Download CH334E2_01

Ch 334
Midterm #2
November 21, 2001
1.
Name_____________________________________
(4 pts) Consider the properties of the following compounds:
NAME
FORMULA
BOILING PT (oC)
MOLECULAR
WEIGHT
Ethane
CH3CH3
-88.2
30
Fluoromethane
CH3F
-78.6
34
Methanol
CH3OH
+64.7
32
Why does methanol boil so much higher than ethane or fluoromethane even though they all
have nearly equal molecular weights?
2.
(2 pts) Consider the structure shown below. Is the conformation given a cis or trans
isomer?
H
H
CH3
CH3
3.
(2 pts) Complete the formula for the most stable conformation of cis-1,3dimethylcyclohexane. You only need to draw in the groups that are at positions 1 & 3 as
was done in question #2.
page 2
4.
(2 pts) Consider the molecule shown at the right:
(a) Draw the other chair conformation of this molecule.
CH3
(b) Circle the conformation above that is present in greater concentration in the equilibrium
mixture.
5.
(6 pts) The following names are incorrect IUPAC names. Draw the structure implied by
this name, indicate why the given name is incorrect and write the correct name for each
structure.
(a) 2-methylcyclohexene
(b) 1,2,2-trichloro-4-pentene
6.
(4 pts) In the equilibrium below, the strongest acid is __________________.
H2SO4 + (CH3)2CHOH
 HSO4- + (CH3)2CHOH2+
2
page 3
7. (6 pts) Give IUPAC names for the following compounds:
(a)
CH2CH2CH(CH 3)2
CH3CH2CH2CHCHCH3
OH
_________________________________________________
(b)
CH3
H
H
CH2
CH3
H
CH2
H
H
H
_________________________________________________
8.
(6 pts) Circle any of the alkene structures shown below which have geometric isomers.
CH2CH3
CH3
C
C
H
CH3
9.
C
C
C
CH2Br
Cl
CH2I
BrH2C
Br
H
IH 2C
C
CH2Br
(6 pts) Assign E/Z configurations to each of the following alkenes.
CH2CH3
CH3
C
H
CH2Cl
H
C
C
H
CH3CH2
CH3
BrCH2
C
C
COOH
CH3
C
CH2CH3
3
page 4
_______
_______
_______
10. (6 pts) Give the alkenes that can form from acid-catalyzed dehydration of the following
alcohols. If more than one product can form, identify the products as major or minor.
(a)
CH3
OH
(b)
(CH3)2CHCH2OH
11. (4 pts) Although you have not seen reactions involving the following species, your
background knowledge concerning nucleophiles and electrophiles is enough to answer this
question. Indicate whether the following species would be expected to react as nucleophiles
or electrophiles. Justify your choice.
(a) :Cl+ __________________ Reason:
(b) (CH3)3C:- __________________ Reason:
12. (8 pts) Identify the Species I and II as electrophiles (E) or nucleophiles (Nu) in the reactions:
Species I
Species II
(a)
(CH3)2O:
+
_______
(b)
:CN:_______
B(CH3)3
---------> (CH3)2O-B(CH3)3
_______
+
CH3Br
---------->
H3C:CN + :Br:-
________
4
page 5
13. (16 pts) Circle the compound in each group that fits the description provided.
(a) Has the lowest Heat of Hydrogenation
(b) Has the highest Heat of Combustion
(c) Is lowest in energy.
CH3
CH3
CH2
(d) Is most stable.
CH3
CH3
CH2
5
page 6
14. The reaction of tert-butyl bromide with ethanol shown below is termed a solvolysis reaction
and gives the products formed.
Br
+ HOCH2CH3
55oC
OCH 2CH 3
+
tert-butyl ethyl ether
72%
+ CH3CH2OH2Br 2-methylpropene
28%
ionized form
of HBr in
ethanol
Experiment shows that when the concentration of t-butyl bromide is doubled without
changing the amount of ethanol, the rate of reaction doubles. When the concentration of
tert-butyl bromide is held constant and the concentration of ethanol doubled, no change in
the reaction rate is observed.
(a) (6 pts) Draw a mechanism showing how 2-methylpropene forms that is consistent with
the kinetic data presented above. DO NOT COMBINE STEPS IN YOUR
MECHANISM. You must use arrows to show all electron movement.
(b) (4 pts) Draw a potential energy diagram depicting the intermediates and transition states
involved in the reaction.
6
page 7
(c) (2 pts) What is the rate determining step of the reaction?
15. (6 pts) Draw the most stable chair conformation for the two molecules shown below.
One of these stereoisomers undergoes elimination on treatment with sodium ethoxide in
ethanol much more readily than the other. Circle the one which reacts faster.
CH(CH 3)2
(a)
H3C
Cl
CH(CH 3)2
(b)
H3C
Cl
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page 8
16. (10 pts) Complete the following reactions by showing the MAJOR organic product.
H 3C
(a)
Br2
H3C
CH3
ultraviolet light
CH3
(b)
(c)
(d)
PBr3
(CH3)2CHCH2OH
HBr
(CH3)3COH
Na
CH3CH2OH
H3C
CH3
NaOCH2CH3
(e)
Br
8
page 9
Bonus Question (10 pts):
Dehydration of cyclohexylmethanol in the laboratory was found to yield three different
alkene products. One of these products was cycloheptene. Draw a mechanism that clearly
shows how this product forms.
OH
CH3
CH2
H2SO4
heat
+
+
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