L. I. U.
Chem. 121, Sect 008, Exam 1
Fall, 2012, 100 points
1. For the following molecules, first make expanded drawings and then name the molecules. (20
pts)
9
(a)
5
7
8
Cl
Cl
OH
4
3
6
2
1
3
8-chloro-7-ethyl-4,4-dimethyl-3-nonanol
(c)
1
(b)
Cl
CH3
2 Br
1 CH2OH
H
2
H
3
CH2CH2CH3
5 6
4
2-bromo-1-chloro-3-isopropylcyclohexane
2
(d) (CH3)3CCH(CH3)CH2CH2CH(CH2CH3)2
CH3
1
6-ethyl-2,2,3-trimethyloctane
1
CH3
2
3
OH
Cl
3-chloro-2-methyl-1-hexanol
CH3CH3
H CH2CH3
C CH CH2CH2 C
3
4 5 6 CH2CH3
CH3
7 8
2. Draw a Newman projection of the low energy conformation of 2,5-dimethylhexane looking
down the C3-C4 bond and for partial credit first make an expanded drawing. (10 pts)
H3C
CH3
HC
CH3
CH3
1
CH
2
CH3
CH2 CH2 CH
4
3
5
CH3
6
H
3
H
H
CH3 H CH3
C
H
H
4
H
H
CH
H3C
CH3
CH3
H
CH
CH3
3. (a) Draw two constitutional isomers of C2H6O. (b) Which isomer has the higher boiling
point? Explain and make a careful drawing to illustrate your answer. (10 pts)
CH3
CH3
O
CH3
much lower b.p.
CH2 O
CH3
CH2 O
H
much higher b.p.
H
hydrogen bond between the
partially positive hydrogen
H
O and the lone pair of the
partially negative oxygen.
CH2CH3
due intermolecular hydrogen-bonding
4. For the following acid-base reactions, identify the acid and the base, give the product of the
reaction, show the movement of the electrons using the arrow formalism, show all charges, and
also calculate the equilibrium constant for the reaction. If the equilibrium constant is very
unfavorable, you can simply state NO REACTION. (25 pts)
O
(a)
C
O H
Cl
pKa 2.92
O
O
+
Na+
C
O C OH
Cl
pKaH 6.2
Keq = 10+3.28
1
O
+
H O
H
Equilibrium is favorable; it lies to the right.
O
O
H
(b)
+
+
-OH
pKa H2O 15.7
pKa 10.1
(c)
Na+
Keq =
+
B Cl
B O
Cl
O
Cl
CH2CH3
Cl
H
10+5.6
Cl H
H
Cl
H O
CH2CH3
5. Which molecule would have the lower heat of combustion, trans-1-isopropyl-3methylcyclohexane or cis-1-isopropyl-3-methylcyclohexane? To answer this question you must
make careful three-dimensional chair drawings of both molecules, showing both conformations
and identifying in each case which conformation would have the lower heat of combustion and
then finally choosing the lowest overall heat of combustion. (15 pts)
1
cis
3
A
B
Conformation A in the cis-isomer is much lower in energy than conformation B, since both
substitutents are in the low energy equatorialj conformation in which theree is no bad 1,3diaxial interaction.
1
trans
3
C
D
Conformation C is lower in energy than conformation D, since the larger isopropyl group is in the less crowded
equatorial position in C.
Overall, the cis-isomer is lower in energy than the trans-isomer since int he cis-isomer both substituents can adopt
an equatorial position. Therefore,the cis--isomer would have the lower heat of combustion.
6. Draw 4 isomers of C5H10. (20 pts). BONUS: Draw 2 more.
2