Name _______________________________
Exam 1 SOLUTION
Please work in the space provided. Box your answers to set them off. The last page may be torn off
and used for scratch paper. Bring all materials up when you are finished with the exam. Good luck!
1. Analyze the structure of Tilisolol (SelecalTM), a beta blocker used for a variety of cardiac indications.
[6]
a) What is the formula for the molecule?
b) What functional groups are present in the molecule? Circle the functional group on the structure
and name it next to your circle.
Ether
O
Aromatic
Ring
OH
N
N
H
Amine
Alcohol
C17H24N2O3
Alkane
O
Amide
2. Consider the four structures drawn below: [8]
H2C
H2C
N
H2C
N
O
O
N
H3C
H3C
A
H2C
O
H3C
B
N
O
H3C
C
D
a) Which structure is not an allowable resonance contributor/structure for the compound? Explain
your choice.
Structure C is not allowable. The structure violates the octet rule for the nitrogen! Nitrogen cannot go
beyond an octet.
b) Out of the remaining structures, which is the best resonance contributor/structure for the
compound? Explain your choice.
Structure B is best. This structure puts the negative charge on the most electronegative element, every
atom has an octet, and bonding is maximized without violating the octet rule.
3. The connectivity of carbon oxysulfide is O-C-S. [8]
a) Draw the complete Lewis structure for the molecule.
b) What is the hybridization and molecular geometry about the central carbon?
c) Is the molecule polar? If so, which way does the dipole point?
O C S
The carbon is sp-hybridized and has a linear geometry. Since oxygen is more electronegative than
sulfur, there is a dipole in the molecule, pointing towards the oxygen side of the molecule.
Exam 1
Fall 2008
Page 1 of 6
Chemistry& 241
Clark College
4. Nomenclature. [12]
a) Draw the following molecules from the IUPAC names provided.
trans-2-bromo-4-t-butylcyclopentanone
3-bromo-4-methyl-4-hexenal
O
Br
Br
H
O
b) Provide IUPAC names for the following molecules.
OH
OH
F
Cl
F
F
7-chloro-5-isopropyl-2,4-heptanediol
CH3 F
1,1,2,5-tetrafluoro-3,4-dimethylhexene
5. The following IR spectrum is for C6H12. Based on the IR spectrum, is the molecule cyclohexane,
2,3-dimethyl-2-butene (an internal alkene) or 2,3-dimethyl-1-butene (a terminal alkene)? How do
you know this? Support your answer with at least two specific peaks and their significance. [8]
sp2 C-H
C=C
No C=C bond
C=C bond
no sp2 C-H
C=C bond
sp2 C-H
The IR shows both a C=C double stretch at ~1650 cm-1 and an sp2-hybridized C-H stretch at 3100 cm-1
indicates an external alkene, such as 2,3-dibromobutene.
Exam 1
Fall 2008
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Chemistry& 241
Clark College
6. Draw both chair conformers for the following substituted cyclohexane ring. Circle the conformer
that is more stable. [8]
F
H
H
H
F
F
CH3
H
H
H3C
CH3
H
Even though there is only one equatorial group, the t-butyl group is so sterically large that it forces the
ring into a position where it is equatorial.
7. The following three spectra correspond to three of the four molecules below. All molecules have
the formula C6H10O2. Match the IR spectrum to the appropriate compound, and give a brief but
specific reason for your choices. [12]
O
O
HO
OH
O
O
O
Compound A
Compound B
Compound C
C-triple-C
stretch
O
Compound D
C-O stretch
sp C-H
stretch
This spectrum belongs to: Compound D
Reason: The spectrum shows a C-C triple bond stretch at 2100 cm-1, and more importantly, an
sp-hybridized C-H stretch at 3300 cm-1. Only compound D has a hydrogen attached to the triple
bond. This peak differs from an alcohol peak (which would show up at the same place) because
it is not broad, like a hydrogen-bonded alcohol peak would be.
