1
CHEMISTRY 241A (5-6)
EXAM 4
December 2, 2005
DOLLINGER
1. ____
(33)
2. ____
(16)
3. ____
(18)
4. ____
(18)
5. ____
(15)
B ____
(2)
Name:___KEY_____________
ID#:______________________
Total _____ (102)
GOOD LUCK!
YOU SHOULD HAVE 6 PAGES!!!
Bonus (2 pts): What is the rate equation for the following transformation?
OTos
HOAc
R=k [
OAc
]
OTos
2
1. (33 pts) Answer the following questions. If the answer requires you to draw a
product or starting material be sure to clearly indicate stereochemistry.
(a) (5 points) Predict the major alkene product of the following E1 reaction.
CH3CH2 CH3
HOAc
CH3CHCBr
heat
CH2CH3
(b) (9 points) In the space provided indicate whether each reaction is an oxidation,
reduction, or neither.
Oxidation, Reduction,
or Neither
I
(i)
LiAlH4
Reduction
(ii)
SOCl2
Neither
OH
Cl
H3O+
(iii)
Neither
OH
(c) (5 points) Predict the major product of the following reaction.
NBS
hv
+
Br
Br
(d) (5 points) Draw the structure of the starting material for the sequence of reactions
shown below.
OH
H2SO4
heat
or
OH
1. BH3
CH3
SOCl2
2. H2O2, KOH
Cl
3
(e) (9 points) Using the partial Fischer projections below draw the product of the
reactions.
TosCl
pyridine
CH3
NaOCH3
H3CO
H
CH2CH3
CH3
PBr3
S-2-butanol
Br
H
CH2CH3
CH3Br
K
CH3
H
OCH3
CH2CH3
2. (16 pts) Provide a sequence of reactions to carry our the following transformations.
You may use any needed organic or inorganic reagents. More than one step will
be needed. Give necessary reagents and the product of each individual step.
???
NBS
(CH3)2CuLi
Br
Br
KOH
NBS
4
3. (18 pts) The synthetic sequences below are unlikely to occur as written. Describe
what the flaw in the reaction is as written (10 words or less) and draw the correct
product of the reaction in the space provided or write no reaction if the reaction does
not proceed at all. (McMurray 11.34)
Correct Product or
No Reaction
(a)
O
OTos
K+ -OC(CH3)3
Reaction will not proceed as written because:
Base too bulky to act like nucleophile for SN2
(b)
F
NaOMe
OMe
NR
Reaction will not proceed as written because:
F - is not a good leaving group
(c)
HO
PBr3
Br
Reaction will not proceed as written because:
PBr3 goes by SN2 mechanism and SN2 will not occur on a 3o site
NR
5
4. (18 pts) The mesylate of (2R, 3S)-3-methyl-2-pentanol undergoes E2 elimination
on treatment with sodium ethoxide to yield 2-phenyl-2-butene. (McMurray 11.47)
CH2CH3
CH3
OMs
NaOEt
H3CH2CC
H3C
CHCH3
CH3
(a) Using the partial Fischer projection below draw the correct configuration of the
starting material, and using the partial alkene frame-work below draw in the correct
stereoisomer of the product of the reaction.
CH3
MsO
H
H
Et
H3C
NaOEt
Et
H
CH3
CH3
(b) Using the partial Newman projection below draw the correct conformation of the
mesylate of (2R, 3S)-3-methyl-2-pentanol (looking down bond 2-3) from which the
elimination would take place.
Et
CH3
MsO
H
H
Me
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5. (15 pts) Provide the mechanistic symbol (SN1, SN2, E1, E2) by which the following
reactions proceed.
(a)
Na+ I-
CH3Br
(b)
DMSO
CH3
CH3
H3C
C
SN2
CH3I
CH3OH
Br
H3C
C
OCH3
SN1
CH3
CH3
(c)
OTos
E2
KOtBu
HOtBu
(d)
Cl
(e)
CH3
H3C
C
CH3
EtOH
E1
CH2
CH3ONa
E2
Br
H3C
CH3