Organic Chemistry Ⅰ
2nd Examination
Dec. 13, 2003 9:00 a.m.-11:00 a.m.
Ⅰ. Each of the following problems has five statements. Each problem is worth
four points. Any wrong guess will cost you one extra point. (60 points)
1. How many stereoisomers (enantiomers and diastereomers, if any) of the following
are possible?
HO OH
H
H
O
O
OH
HO
(A) 2
(B) 3
(C) 4
(D) 5
(E) 6
2. The molecular formulas and 13C NMR chemical shifts (in ppm) of a hydrocarbon
are given below. The splitting pattern of each signal, taken from the
non-decoupled spectrum is given in parentheses. What is the structure?
(Hint: “t” means the 13C signal splits into a triplet due to coupling with the two H
nuclei. “d” means doublet.)
C7H10: 25.2 (t), 41.9 (d), 48.5 (t), 135.2 (d)
(A)
(B)
(D)
(E)
(C)
3. Indicate the reagents required to achieve the following transformation:
H
CH3O
CH3
Br
H
CH3
H
CH3O
?
1) NaF
NaCN
(A)
(B)
1) NaOH
2) KCN
(C)
2) KCN
1) NaOMe
1) NaI
(D)
CH3
CN
H
CH3
2) NaCN
(E)
2) HCN / light
4. An unknown compound has been isolated in pure form and found to exhibit []D =
+ 15∘ (c = 4 g/ml, CH2Cl2). Which of the following might be the structure of
the compound?
H3C H
H3C
(A)
(B)
H
CH3
CH3
H
C
(C)
H
CH3
CH3
OH
(E)
OH
(D)
CH3
CH3
H3C H
5. Which of the haloalkanes below would you expect to exhibit the fastest rate of the
following solvolysis reaction?
H2O
RX
ROH + HX
acetone
(A) CH3CH2Br
(B) CH3Br
(C) (CH3)3CBr
Br
(D) CH3CHBrCH3
(E)
6. Name the following compound:
Cl
Br
(A) (1S, 2S, 5R)-1-bromo-2-isopropyl-5-chlorocyclohexane
(B) (1R, 2R, 5R)-1-bromo-2-isopropyl-5-chlorocyclohexane
(C) (1S, 3S, 4R)-1-chloro-3-bromo-4-isopropylcyclohexane
(D) (1R, 2S, 4R)-2-bromo-4-chloro-1-isopropylcyclohexane
(E) (1S, 2S, 4R)-2-bromo-4-chloro-1-isopropylcyclohexane
7. The molecular formulas and 13C NMR chemical shifts (in ppm) are given below.
The splitting pattern of each signal, taken from the non-decoupled spectrum is
given in parentheses. What is the structure?
C4H6O: 18.2 (q), 134.9 (d), 153.7 (d), 193.4 (d)
O
O
(A)
O
(B)
(C)
O
(D)
H
O
(E)
H
8. A bottle was labeled simply "dibromodichlorobenzene" without specifying which
isomer was present. Capillary GC showed that it was a single pure compound,
and the proton decoupled carbon NMR spectrum showed FOUR peaks (not
including solvent). You can conclude that the bottle contained
Cl
Cl
Br
Cl
Br
Br
Br
Br
(A)
Br
Cl
Cl
(B)
Cl
(C)
Cl
Cl
Cl
Cl
Br
Br
(D)
Br
(E)
Br
9. Indicate the expected MAJOR product of the following reaction:
Cl
NaOEt
?
CH 3
CH 3
OEt
CH3
(A)
CH3
(D)
CH3
CH3
(B)
CH3
OEt
CH2
(E)
CH3
CH3
EtO
CH3
(C)
CH3
10. Which of the following molecules have the S configuration?
H
H3C
F
H
Et
H
(CH3)3C
Br
I
D
H
iso-propyl
Br
H3C
II
III
IV
(A) I, II
(B) I, III
(C) III, IV
(D) I, II, IV
(E) all of them
11. Which of the bases below would be best to accomplish the following reaction?
?
CH 2
CH 2
(A) CH3O- Na+
(B) CH3CH2O- Na+
(C) (CH3)2CHO- Na+
(D) (CH3)3CO- Na+
(E) Na+ -OH
CH 2Br
CH 2
CH
CH 2
12. Which compound C9H11Br would give the proton NMR spectrum shown below?
Br
CH2CH2CH3
CH2 CH CH3
(A)
(B)
Br
CH CH2CH3
(C)
(E)
CH2CH2CH3
(D)
CH3
CH CH2Br
Br
Br
13. Which of the following compounds is consistent with the proton NMR spectrum
shown below?
