the following molecules.
OH
Br
Cl
HO
FBr
8. (10 pts) Draw the reaction profile (potential energy vs. reaction coordinate) for the following conversion
that includes picture(s) of the transition state(s) involved.
Br NaOCH3
a. b. c. d.
Potential energy
Reaction coordinate
6
9. (6 pts) Circle the more stable species in each of the following pairs and give a brief explanation of your choices.
vs.
vs.
vs.
10. (9 pts) For each of the following reactions, give the major product expected and then name that product.
Cl
NaOCH3
OH HCl
H2SO4, H2O
a. b. c.
a. b. c.
1
Chemistry 3719, Fall 2006 Exam 2 Name: Student Number: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck.
1. (9 pts) Give the expected major and minor products from the following reaction then give a complete
mechanism for how the major product is formed.
OHH2SO4
+
major minorH O
H
H
OH2
H OH2
2
2. (9 pts) Give structures for each of the following molecules.
a. 1,3-dichloro-6-isopropylcyclohept-1-ene
Cl
Cl
b. 2-bromo-5-methyl-4-vinylcyclohexanol
OH
Br
c. 3-bromo-5-fluorohex-5-en-2-ol
HO
FBr 3. (10 pts) Give the major monobrominated product from the following reaction and then show a mechanism
that includes all the possible ways how that product is formed during the reaction.
Br2, heatBr
Br Br Br2 x
H
BrBr Br
Br
Br Br
3
4. (18 pts) Give organic product(s), labeling major and minor where applicable, for the following reactions.
Br2, heat
H2, Pt
NaOCH2CH3
H3PO4
HBr
HBr
OH
CH3
CH3
Br
OH
CH3
CH3
Br+
Br
major minor
BrBr
major minor
CH3
CH3
CH3
CH3
major minor
CH3
CH3
H
H
only one product(from syn addition)
+
+
+
major minor
Bronly one product
(via 3o carbocation)
a. b. c. d. e. f.
4
5. (9 pts) Give a complete mechanism (using curved arrows) for the following reaction.
CH3
OH
Br
CH3HBr
H Br
CH3
OH2
CH3
CH3
Br
6. (8 pts) Provide the expected products in the following reaction and then a detailed mechanism for the
formation of the major product only. Explain why the product you chose is major.
HCl
ClH Cl
H+
major minorH Cl
H Cl
Major product formed via more stabilized carbocation (Markovnikoff)
5
7. (12 pts) Give acceptable names for each of the following molecules.
OH
Br
Cl
HO
FBr
2-isopropenylcyclopentanol
(E)-6-bromo-4-methylhept-3-eneor
trans-6-bromo-4-methylhept-3-ene
4-chlorocyclohex-2-enol
3-bromo-5-f luoro-2-methylhex-2-ene
8. (10 pts) Draw the reaction profile (potential energy vs. reaction coordinate) for the following conversion
that includes picture(s) of the transition state(s) involved. Br NaOCH3
Br
HOCH3
δ
δ
E2
Br
a. b. c. d.
Reaction coordinate
Potential energy
6
9. (6 pts) Circle the more stable species in each of the following pairs and give a brief explanation of your choices.
vs.electron-donating alkyl groups help stabilize
sp2 C in alkenes - the more alkyl groups the morestable the alkene (tetra- vs. trisubstituted)
vs.
Electron-deficient radicals are stabilized by thesharing of electron density from adjacent σ bonds
(tertiary vs. secondary radical)
Trans alkene is more stable than the cis isomerhere since the alkyl groups attached to the
double bond will not interactvs.
10. (9 pts) For each of the following reactions, give the major product expected and then name that product.
Cl
NaOCH32-methylhex-2-ene
OH HCl Cl1-chloro-3,3-dimethylpentane
H2SO4, H2OOH
3-methylheptan-3-ol
a. b. c.
a. b. c.
1
Chemistry 3719, Fall 2006 Exam 3 Name: Student Number: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck.
1. (6 pts) Give the organic product(s) from the following reaction and then discuss the stereochemical
outcome in terms of the mechanism that is operating.
Br2
(cold, dark)
2
2. (12 pts) Provide acceptable names for the following molecules that include the appropriate stereochemical descriptors (R/S, cis/trans).