Exam 1
Fall 2008
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Chemistry& 241
Clark College
C=O stretch
C-O stretch
This spectrum belongs to: Compound B
Reason: The carbonyl stretch at 1720 cm-1 narrows it down to compounds A or B. however, the
C-O stretching frequency at 1190 cm-1 indicates an ester, not a ketone.
O-H
stretch
This spectrum belongs to: Compound C
Reason: The large OH stretch between 3500-3200 cm-1 makes it obvious! The C-C triple bond
stretch does not show up, since the molecule is symmetric.
8. Draw two examples of a molecule (for each condition) that has the formula C6H12 and: [6]
a) That exhibits angle strain (or ring strain). (provide two examples)
Three or four-membered rings only! Five and six-membered rings do not show angle (ring)
strain.
b) That exhibits a peak in the IR between 1600 – 1680 cm-1. (provide two examples)
An IR peak at 1600-1680 cm-1 indicates an alkene. Any 6-carbon alkene would work.
Exam 1
Fall 2008
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Chemistry& 241
Clark College
9. For the molecule 2-isopropyl-5-methylcyclohexanol, draw the lowest possible energy chair
conformer for the molecule, then translate that structure to a “flat hexagon” structure with wedges
and dashes to indicate the relative positions of the 3 substituents. [6]
"down"
H3C
OH
H
H
"down"
OH
OH
"up"
H
The lowest energy conformer has all groups in equatorial positions.
10. Draw a line structure for 1-bromo-2-methylbutane, and then draw and label the following three
Newman projections for the structure: The LOWEST energy conformation, the SECOND LOWEST
energy conformation, and the HIGHEST energy conformation. Your Newman projections should be
“looking” down the C1-C2 bond. [10]
LOWEST
SECOND LOWEST
Br
HIGHEST
Br
H
CH3
H
H
H3CH2C
H
H
H
H3CH2C Br
Br
CH3
CH2CH3
H
H
H3C
CH3
With only one hydrogen on carbon 2, all of the
staggered conformations will have a gauche
interaction with the bromine on carbon 1. The
lowest energy conformation has the bromine
in a gauche interaction with the methyl group,
which is smaller than the ethyl group.
H
The high energy conformers are
always eclipsed conformers. The
highest energy conformer will have
the two largest groups (the bromine
and the ethyl) eclipsed.
11. Which of the following molecules has the lowest boiling point? [2]
More branching!
Exam 1
Fall 2008
Page 5 of 6
Chemistry& 241
Clark College
12. Nitroamines are common functional groups in highly reactive molecules (such as plastic
explosives). The sample structure below has all electrons represented. For the structure given,
assign formal charges to the atoms that need it, and then draw any significant resonance structures
for the molecule. [6]
H3C
O
N
H3C
H3C
N
O
N
O
H3C
N
O
Another structure can be drawn with a double bond between the nitrogens, but is has extra formal
charges, therefore it is not a significant structure.
13. Completely explain why the staggered conformation in ethane is more stable (lower energy) than
the eclipsed conformation in ethane. Use words and/or pictures in your explanation. [6]
H
H
H
The staggered conformation gives the largest dihedral angle
between neighboring groups, minimizing torsional strain and steric
hinderance between the C-H bonds on carbon 1 and carbon 2.
H
H
H
H
H
H
H
H
H
The staggered conformation also allows for overlap between a
C-H bond on one carbon and the !* orbital on the other carbon,
allowing the electron density to be delocalized into a larger area.
H
14. In an alkyne, the triple bond consists of: [2]
a) Two sigma bond formed from p orbitals and one pi bond formed from sp-hybrid orbitals on each
carbon.
b) One sigma bond formed from hybrid orbitals and one pi bond from p orbitals on each carbon.
c) Three bonds formed from the pairs of px, py, and pz orbitals on each carbon.
d) One sigma bond formed from hybrid orbitals and two pi bonds from p orbitals on each
carbon.
Exam 1
Fall 2008
Page 6 of 6