O
O
(A)
O
(B)
(C)
O
O
(D)
(E)
Use the following box to answer questions 14-15
Cl
Cl
Cl
I
and
Cl
Br
Br
II
and
Cl
Cl
III
and
IV
H3C
CH3
H
H3C
H
and
CH3
H
H
Cl
V
and
Cl
Cl
Cl
14. How many pair(s) of enantiomer(s) is (are) there in above five compounds?
(A) 0
(B) 1
(C) 2
(D) 3
(E) 4
15. How many pair(s) is (are) the diastereomer(s)?
(A) 0
(B) 1
(C) 2
(D) 3
(E) 4
Ⅱ. Answer the following team problems: (50pts)
1. Find all chiral molecules of the molecular formula C4H7Cl. (6 pts)
Cl
Cl
Cl
Cl
Cl
Cl
2. (a). Menthyl chloride reacts with sodium ethoxide in ethyl alcohol to give a single
product as shown. Analyze this reaction mechanistically to explain why this is the
only alkene produced. (4 pts)
CH(CH3)2
Cl
CH3CH2O-Na+
CH(CH3)2
CH3CH2OH
CH3
CH3
Menthyl chloride
By contrast, neomenthyl chloride is treated in the same fashion give to a mixture
of products shown below. Moreover, menthyl chloride reacts much more slowly
than neomenthyl chloride. Explain these observations mechanistically. (5 pts)
CH(CH3)2
Cl
CH(CH3)2
CH3CH2O-Na+
CH(CH3)2
+
CH3CH2OH
CH3
Neomenthyl chloride
CH3
CH3
(25%)
(75%)
:Base
H
Cl
Cl
只有一個氫位於trans-coplanar，所以只產生一種alkene
:Base
H
Cl
:Base
H
Cl
有兩個氫位於trans-coplanar，所以會產生兩種alkene。
此外因為後者之產物為三取代雙鍵穩定度大於二取代，所以產率較高。
前者反應速度較慢的原因為六環需經過翻轉後，
產生較不穩定之構型才能有trans-coplanar的氫來進行消去反應，所以反應速度較後者慢。
(b). When menthyl chloride is treated under solvolytic conditions with 80%
aqueous ethyl alcohol, once again, two products are formed in the ratio
shown below. Explain mechanistically. (5 pts)
CH(CH3)2
Cl
CH(CH3)2
CH(CH3)2
H2O
+
CH3CH2OH
CH3
CH3
CH3
Menthyl chloride
(32%)
(68%)
Base
2
1
H
H
1
Cl
H
2
Base
rearrangment
2
H
H
H
H
E1
三級的碳陽離子最穩定所以重排會發生，
所得到的產物亦以三取代的雙鍵最穩定，而產率較高。
3. Chlorocyclohexane reacts with sodium cyanide (NaCN) in ethanol to give
cyanocyclohexane. The rate of formation of cyanocyclohexane increases when a
small amount of sodium iodide is added to the solution. Explain this acceleration
in the rate. (6 pts)
CN
Cl
CN
-
ICN -
I
碘是一個好的離去基亦是好的親合基，
所以可以加速整個反應的進行。
4. 2-Bromo, 2-chloro, and 2-iodo-2-methylbutanes react at different rates with pure
methanol but all produce 2-methoxy-2-methylbutane, 2-methyl-1-butene and
2-methyl-2-butene of same ratio. Explain these results in terms of reaction
mechanism. (6 pts)
x
E1
Nu-
Nu
當X不同時解離的速率也不同，
則整個反狨應速t率也]因此不同。
速率大小為I->Br->Cl-，
此外，因為產物的種類取決於碳陽離子，
三個反應所產生的碳陽離子皆相同，
所以產物的比例亦相同。
5. Consider the following reaction and propose a reasonable mechanism. (6 pts)
CH3CO2H
OAc
Cl
OAc
HOAc
H
Cl
-H +
6. (a) Please propose a reasonable structure for the following spectra. You have to
describle how you obtain your answer. (5 pts)
1
2
3 Br
Br
第一個碳上氫為triplet
第二個碳上氫quintet
第三個碳上氫為triplet
而且第三個碳的位置最為dowm field
(b). The molecular structure and 1H-NMR spectrum (in ppm) is shown below. This
spectrum is measured by Brucker-300MHz machine. The expanded region from
δ 5.0-6.5 in shown at the end of page. Try to analysis it by giving the chemical
shifts for protons, Ha, Hb, and Hc, and calculate the coupling constants. Please
round off figures after decimal point. (7 pts)
"Ha" is
"Hb" is
"Hc" is
"Hd" is
Ha
Hd Hd
Br
Hb
Hc
doublet of triplet.
doublet .
doublet of doublet of triplet.
doublet of doublet.