Chem 240
Exam #1
Name___Key____________
September 25, 2013
CLOSED BOOK EXAM - No books or notes allowed. All work must be shown for full
credit. You may use a calculator.
Question
1(18 )
Credit
2(21)
3(9)
4(12)
5(6)
6(18)
7(16)
TOTAL
1) Please name or draw the structure of the following compounds.
H
CH3
H
Bicycle [3,2,0] heptane
CH3
H
C2H5
H3C H
3-methyl pentane
CH3
Cl
E-chloro-1,2-dimethylcyclopentane
2,2-dimethyl-4-isopropylheptane
Br
H3C
(CH3)2CHCH2CH2Cl
3-methylchlorobutane
C
CH3
CH3
2-bromo-2-methylpropane
2) Please draw the rotational energy diagram for the rotation of 2,3 dichloropentane
around the C2-C3 bond.
6
5
Energy
4
3
2
1
0
60
120
180
240
300
360
Draw the molecule below, convert it to a Newman projection and then rotate it about the
C2-C3 bond. Based on your rotations, draw the energy diagram above.
Cl
Cl
Cl
C
C2H5
Cl
H
HH
H
6
Cl
H
Cl
C
C2H5
H C2H5
2
C2H5
C
Cl
C2H5
Cl
H
4
H
C
H
H
H Cl
3
5
Cl
C2H5
Cl
Cl
Cl
Cl
Cl
Mirror Image
Cl
Cl
Cl
C
Cl
H
1
3) Please draw all of the isomers of C3H6Cl2
Cl
C
Cl
Cl
4) Please answer the following questions concerning the molecule given below.
O3
H
N
H
N
a) How many pi and sigma bonds are in this compound?
C
C
4
20 σ
2
N
1
C
N
N
7π
b) What is the hybridization on the following atoms;
1
2
3
4
sp3
sp2
sp2
sp
5) Please draw the most stable boat configuration of trans 1,3 dimethylcyclohexane.
H3C
CH3
6a) Please write down all the steps in the mechanism of the free radical chlorination of
2-methylpropane.
Chain Initiation
light
Cl2
2 Cl
Chain Propagation
H
Cl
H3C
C
CH3
HCl
+
H3C
C
CH3
CH3
CH3
Cl
H3C
C
Cl2
CH3
H3C
C
CH3
+ Cl
CH3
CH3
Chain Termination
Cl
Cl
Cl2
Cl
Cl
H3C
C
H3C
CH3
C
CH3
CH3
CH3
CH3
H3C
C
CH3
CH3
H3C
C
CH3
CH3
H3C
C
CH3
H3C
C
CH3
CH3
6b) What is the ratio of products formed in the free radical chlorination of bicyclo [2,2,0]
hexane?
x = 280/3.8 = 73.68% 2°
7a) What are the advantages of using bromine instead of chlorine in a free radical
halogenation?
a) Higher yields
b) Fewer by-products
7b) What happens to the boiling point of an alkene when one of its bonds changes from
cis to trans and why?
A cis bond puts a kink in the chain and makes it difficult to stack. A trans bond
removes the kink and makes it easier to stack so there are more interactions
between the molecules. The boiling point goes up. It is more difficult to boil.
7c) How does branching affect the boiling point of a compound and why?
Branching makes it difficult for the molecules to stack so there is less interaction
between them which lowers the boiling point.
7d) What is the primary intermolecular bonding force in each of the following
compounds?
2-butanone
H-Bond
Dipole-Dipole
Dispersion
trans 1,2-dichloroethene
H-Bond
Dipole-Dipole
Dispersion
C12H25COOH
H-Bond
Dipole-Dipole
Dispersion
Cyclopentanol
H-Bond
Dipole-Dipole
Dispersion