CHE 230-001 Organic Chemistry Exam 2 (9 total pages including periodic table)
1.
-1-
(6 pts.) Indicate whether each atom indicated is primary, secondary,
tertiary or quaternary. P, S, T, or Q will suffice.
P
T
T
S
Q
P
The Compound below is called nicotine. If you smoke you ‘be free-
2.
basing’ this material? It exists as the free base (as drawn below) in
water at very high pH. When the pH is decrease nicotine becomes
protonated. Nicotine can protonate two times.
N
N
pH > 8
N H
N
5 < pH < 8
N H
N
H
pH < 4
free base
a. (5 pts) Draw the structure of nicotine at pH 8. (see above)
b. (5 pts) Draw the structure of nicotine at pH 4. (see above)
c. (5 pts) Explain your answer, why is one site easier to protonate, Hint:
hybridization and stabilities of acids versus the conjugate bases.
Hybridization stabilizes the lone pair in the pyridine ring (the aromatic
ring). These electrons are in an orbital that is sp2 hybridized and has
more S character than the other lone pair which is in an orbital that is
sp3 hybridized.
CHE 230-001 Organic Chemistry Exam 2 (9 total pages including periodic table)
-2-
3. (9 pts)
Provide IUPAC names for the following compounds. Use E,Z nomenclature when
necessary.
CH 3
O
CH 3
O
(a. 3 pts.)
(b. 2 pts.)
(c. 4 pts.)
a. 4,5-diethyloctane
b. 4-methoxy-5-ethyloctane
c. (Z)-4-methoxy-5-ethyl-4-octene
4. (12 pts.) Compare the acidity of phenol and cyclohexanol. Which one is more
acidic and why?
OH
OH
5a. (6 pts.)
Phenol is more acidic because the anion
(conjugate base) (phenoxide) is resonance
stabilized whereas the conjugate anion of
cyclohexanol is not.
Draw 2,6-dichlorophenol and its conjugate base.
OH
O
Cl
Cl
Cl
Cl
H
H
H
H
H
H
CHE 230-001 Organic Chemistry Exam 2 (9 total pages including periodic table)
5b. (10 pts.)
-3-
Compare the acidity of phenol and 2,6-dichlorophenol.
Which one is more acidic and why?
2,6-dichlorophenol is more acidic due to electron withdrawal of the
chlorine atoms at the ortho positions.
--(-2 wrong but thinking) The lone pairs on the chlorines stabilize the
acid by hydrogen bonding so 2,6-dichlorophenol is more acidic
---(-2 wrong but thinking) The lone pairs on the chlorines destabilize the
conjugate base by resonance so 2,6-dichlorophenol is more acidic.
6. (10 pts.) Calculate the pKa for formic acid given the following.
H2O + HCO2H
H3O(+) + HCO2(-)
The equilibrium constant for the above reaction is K = 9.63 x 10-3. There are 55
moles of water for every liter or the concentration of water in water is 55 molar.
K=[H3O+][HO2-]/([H2O][HCO2H])
Ka=[H3O+][HO2-]/[HCO2H] = K*[H2O] = 9.63 x 10-3 * 55 = 0.53
pKa = -log(Ka) = 0.276
CHE 230-001 Organic Chemistry Exam 2 (9 total pages including periodic table)
-4-
7. Consider the reaction below. (work space for this problem is on the next
page!)
H
H
H
H
H
H
+ NH 2
H
H
H
+
H
NH 3
H
a. (8 pts) What is the equilibrium constant, K of the reaction above
given the following information? pKa of phenylacetylene is 19. the
pka of ammonia is 35.
K = Ka/Ka’ = 10-19/10-35 = 1016 The reaction is favorable as
written!
b. (4 pts) What is the free energy, G of the reaction depicted above
in problem 7? assume (R = 2 cal/mol K) (T = 298 K)
G = -RT Ln(K) = -2*298*Ln(1016) = -22,000 cal/mol = -22
kcal/mol
8. (8 pts) Draw the product of the SUBSTITUTION reaction between the
conjugate base of phenylacetylene (see above) and methyliodide.
a. (2 pts) Name the product above (IUPAC)
Name = 1-propynylbenzene or 1-phenyl-1-propyne
CHE 230-001 Organic Chemistry Exam 2 (9 total pages including periodic table)
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9. (10 pts.) The boat conformation of cyclohexane and the eclipsed conformer
of butane are structurally and energetically similar. Use a couple (short answer)
simple sentences perhaps in combination with Newman projections to explain.
Building a model to solve this problem might help.
Answer:_Bonds in both structures are eclipsed. Both structures
are high in torsional strain. See figure below.
H3C
H
H
H3C
In both New proj.
all bonds are eclipsed!
eclipsed
conformer of
butane
H
H
H2
C H2
C
H
H
H
H
H
H
H
H
Boat Cyclohexane
sight down this
bond!