Christopher M. Hadad
Spring 2001
Chemistry 253
Exam 2
Name (PRINT) ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ
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There are 6 pages and 250 pts on this exam. Please read each question carefully before answering.
1. (20 pts) Each of these compound gives only one signal in its 1H NMR spectrum. Propose a structural formula for each
compound consistent with this information.
(a) C2H 6O
(b) C3H6Cl2
(c) C6H12
(d) C4H6
2. (15 pts) Following are structural formulas for 2 constitutional isomers of molecular formula C6H12O2.
CH3
O
H 3C
O
A
CH3
CH3
O
H 3C
B
CH3
O
H 3C
CH3
(a) Predict the number of signals in the 1H NMR spectrum of each isomer.
(b) Predict the ratio of areas of the signals in each spectrum.
(c) Show how you can distinguish between these isomers on the basis of 1H NMR chemical shifts.
Christopher M. Hadad
Spring 2001
Chemistry 253
3. (15 pts) Below are structural formulas for the cis isomers of 1,2-, 1,3- and 1,4-dimethylcyclohexane and three sets of
13C NMR spectral data (δ, ppm). Match each constitutional isomer to its correct 13C NMR spectral data.
Spectrum 1
Spectrum 2
Spectrum 3
31.35
34.20
44.60
30.67
31.30
35.14
20.85
23.56
32.88
15.97
26.54
23.01
CH3
CH 3
CH3
CH3
CH3
CH3
4. (20 pts) Compound C, which has a molecular formula of C6H14O, readily undergoes acid-catalyzed dehydration
when warmed with phosphoric acid to give compound D (molecular formula C6H12) as the major organic product. The
1H NMR spectrum of compound C shows signals at δ (ppm) 0.90 (t, 6H), 1.12 (s, 3H), 1.38 (s, 1H), and 1.48 (q, 4H). The
13C NMR spectrum of compound C shows signals at δ (ppm) 72.98, 33.72, 25.85, and 8.16 in proton-spin decoupled mode.
What are the structural formulas of compounds C and D?
5. (15 pts) A solution was prepared using 0.0010 g of an unknown steroid (of molecular weight around 255 g/mol) in 100
mL of ethanol. Some of this solution was placed in a 1-cm cell, and the UV spectrum was measured. This solution was
found to have a λmax of 235 nm, with an absolute absorbance (A) of 0.74.
(a) Compute the value of the molar absorptivity (ε) at 235 nm.
(b) Circle which of the following compounds might give rise to this measured UV spectrum with a λmax of 235 nm.
Christopher M. Hadad
Spring 2001
Chemistry 253
6. (20 pts) Draw the most stable pyranose conformation of each of the following sugars.
(a) α-D-arabinose
O
H
C
HO
H
H
OH
H
OH
CH 2OH
(b) β-D-talose
O
H
C
HO
H
HO
H
HO
H
H
OH
CH 2OH
7. (30 pts) Provide the product(s) of the following reactions with D-(Ð)-threose. If there is more than one product,
predict which one will be major.
excess
C 6H 5NHÐNH 2
1) HCN, CNÐ
2) H2O
1) NaBH4
2) H2O
Ac2O
pyridine
O
H
HO
H
H
OH
dilute
warm
HNO 3
CH 2OH
Br2, H2O
Christopher M. Hadad
Spring 2001
Chemistry 253
8. (20 pts) Maltose is a disaccharide that is shown below.
OH
A
O
HO
HO
OH
OH
O
O
HO
OH
OH
(a) What sugar units make up maltose?
B
ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ
(b) What kind of glycosidic linkage is depicted above by the bond marked A?
(c) Is maltose a reducing or non-reducing sugar?
ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ
ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ
(d) What anomer stereochemistry is depicted above by B?
ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ
9. (15 pts) Trehalose, sophorose, and turanose are disaccharides. Trehalose is found in the cocoons of some insects,
sophorose turns up in a few bean varieties, and turanose is an ingredient in low-grade honey made by bees with
indigestion from a diet of pine tree sap. Identify which of the following structures correspond to trehalose, sophorose
and turanose on the basis of the following information. Explain.
(a) Turanose and sophorose are reducing sugars. Trehalose is non-reducing.
(b) On hydrolysis, sophorose and trehalose give 2 molecules each of aldoses. Turanose gives one molecule of an aldose
and one molecule of a ketose.
(c) The two aldoses that constitute sophorose are anomers of each other.
HOH 2C
HOH 2C
HO
HO
HOH 2C
O
O
OH
O
O
HO
HO
HO
HO
HOH 2C
OH
HO
HO
HO
O
OH
O
O
O
HO
CH 2OH
OH
OH
OH
O
OH
OH
CH 2OH
Christopher M. Hadad
Spring 2001
Chemistry 253
10. (25 pts) Provide the product(s) of the following reactions with 1,3-cycloheptadiene. If there is more than one
product, predict which one will be major.
O
O
HÐI
Br2, H2O
O
CH3CH2OH
CN
H 2SO 4
11. (20 pts) Show how a Diels-Alder reaction might be used to synthesize the following compounds in one step from the
appropriate precursors.
O
H
from
(a)
CH3O
H
O
from
(b)
H
O
CO2CH3
(c)
from
CO2CH3
CH3
CN
(d)
from
Christopher M. Hadad
Spring 2001
Chemistry 253
12. (15 pts) Provide a synthesis for the following compound and provide complete reagents and conditions.
O
Start with
HO
C
CO2H
H
H
H
CH 2OH
and prepare
HO
OH
H
CO2H
13. (20 pts) When Br2 is added to 1,3-butadiene at Ð15¡C, the product mixture contains 60% of product A and 40% of
product B. When the same reaction takes place at 60¡C, the product ratio is 10% A and 90% B.
(a) Propose structures for products A and B.
(b) Provide a mechanism to account for the formation of both A and B.
(c) Explain the temperature dependence of the product distribution.