Cl
F
OH
CH2OH
CH3
F H
Br Cl
3. (12 pts) Draw structures for each of the following molecules.
a. b. c.
a. (1R,3R)-3-vinylcyclopentanol b. (1S,2S)-1,2-dibromocyclohexane c. (3R,4S)-4-chlorohex-1-ene-3-ol
3
4. (10 pts) Draw all of the possible stereoisomers of 4-bromo-2-hexanol as “wedge-dash” depictions, then label each stereogenic centre as being either the R or S configuration. Finally, relate the isomers to each other as either enantiomers or diastereomers.
5. (6 pts) Rank the following molecules in terms of how fast they will react with NaN3 in DMF solution; 1 is
the fastest reaction, 4 is the slowest reaction. Briefly explain your choices.
H3C CH3 H H
BrBr
H3C H
BrH
H H
Br
4
6. (18 pts) Give the expected products from the following reactions, labeling major and minor where needed. When more than one set of reagents are given the product(s) from each step is(are) required.
CC
H 1. NaNH2
2. CH3CH2Br
peroxides, ∆
1. Br2, H2O
NaN3, DMF
1. O3
2. Zn, H2O
HBr
Br
2. NaOH
O
OOH
a. b. c. d. e. f.
5
7. (8 pts) Draw a mechanism for the following portion of the olefin hydroboration/oxidation reaction.
B H
2
B O
2
B
2
HNaOH, H2O2
H
8. (6 pts) For the following portion of the ozonolysis reaction, use curved arrows to show a mechanism for how the compound on the left converts to the product on the right.
O3
OO
O
6
9. (9 pts) Within each of the following pairs of molecules, identify any stereogenic centres, label them as having the R or S configuration, and then indicate the relationship between the two molecules; are they enantiomers, diastereomers, or are they identical?
a.
Br
Cl
CH3
Cl H
H Br
CH2CH3
and
b. OH
Cl
and
Cl
OH
c.
CH3
HO H
F H
CH3
and
CH3
H OH
H F
CH3
10. (7 pts) The following bromide has an optical rotation ([α]D) of +38°. After reaction with water the measured
[α]D of the product mixture is found to be 0°. Give the products and explain the change in optical rotation in terms of the mechanism and the structure of the intermediate formed during this reaction.
Br H2O
7
11. (6 pts) Answer each of the following questions by circling your choice and then giving a few words of explanation for why you made that choice. a. Which of the following species is the better nucleophile? Why?
O O
O
b. Which of the following would react faster with NaCN in DMF? Why?
Br Cl
c. Which of the following solvents would allow for faster SN2 reactions? Why?
H NCH3 OH
O
CH3
1
Chemistry 3719, Fall 2006 Exam 3 Key Name: Student Number: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck.
1. (6 pts) Give the organic product(s) from the following reaction and then discuss the stereochemical
outcome in terms of the mechanism that is operating.
Br2
(cold, dark)
Br
Br only trans product formed
BrBr
δ+ δ-
Br
Br
Isolation of the trans product only suggests that the Br adds and forms a modified carbocation in which Br stabilizes by bonding to both carbons of the double bond; the bromide anion can then only approach from the opposite face (here from below) to give the trans product.
2
2. (12 pts) Provide acceptable names for the following molecules that include the appropriate stereochemical descriptors (R/S, cis/trans).
Cl
(R)-4-chloro-5,5-dimethylhept-1-ene
F
OH (1R,3R)-3-fluorocyclooctanol
CH2OH
CH3
F H
Br Cl
(2R, 3S)-2-bromo-2-chloro-3-fluorobutan-1-ol
3. (12 pts) Draw structures for each of the following molecules.
HO
Br
Br
Cl
OH
a. b. c.
a. (1R,3R)-3-vinylcyclopentanol b. (1S,2S)-1,2-dibromocyclohexane c. (3R,4S)-4-chlorohex-1-ene-3-ol
3
4. (10 pts) Draw all of the possible stereoisomers of 4-bromo-2-hexanol as “wedge-dash” depictions, then label each stereogenic centre as being with the R or S configuration. Finally, relate the isomers to each other as either enantiomers or diastereomers.
