CHEM 301 - Dr. Hartel
Winthrop University
Self Evaluation 5
1. Resonance
Draw Lewis structures for all of the remaining resonance structures for each of the following
molecules in the boxes provided. Circle the most stable structure for each system.
H
H
O
H
C
H
C
C
H
O
C
H
H
H
H
H
H
O
C
C
C
C
H
H
H
H
O
C
H
H
H
C
C
C
H
C
C
H
H
H
C
C
C
C
H
C
H
H
H
H
H
C
H
H
1
O
H
H
H
H
C
H
H
CHEM 301 - Dr. Hartel
Winthrop University
Self Evaluation 5
2. Reactions
a. Draw the major product or products of each of reaction in the boxes provided. If multiple
organic products are equally likely, show each. For stereoselective reactions, be certain that your
structures clearly indicate stereochemistry.
Br
HBr
(benzene does not
undergo addition)
2o benzylic carbocation is more stable
O
CH3
C
C
CH2CH3
H2O, H+
+
Hg2+
O
H
C
C
CH2CH3
HCl
(1 equiv)
Cl
OH
H2O (1 equiv)
H+, warm
Br
Br2 (1 equiv)
cold
Br
2
CHEM 301 - Dr. Hartel
Winthrop University
Self Evaluation 5
b. Provide the reagents necessary to perform the following reactions in the boxes provided. Be
explicit when showing multi-step reactions.
H2, Pd/C
H3C
C
C
CH2CH3
C
C
H
O
H2O, H+
CH3
C
C
H
1) disiamylborane
2) H2O2, H2O, HO-
H
O
Li, NH3 (liq)
-78 oC
H3C
C
C
CH2CH2CH3
C
C
H
C
H
H2
Lindlar's Pd
CH3CH2
H3C
CH2CH2CH3
H
H
C
CH2CH3
CH3CH2
3
C
C
CH2CH3
CHEM 301 - Dr. Hartel
Winthrop University
Self Evaluation 5
3. Mechanisms
a. Draw complete arrow pushing mechanisms for the following reaction.
H
H3C
C
C
CH3
O
H
C
H
C
O
H3C
H
H
H
H
H
H
O
H
H
O
C
O
H
H
H
C
C
H3C
CH3
O
H
H3C
O
H
C
CH3
H
O
H
H3C
CH3
O
H
C
H
C
H3C
O
C
H
H
H
CH3
C
H
H
H
CH3
b. Draw a complete arrow pushing mechanisms for the following reaction. Circle the
thermodynamic product. Label each product as “1,2-addition” or “1,4-addition”.
H
H
H
Br
Br
Br
1,2 addition
4
Br
1,4 addition
CHEM 301 - Dr. Hartel
Winthrop University
Self Evaluation 5
4. Synthesis
Propose plausible syntheses for each of the products shown starting with the molecule provided.
a.
C
H
H
C
C
C
H
OH
1) NaNH2
H
H3CH2C
2) CH3CH2Br
H3CH2C
H
C
C
H
C
C
H2, Lindlar
H
H3CH2C
1) BH3
H
2) H2O2, HO-, H2O
H
C
H
H
C
OH
H
b.
Br
H2C
H2C
HBr
CH2
CH2
H
Br
C
C
Na
H
Br
H2
HBr
Lindlar's Pd
5
C
C
CHEM 301 - Dr. Hartel
Winthrop University
Self Evaluation 5
5. Application of Concepts
a. Two alcohols are shown below. Cyclohexanol (pka = 16) is produced as a precursor in nylon
synthesis. Phenol (pka = 10) was used as an antiseptic and is still used in embalming cadavers
for use in “gross anatomy” labs in medicals schools. Explain the large difference in the acidities
of these two compounds.
OH
OH
cyclohexanol
phenol
Acidity is related to conjugate base stability. Phenol, the stronger acid, must have a more stable
conjugate base. This can be seen when the conjugate bases are drawn. One would expect the
conjugate base of phenol (“phenoxide”) to have resonance. This in-and-of itself means little, as
phenol itself also has resonance. However, the charge in phenoxide ion is stabilized by spreading
out the charge across four atoms, as can be seen in the four additional resonance structures.
Cyclohexanol’s conjugate base has no resonance stabilization, and thus the charge is essentially
isolated on the one atom (oxygen). Phenol’s conjugate base is more stable, due to resonance
spreading out the charge, than cyclohexanol’s conjugate base. This makes phenol more acidic.
O
O
O
O
O
O
vs.
b. When 3-propoxy-1-propene is analyzed using mass spectrometry, a very large peak at 41 amu
is observed. What is the structure of this fragment ion, and why is it so prevalent in the mass
spectrum?
Determining the possible fragments shows two α-cleavage fragments and two C-O bond cleavage
fragments. The C-O cleavage on the right gives the mass of interest (41). This is a resonance
stabilized allylic cation, and thus will be prominent in the MS due to its extra stability.
O
ag
e
cle
ea
v
O
e
m/z = 71
C-
O
cl
ag
av
O
-c
lea
vag
e
m/z = 100
C-
ge
ava
e
l
c
-
O
m/z = 73
m/z = 41
m/z = 43
6