Organic Chemistry I
CHM2210
Exam 2
Fall 2006
KEY
I. Fill in the Blanks (Each Blank = 1 Points)
1.
A 50:50 mixture (by moles) of a pair of enantiomers is called a racemic mixture.
2.
A compound has 3 chiral carbon atoms. What is the maximum possible number of
stereoisomers this compound can have? 8
3.
A mixture of enantiomers that contains a 50% enantiomeric excess (is 50% optically pure)
of the (R) isomer, contains 75% or the R and 25% of the S forms.
4.
Comparing isopropyl alcohol and 2-methyl-2-butanol, only 2-methyl-2-propanol contains a
tertiary carbon atom.
5.
(True/False) Single bonds between the atoms of cyclohexane are normally capable of free
rotation. False
CH3
6.
How many chiral carbons are in the compound β-cadinene. 3
H3C
CH(CH3)2
7.
The specific rotation [α]D20 of a compound is a function of observed rotation, concentration,
and path length. (Hint -The components of the formula used to calculate it.)
8.
Enantiomers have almost all the same physical properties. One physical property that
distinguishes two enantiomers is that they rotate PPL in equal but opposite directions.
9.
What is the stereochemical relationship between (2R,3R,4R)-trichlorohexane and
(2S,3S,4R)-trichlorohexane? They are diastereomers.
10. (True/False) None of the cis-dimethyl isomers of cyclohexane are chiral. True
11. Why does a catalyst speed up a chemical reaction? It lowers the energy of activation of the
reaction.
12. Bond dissociation energies are the energies associated with the homolytic (homolytic or
heterolytic) cleavage of a bond between two atoms.
II. Write IUPAC Names For the Following Compounds. Use R and S When Necessary.
(11 Points)
H
CHO
Cl
H3C
CH3
HO
H
CH2OH
(R)-4-chloro-2-methylhexane
(S)-glyceraldehyde
1,4-dimethylcyclohexane
CH3
H3C
C
CH3
CH3
H2C
CH3
Cl
CH3 CH3
CH2 CH CH CH CH CH3
CH3 CH CH3
(1S,2S)-1-methyl-2-(dimethylethyl)cyclopentane
5-chloro-2,3-dimethyl-4-(methylethyl)octane
III. Draw the Structures of the Following Compounds. Be sure to include all hydrogens
when drawing structural formulas and leave them off of bond-line structures.
(7 Points)
CH3
Cl
HO
H3C
___________________________
______________
___________________________
trans-1,3-dimethylcyclobutane
isobutyl alcohol
1-chlorobicyclo[2.2.2]octane
IV. Multiple Choice – Circle the best answer (2 Points Each)
_____ 1.
Which of the following is a propagation step in the free-radical bromination of
methane?
a. CH3· + Br·
→
CH3Br
b. Br2 + light → 2Br·
c. CH3· + Br2 → CH3Br + Br·
d. CH3· + CH3· → CH3CH3
e. Br· + Br· → Br2
_____ 2.
a.
b.
c.
d.
e.
Fluorine is more reactive than chlorine in these reactions.
Bromine is more selective than chlorine.
The reactions require light, heat, or other free-radicals to proceed.
Brominations are faster than chlorinations.
These reactions are irreversible.
_____ 3.
a.
b.
c.
d.
e.
In a carbon free radical, the single unpaired electron resides in?
an sp2 orbital.
an sp3 orbital.
an s orbital.
a p orbital.
None of these.
_____ 5.
a.
b.
c.
d.
e.
Alkanes are noted for their (choose one)
high reactivity.
toxicity.
intense odor.
lack of reactivity.
water solubility.
_____ 4.
a.
b.
c.
d.
e.
Which of the following is NOT true of free-radical halogenation reactions?
Hyperconjugation is MOST useful for stabilizing which of the following?
pentyl radical
tert-butyl radical
isopropyl radical
ethyl radical
methyl radical
_____ 6.
a.
b.
c.
d.
e.
cis-1,3-Dibromocyclohexane is represented by structure(s):
I
II
III
I & II
II & III
Br
a.
b.
c.
d.
e.
Br
Br
H
II
III
The preferred conformation of cis-3-tert-butyl-1-methylcyclohexane is the one in
which:
Which of the following has the HIGHEST heat of combustion per CH2 group?
I
II
III
IV
All have the same
∆H per CH2.
_____ 9.
a.
b.
c.
d.
e.
Br
H
the tert-butyl group is axial and the methyl group is equatorial.
the methyl group is axial and the tert-butyl group is equatorial.
both groups are axial.
both groups are equatorial.
the molecule exists in a boat conformation.
_____ 8.
a.
b.
c.
d.
e.
H
H
H
Br
I
_____ 7.
Br
H
I
II
III
IV
V
I
II
III
IV
What structure represents the most stable conformation of cis-1,3dimethylcyclohexane?
