Name:
ORGANIC CHEMISTRY I (CHEM 323)
EXAM 1
September 22, 2009
There are six pages, FOURTEEN questions, and a total of 118 points in this exam, which gives an extra
18 points on top of that required for a “perfect” paper. Please read each question carefully and possibly
more than once. Good luck…
(6)
1.
In the illustration of acetylene (C2H2) shown below name each of the orbitals pointed by
an arrow.
sp
s
(5)
2.
Using the carbon skeletons (with the equatorial and axial bonds drawn) construct two
different dimethyl substituted cyclohexanes with the same carbon connectivity, Make
sure that the two structures cannot be converted into each other by a “ring flip”
CH3
CH3
CH3
or any other cis and trans
CH3
(21)
3.
Circle the best correct answer (only one) for each of the multiple choice questions given
below:
3.1.
Which of the following molecules can function as a Lewis base?
Note that formal charges are not shown
CH3
H3C
N
O
(1)
3.2.
CH3
H3O
(2)
(3)
(4)
What is the relationship between the two substituted cyclohexanes given?
CH3
CH3
(1) Different conformations
(2) Constitutional isomers
(3) cis/trans isomers
(4) There is no isomeric relationship between the two molecules given above
3.3.
What is the relationship between the following
(5)
(6)
(7)
(8)
3.4.
Different conformations
Constitutional isomers
cis/trans isomers
There is no isomeric relationship between the two molecules given above
Complete combustion of cis-1,3-dichlorocyclohexane and
trans-1,3-dichlorocyclohexane yields different
(1) products (2) amounts of heat of reaction
(4) all three answers are correct
3.5.
(3) amounts of oxygen
Among the carbon containing compounds below in which one does carbon bear
the greatest partial positive charge?
(1) methane (CH4)
(2) chloromethane (CH3Cl)
(3) methyllithium (CH3Li)
(4) carbon never bears partial positive charge
Page 2
3.6
Place the anions below in order of stability (most stable first, least stable last)
H
H
N
C
O
H
(A)
(B)
(1) A>B>C
3.7.
(2) B>A>C
(C)
(3) C>A>B
(4) A>C>B
(5) C>B>A
Which of the following molecules is the least volatile (one with the highest b.p.)?
O
(1)
(2)
(3)
(4)
(6)
4.
The structures in question 3.6. can be converted into species which may function as
acids. Write the structures of the “acids” in order of strength (strongest acid first)
O H
H
N
H
H
C
H
H
weakest acid
strongest acid
(4)
5.
Explain your choice of answer for 3.7.
The ketone in 3.7, (4), is more polar than the other three compounds, and it experiences
dipole-dipole interactions, which are stronger intermolecular forces than van der Waals
forces; thus the ketone is the least volatile of the molecules in 3.7 and has the highest
boiling point.
(5)
6.
Draw the skeletal structure for an isomer of C8H18 in which there are no secondary
carbons.
or
Page 3
(4)
7.
Identify all the carbons in the following molecule, which is/are equivalent to the carbon
circled.
(9)
8.
Draw a skeletal structure of the molecule whose Newman Projection Representation is
given below.
CH3
C(CH3)2CH2CH3
H3C
H
CH(CH3)2
CH2
CH3
6.1.
Name the molecule according to the IUPAC rules of naming:
4-ethyl-2,3,4,5,5-pentamethylheptane
(7)
9.
Propose a molecule (write a structure), in which the electron configuration of one of the
carbons is 1s2 2s2 2p2 (no hybridization). Circle below any of the characteristics which
may apply to this molecule (more than one characteristic may be applicable).
H
C
H
(a) molecule is very reactive
(b) molecule is unreactive
(d) molecule cannot exist
(b) molecule may function as an electrophile
(d) molecule may function as a nucleophile
(12)
10.
Complete the reactions below and identify the structures of the missing products. Use
curly arrows to show electron transfers, bond formations, and/or bond cleavages. Show
all formal charges (if any).
Cl
Cl
10.1.
+
Al
Al Cl
Cl
Cl
Cl
O
10.2.
O
O
H
+
O
O H
Page 4
+
H2O
(10)
11.
The following potential energy diagram shows the rotation of 1,2-dibromoethane. Draw
in Newman Projection representations the conformations represented by A, B, and C in
the potential energy diagram. Indicate which is which.
B
C
A
0o
60o
120o
Br
H
H
H
H
Br
(A)
180o
240o
300o
H Br
360o
Br
Br
H
H
H
H Br
H
H
H
(B)
(C)
(5)
12.
Draw the following in a stable chair conformation:
C(CH3)3
H3C
C(CH3)3
CH3
cis
The tert-butyl group cannot acquire an axial orientation (1,3-diaxial interactions would be too
unfavorable)
Page 5
(19)
13.
Nitromethane, CH3NO2, has a pKa of 10.2 (more acidic than an alcohol).
13.1.
Write the Lewis structure of nitromethane. Indicate all formal charges (if any)
H
O
H C N
O
H
13.2.
Write the Lewis structure for the conjugate base of nitromethane
H
O
C N
O
H
13.3.
Show how you can utilize resonance theory to demonstrate that nitromethane is
indeed acidic enough
H
O
C N
O
H
H
O
C
H
N
O
the lone pair of the conjugate base can delocalize
into the molecule through resonance, thus can exist
as a stable, i.e. weak conjugate base, which indicates
that the corresponding undisccociated acid is relatively strong
13.4.
Draw the Lewis structure of methyl nitrite, a constitutional isomer of
nitromethane, and show why methyl nitrite is not acidic.
H
H C O N O
H
No possibility for the delocalization of
the conjugate base lone pair through
delocalization as in 13.3.
Page 6
H
C O N O
H
(5)
14.
“Molecules of the Week” Questions:
Answer ONE of the questions (14.1 OR 14.2) below:
14.1.
O
Draw the structure of aspirin. Identify one of the functional groups on the
molecule (if you cannot remember the full structure of the molecule, you can still
get credit by writing the name and an illustrative (generic) structure for one of its
functional groups.
O
O
Carboxylic acid
OH
14.2.
Write the name (or if you wish, the structure) of the product of the following
reaction:
Morphine
+
acetic anhydride
Page 7
heroin