(S) (R)
OHBr
(R) (S)
OHBr
(S) ( S)
OHBr
(R) (R)
OHBr
diast.
diast.
d iast.enant. enant.
diast.
2 stereogenic centres, therefore 4 (2n) possible stereoisomers.
No internal symmetry, therefore no meso possibility 5. (6 pts) Rank the following molecules in terms of how fast they will react with NaN3 in DMF solution; 1 is
the fastest reaction, 4 is the slowest reaction. Briefly explain your choices.
H3C CH3 H H
BrBr
H3C H
BrH
H H
Br
4 2 1 3
The rate of the SN2 reaction is slowed by local crowding, which makes it more difficult for the nucleophile (N3-) to approach the electrophilic carbon. The fastest reaction here will occur with substrate 1, which is a simple 1° system with little extra bulk at the β- and γ-carbon atoms. Substrate 2 has a bulk cyclohexyl group at the γ-carbon, and this bulk increases with the addition of further methyl groups in 3 and 4.
4
6. (18 pts) Give the expected products from the following reactions, labeling major and minor where needed. When more than one set of reagents are given the product(s) from each step is(are) required.
CC
H 1. NaNH2
2. CH3CH2Br
peroxides, ∆
1. Br2, H2O
NaN3, DMF
1. O3
2. Zn, H2O
HBr
Br
2. NaOH
O
OOH
CCNa1. 2. C
C
+
Br Br HH
major
1. 2.
Br
OH
O
N3
1. 2.OO
OO
O
O
a. b. c. d. e. f.
5
7. (8 pts) Draw a mechanism for the following portion of the olefin hydroboration/oxidation reaction.
B H
2
B O
2
B
2
HNaOH, H2O2
H
BH
2
B
2
Hconcerted
addi tion1.
2. H O O HHO O O H
B
2
OOH
B O
2
Hmigration
8. (6 pts) For the following portion of the ozonolysis reaction, use curved arrows to show a mechanism for how the compound on the left converts to the product on the right.
O3
OO
O
OO
O
OO
O
OO
OH
H
OO
O H
H
6
9. (9 pts) Within each of the following pairs of molecules, identify any stereogenic centres, label them as having the R or S configuration, and then indicate the relationship between the two molecules; are they enantiomers, diastereomers, or are they identical?
a.
(R)(S)
Br
Cl
CH3(S)
(S)Cl H
H Br
CH2CH3
and diastereomers
b.
(S)(S)
OH
Cl
and (S)(S)
Cl
OH
identical
c.
CH3(R)
(S)HO H
F H
CH3
and
CH3(S)
( R)H OH
H F
CH3
enantiomers
10. (7 pts) The following bromide has an optical rotation ([α]D) of +38°. After reaction with water the measured
[α]D of the product mixture is found to be 0°. Give the products and explain the change in optical rotation in terms of the mechanism and the structure of the intermediate formed during this reaction.
Br H2O OH HO
+
enantiomers
H2O
H2O OH2 H2O
+
-H -H
The 3° alkyl bromide will produce a planar carbocation during this solvolysis reaction, which is then attacked from either side by the nucleophile, in this case water. The approximately equal chance of attacking either side of the cation leads to approximately equal amounts of enantiomeric products, which explains the observed optical rotation change.
7
11. (6 pts) Answer each of the following questions by circling your choice and then giving a few words of explanation for why you made that choice. a. Which of the following species is the better nucleophile? Why?
O
O
O
The circled nucleophile is less stable since the charge is localized, it will therefore be more reactive in substitution reactions than the species on the right in which the charge is delocalized.
b. Which of the following would react faster with NaCN in DMF? Why?
ClBr
Br is a better leaving group than Cl since Br anion is more stable than Cl anion (size); SN2 Reactions such as these go faster with better leaving groups.
c. Which of the following solvents would allow for faster SN2 reactions? Why?
OHH NCH3
O
CH3
Polar aprotic solvents work better in SN2; polar protic, such as the alcohol here, will H-bond
to the nucleophile thereby forming a solvent “coating” around the nucleophile; this will slow down its approach to the electrophilic carbon.