CH3
H
H
CH3
CH3
H
CH3
H
H3C
H3C
H I
H
II
III
H
H
H
CH3
H3C
CH3
H3C
H
IV
V
_____ 10.
a.
b.
c.
d.
e.
C3H7Cl < C5H12 < C2H6 < C4H9OH < C20H44
C2H6 < C5H12 < C20H44 < C3H7Cl < C4H9OH
C4H9OH < C2H6 < C5H12 < C3H7Cl < C20H44
C2H6 < C5H12 < C3H7Cl < C4H9OH < C20H44
C20H44 < C5H12 < C4H9OH < C3H7Cl < C2H6
_____ 11.
a.
Which choice correctly lists the following compounds in INCREASING order with
respect to their boiling points? C2H6 , C20H44 , C3H7Cl, C4H9OH, and C5H12
An alkane, C6H14, reacts with chlorine to yield four constitutional isomers with the
formula C 6H 13Cl. The structure of the alkane is:
CH3 CH2 CH2 CH2 CH2 CH3
d.
CH3 CH2 C CH3
CH3
b.
CH3
CH3 CH2 CH2 CH CH3
CH3 CH3
CH3
c.
a.
b.
c.
d.
e.
e.
CH3 CH2 CH CH2 CH3
_____ 12.
CH3
CH3 CH CH CH3
Which of the following correctly represents cyclopropylcyclohexane?
I
II
III
IV
None are correct
I
II
III
IV
_____ 13.
a.
b.
c.
d.
e.
cis-1,4-Di-tert-butylcyclohexane
trans-1,4-Di-tert-butylcyclohexane
cis-1,3-Di-tert-butylcyclohexane
trans-1,2-Di-tert-butylcyclohexane
None of these
_____ 14.
a.
b.
c.
d.
e.
The twisted boat conformation is the preferred conformation for this compound.
I
II
III
IV
V
_____ 15.
(R)-2-Chlorobutane is represented by:
CH3
Cl Cl
H3C
CH2CH3
CH2CH3
I
CH2CH3
Cl
CH3 H3C
III
I
II
III
IV
V
H
CH2CH3
IV
d.
e.
V
constitutional isomers.
None of these
The molecules shown are:
Not chiral
H
H
Br
H
Br
H
Cl
Cl
H
CH3
a.
b.
c.
d.
e.
H
Hexane and 3-methylpentane are examples of:
constitutional isomers.
enantiomers.
diastereomers.
identical.
None of these
_____ 17.
CH2Cl
H
H
a.
b.
c.
d.
e.
Cl
H3C
CH2CH3
II
a. enantiomers.
b. stereoisomers.
c. diastereomers.
_____ 16.
H
CH3
CH3
Which compound does not possess a plane of symmetry?
CH3
H
OH
HO
H
OH
H
CH3
I
OH
CH3
H
CH3
OH
II
H3C
H
OH
H
H
CH3
CH3
H
CH3
OH
OH
III
IV
_____ 18.
a.
b.
c.
d.
e.
The specific rotation is 0°.
There are one or more planes of symmetry.
A single molecule is identical to its mirror image.
More than one stereocenter must be present.
The stereochemical labels, (R) and (S), must be identical for each stereocenter.
_____ 19.
a.
b.
c.
d.
e.
3
5
6
7
8
_____ 20.
a.
b.
c.
d.
e.
Which statement is not true for a meso compound?
CH3CHBrCHBrCHBrCH 3 is the generalized representation of what number of
stereoisomers? (Hint – Draw the structural formula)
(2R,4R) (2S,4S) (2R,4S) (meso) carbon #3 is not chiral
Which of the following is a meso compound?
Br
Br
I
II
III
IV
V
a.
b.
c.
d.
e.
Br
Br
Br
Br
Br
I
_____ 21.
Br
Br
Br
II
III
IV
Which of the following represents bicyclo[4.1.1]octane?
I
II
III
IV
V
I
II
III
IV
_____ 22.
a.
b.
c.
d.
I
II
III
IV
V
V
Which is the correct structure for (R)-bromofluoroiodomethane?
Br
H
I
H
F
I
I
F
H
Br
Br
II
H
F
I
Br
III
I
F
IV
V.
Using a 3-Dimensional Representation, Draw the structures of the compounds below.
(6 Points)
CH3
H
OH
H
Br
H
Br
CH3
(R)-2-butanol
using a bond-line formula
(2R,3S)-2,3-dibromobutane
using a Fischer Projection
CH3CHOHCH2CH3
CH3CHBrCHBrCH3
VI. Complete the following equations by showing the product(s) of the reactions. If no
reaction occurs write N.R. for No Reaction. ( points)
CH3
CH3
1.
Br2
Br
300°
F
F2 (limit)
2.
F
light
F
F
H2
3.
Pt
4.
5.
CH3
I2
CH3 CH CH3
light
NO REACTION
F2
F
light
(Major product only)
12 ways to make 1°
only 2 ways to make 3°