Hourly Third Examination Chemistry S-20
July 16, 2007 8:10 9:20 a.m.
Last Name: First Name: Section TF: Section Time:
Important Notes:
1. This exam consists of 8 problems on 8 pages, plus this cover sheet, and one page for scratch work at the end of the exam. 2. All answers must be written in the spaces provided. Do not write anything in red ink. Answers written on the back of a page will not be graded. Anything written on the scratch page will not be graded. 3. You are allowed to use a set of molecular models for this exam.
Tue AM
Tue PM
(circle one)
Problem 1. 2. 3. 4. 5. 6. 7. 8.
Score ____________ / 12 ____________ / 12 Total Score: ____________ / 12 ____________ / 14 ________________ / 100 ____________ / 14 ____________ / 12 ____________ / 10 ____________ / 14
Chemistry S-20
1
Name:
1. Each of the following transformations can be carried out in one or two steps. Fill in the reagents required for each step. If a second step is not needed, please put an "X" through the second box. Be sure to consider the stereochemistry (if relevant)!
O
a)
1.
2.
O Br
b)
1.
H
2.
1. c)
2.
O
d)
1.
OH
2.
_______ / 12
Chemistry S-20
2
Name:
2. Fill in each box with the organic product(s) of the indicated transformation. (Any chiral starting materials are provided as single, pure enantiomers.) Be sure to give the stereochemistry of each product if it is relevant!
a)
Hg(OAc)2 , H2O
b)
H3C
OH
HCl
CH3
KOtBu
Cl
c)
I
d)
I
1. Zn 2. H2C
CH2
(those are iodine substituents)
_______ / 12
Chemistry S-20
3
Name:
3. Fill in each box with a reactant that would provide the product indicated by the transformation. Be sure to indicate stereochemistry if it is relevant! (If there is more than one possible answer, provide only one.) For full credit, you must reasonably use all reagents listed.
HO
a)
OsO4
CH3 H
H H3C OH
(plus enantiomer, as a racemic mixture)
b)
1. BH3 2. H2O2, OH
HO H
CH2CH3 H
H3C
CH3
(plus enantiomer, as a racemic mixture)
1. BHR2 c) 2. H2O2, OH 3. NaBH4 reduction
OH
d)
NaCN
H
CN
(as a pure, single enantiomer)
_______ / 12
Chemistry S-20
4
Name:
4. Provide a complete synthesis of the following desired products. You may use any inorganic reagents plus the indicated starting materials as a source carbon. of You do not need to show any mechanisms, but please pay attention to stereochemistry if it is relevant. The best answers each require 5 or fewer steps. a) Starting Material: any alcohols you choose.
H
OMe
Desired Product (as a single enantiomer) b) Starting Material: any compounds containing 3 or fewer carbons
O H Me H Me
Desired Product (as a racemic mixture)
_______ / 14
Chemistry S-20
5
Name:
5. The following reaction yields a single predominant organic product: (Ph = phenyl = C6H5) a) Draw the structure of the product in the box below. Be sure to consider stereochemistry!
Ph Me H
OTs H Me
KOtBu
t
BuOH
b) Provide a complete curved-arrow mechanism.
c) Show why this reaction is stereoselective by using a clear diagram or two. You should show clearly any relevant frontier molecular orbital interactions.
_______ / 14
Chemistry S-20
6
Name:
6. Consider the following stereoselective two-step transformation:
Br2, H2O
Me
NaOH
O Me
(as a pure enantiomer) Intermediate X
(as a pure enantiomer)
a) Draw the structure of Intermediate X in the box above. Please indicate stereochemistry. (Hint: Be sure to consider the stereochemistry of the final product.) b) Provide a complete curved-arrow mechanism for all steps of this reaction.
c) In the space below, draw a clear representation of Intermediate X in its most stable "chair" conformation. Please be sure also to draw the isopropyl substituent in its most stable conformation.
_______ / 12
Chemistry S-20
7
Name:
7. Provide a complete curved-arrow mechanism for the following reaction. (You do not need to worry about stereochemistry.)
HO OH
H2SO4
O
_______ / 10
Chemistry S-20
8
Name:
8. The following reaction produces several products, of which two are shown here:
O Br R O
O R O
O Br
Br
Br2
R
+
O
Br
(as a pure enantiomer)
A (as a pure enantiomer)
B (as a pure enantiomer)
a) Draw a complete curved-arrow mechanism that shows how both of these products (A and B) can be formed from this single starting material. Each step of your mechanism should indicate stereochemistry.
b) Which of these two products is more stable? (circle one) A Explain briefly. or B
_______ / 14
This page is for scratch work only. Anything written on this page will not be graded.