1. CHE 230 Organic Chemistry I. Exam 4. Name: KEY. Student number: Before
you begin this exam: First: You are allowed to have a simple model set and a.
CHE 230 Organic Chemistry I Exam 4 Name: KEY Student number: Before you begin this exam: First: You are allowed to have a simple model set and a calculator at your seat. Please put away all other materials. Second: Place your student identification on your desk. A proctor will come around to check everyone’s ID. Third: Read through the entire exam. Your goal, as always, is to score as many points as possible. Do not waste time on problems that you can’t do if there are others that look easy. Fourth: READ EACH QUESTION CAREFULLY. Be sure you answer the question that is asked.
1. 2. 3. 4. 5. 6. 7. 8.
10 points
10 points
14 points
10 points
20 points
25 points
20 points
25 points
9. 10.
10 points
35 points
11. 15 points 12. 10 points 13. 15 points 14. 10 points 15. 10 points 16. 25 points 17. 6 points 18. 15 points 19. 15 points Total:
1
1.
(10 points) Draw the Lewis dot structures of the following molecules and ions. Please show electrons and electron pairs as dots, not as lines.
a)
N
N
N
N
N
N
b) O
O
C H
H
C
N
H
H N
H
H
2.
(10 points) Determine the formal charge on the indicated atoms in the following molecules.
+1 The charge is _______ O
CH3
-1 The charge is _______
N
O
2
3.
(14 points) Assign the hybridization for each of the indicated atoms. O
B
N
N
C
NH2
CH3
N
B
B N
sp2
sp3 sp
sp
sp2
sp2
3
sp2
4.
Dimethyl sulfoxide (DMSO, shown below) is a common solvent.
a) (5 points) Draw a second resonance form for DMSO.
O
O
S
S
CH3
CH3
CH3
CH3
DMSO
b) (5 points) The geometry of sulfur in DMSO is tetrahedral. Based on this, circle the resonance form that must be the major contributor to the hybrid.
5.
(20 points) Classify each compound below as either aromatic or antiaromatic.
H
H N
aromatic
aromatic
H
antiaromatic
antiaromatic
H
aromatic
3
6.
Lipitor, a drug used for lowering blood cholesterol ($12.8 billion in sales in 2008!), is shown below. O
OH
NH
OH
O
N
OH
Atorvastatin (Lipitor)
F
Let’s look at a likely precursor to the heptanoic acid side chain. Call it “Compound A.” OH
OH H
O H OH
H2N
Compound A a)
(10 points) Assign the R,S designations to the two stereogenic centers in compound A.
Both have the R configuration b)
(15 points) Below are several stereoisomers of compound A. For each one, determine if the compound shown is an enantiomer or a diastereomer of compound A. OH
OH H
O H OH
H2N
This is a(n)
diastereomer
of compound A.
diastereomer
of compound A.
OH
OH H
H2N
O H OH
This is a(n)
4
OH
OH H
O H OH
H2N
This is a(n)
enantiomer
of compound A.
7.
(20 points) Give the IUPAC name for each of the following compounds. Be sure to include the E, Z designations where appropriate.
a)
2,3,3-trimethylcyclohexene
b)
2-methyl-2-heptene
c) OH
4-methyl-1-pentanol
d)
3-E-2-methyl-1,3-hexadiene
5
8.
(25 points) Three conformations s-‐butylcyclohexane are drawn below. These differ by 120 degree rotational steps around the central bond. On the chart below, sketch the rotational energy diagram for rotation between these different conformations. Be sure your diagram shows i) which conformation is lowest in energy; and ii) which point (between which conformations) is highest in energy. CH3
H
CH3
H
CH3
C
C
C
H
H
H
CH3
H
C
C H
C CH3
H
B
A
H
CH3
C
H
CH3 CH3
H
Cy
H H
Cy CH3
H
CH3
H
CH3
Cy H
H
CH3 H
A
B
C
6
9.
(10 points) Draw the most stable chair conformation for 1,2,3,4-‐tetramethylcyclo-‐ hexane (below). Be careful to get the relative stereochemistry right.
CH3 CH3
CH3
CH3
CH3
10.
The IR spectrum for an organic compound (C8H10O) is given below: 2964 cm-1
3349 cm-1
a) (10 points) What functional groups are likely to be responsible for the labeled bands in the IR spectrum? 3349 cm-‐1: hydroxyl
2964 cm-‐1: C-H (sp3)
Here is the 1H NMR spectrum of the same compound. Integrals are given.
5
2
2 1
7
An expansion of the upfield region of the NMR spectrum is shown here.
And here is the 1H NMR data presented in table form: δ 7.2-‐7.5, multiplet, 5H δ 3.82, triplet, 2H δ 2.87, triplet, 2H δ 2.45, broad singlet, 1H b) (20 points) Using the IR and NMR spectra, determine the structure of this compound. The structure is: OH
c)
(5 points) Based on your structure, what proton is responsible for the broad singlet at 2.45 ppm? The hydroxyl proton
11.
(15 points) Determine how many 13C lines will appear in the 13C NMR spectra of each of the compounds shown here. 1 2 3
2 3
5
2 3
4
4
1
1
4 lines
5 lines
3 lines
8
12.
(10 points) The energy profile diagram below shows two possible pathways for the elimination of HBr in the following reaction. Br
EtO Na
Which of these pathways (1 or 2) is likely to be the concerted E2 elimination pathway?
2
1
Pathway 1 is a concerted path. Pathway 2 is stepwise. 13. (15 points) In the following pairs, which is the stronger acid?
a) NH4+ or CH4?
b) EtOH or PhOH? (Ph = phenyl)
c) EtOH or Et2NH?
9
14.
(10 points) High on the list of the most reactive Diels-‐Alder dienes is ortho-‐xylylene (shown below). In the reaction shown, ortho-‐xylylene adds to a vinyl ether to produce a Diels-‐Alder adduct. O
ortho-xylylene
a) Draw the structure of the product of this Diels-‐Alder reaction. O
b) In no more than one sentence and without exceeding the space provided, explain why ortho-xylylene is so reactive in Diels-‐Alder reactions.
Unlike most Diels-Alder dienes, o-xylylene produces a highly favorable aromatic ring.
15.
(10 points) The less-‐substituted alkene results from the E2 elimination of HBr from the cyclohexane derivative below. Draw the starting material in the conformation required for E2 elimination and point out (one sentence or less) why only the specific isomeric alkene is formed. Br
NaOEt NOT
Br
CH3 H
This is the only anti-periplanar proton for this elimination reaction
10
16.
(25 points) Draw the expected organic product from the following reactions.
a) NaCN
CN
Br
b) Br
tBuO K
c) CH3I O
OCH3
d)
CH3
CH3
CH3
heat, H2O
CH3
CH3
CH3
Cl
OH
e) H N Cl
N
11
17.
(6 points) The reaction of a 2˚ alcohol with a strong acid can result in substitution or elimination (dehydration), depending on the nature of the acid used. Which of these acids would favor elimination (dehydration)? (circle your choice)
HI
HBr
HCl
HF
H2SO4
18.
(15 points) There are many ways to convert alcohols into alkyl halides. For each of the examples below, state whether the reaction proceeds with retention of stereochemistry, inversion of stereochemistry, or loss (racemization) of stereochemistry. SOCl2 Pyridine
OH
retention
loss
inversion
HBr
OH
TsCl
KI
Pyridine
OH
12
19.
(15 points) Draw a detailed reaction mechanism for the reaction shown below. H2SO4 -H2O
OH H
O SO3H
H O
H H
H H
O
H H alkyl shift
END OF EXAM
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