Download Sample Exam #2 Answer Key

1
CHEM 10052
Spring 1998
Exam #2
Name_____________________
ss#_______________________
1) Compare the molecular structure and physical properties of alcohols and thiols.
Include descriptions of geometry, orbital hybridization, hydrogen bonding, relative
melting points and boiling points, and water solubility. (10 pts.)
O
S
R
H
R
H
alcohols
thiols
Alcohols and thiols have a bent geometry with 109.5º bond angles and are sp3
hybridized.
Alcohols are very polar compared to thiols due to the greater
electronegativity of the oxygen in these molecules. Alcohols also exhibit good hydrogen
bonding properties while thiols are incapable of hydrogen bonding. Consequently,
alcohols have comparatively higher melting points, boiling points and densities than
thiols. Finally, alcohols are much more water soluble than thiols due to their greater
polarity and hydrogen bonding.
2) Compare the molecular structure and physical properties of aldehydes and ketones.
Include descriptions of geometry, orbital hybridization, hydrogen bonding, relative
melting points and boiling points, and water solubility. (10 pts.)
O
O
C
C
R
H
R
R
aldehydes
ketones
Both aldehydes and ketones are trigonal planar with 120º bond angles and sp2
hybridization. Aldehydes are slightly more polar than ketones and both are more polar
than alcohols. While hydrogen bonding is not possible between aldehyde or ketone
molecules, both are capable of hydrogen bonding in solvents such as alcohols or water.
Aldehydes may have slightly higher melting points, boiling points and densities as
compared to ketones. Simple aldehydes and ketones are water soluble.
3)
Name the following compounds using either common nomenclature or IUPAC
systematic nomenclature (2 pts each).
O
O
C
CH3 CH2 CH2 CH
CH3
a)
3-methylcyclohexanone
NO2
b)
2-nitropentanal
O
SH
H
CH CH2CH3
c) CH3
2-butane thiol
SH
H
SH
d)
2-mercaptobenzaldehyde
OH
e)
cis-2-mercaptocyclopentanol
2
4) Draw structural formulas for the following compounds (2 pts. each):
a) 2-mercapto-1-butanol
OH
H2C
b) 2,2-dimethoxypropane
OCH3
H
C CH2CH3
H3C
CH3
SH
c) 3-pentanone
d) 2-heptanol
OH
O
CH3CH2
C OCH3
CH3CH2CH2CH2CH2
C CH2CH3
C CH3
H
e) 3-hydroxy-2-methylhexanal
OH
CH3CH2CH2
O
C CH C H
H
CH3
5) Predict the major products for the following reactions (3 pts. ea.)
a) CH3CH2CH2CH2OH
O
[Ox.]
CH3CH2CH2
-
b) CH3CH2OH + Na
C H
CH3CH2CH2
+
OCH3
+ CH 3Br
+ NaBr
OH
O
CH3CH2
1) cat. NaOH
d)
O
CH3CH2O Na + H2
O- Na+
c)
[Ox.]
CH3 CH2 C H
CH3 O
+
2) H2O, H
OCH3
e) CH3 CH2 CH2
C CH C H
H
CH3
O
+
H2O, H
C
CH3
O
CH3CH2CH2
C CH3 + 2 CH3OH
C OH
3
CH3
O
f) CH3 CH CH2 C H
CH3
[red.]
CH3
CH3
H
C C
H
CH3
OH
g)
CH3
C CH2CH3
H
C CH2 CH2OH
H
H2SO4

OCH3
O
OCH3
dry HCl (g)
+ 2 CH 3 OH
h)
S
SH
S
Br 2
+ 2HBr
i)
O
O
j.) CH3CH2
C OCH3
CH3CH2
NaOCH3
O
C CH C OCH3
CH3
6) Write a detailed mechanism for the aldol condensation reaction of ethanal (10 pts.).
O
cat. NaOH
C
CH3
H

O
H2O
HO

CH3
C H
H O
H C C H
H
H
O
O
CH3
C H
H C C H
H
H
H
OH
CH3
C H
O
O
O
H C C H
OH
H C C H
H
7) Write a detailed mechanism for formation of acetals starting with acetone (10 pts.).
O
CH3 C CH3 + 2 CH 3OH
+
H
See notes
4
8) The following compound can be made by a mixed aldol reaction between two
different carbonyl compounds. What two starting materials would you use? (4 pts)
OH
A + B
cat. NaOH(aq)
CHCH2 C CH3
O
C
O
O
H + CH C CH
3
3
A
B
9) The amino acid cysteine forms a disulfide when oxidized. What is the structure of
this disulfide? (3 pts)
O
HSCH2 CH C OH
NH2
O
O
H
H
HO C C CH2 S S CH2 C C OH
NH2
NH2