Adapted from PLTL
Names: ___________________
Chem 227/ Dr. Rusay
Aromaticity
1.
Predict whether each of the following systems is aromatic, anti-aromatic (an
estimate), or non-aromatic. Assume that each system is planar, and justify your
choice. Predict a specific chemical and/or physical property that would allow a
conclusive determination of the aromatic, anti-aromatic or non-aromatic character
of the compound.
O
NH
O
A
B
C
N
N
N
E
A
B
C
D
E
F
G
H
F
D
N
H
G
H
2.
Provide reasonable explanations for the following observations:
a.
Neither of the following [10] annulenes shows any special
stability. (Viewing a model is recommended.)
b.
The following [18] annulene gives 1H NMR signals at δ 3.0 ppm
and δ 9.3 ppm.
H
H
H
H
H
H
c.
The compound below reacts with HCl to give a weak acid (pKa ~
5-6). What is the structure of that weak acid?
N
N
H
d.
Cyclopropenium ion is quite stable, but cyclopropene is not.
Diphenylcyclopropenone has a dipole moment equal to 5.08 D, whereas
benzophenone (diphenyl ketone) has a dipole moment equal to 2.97 D.
O
cyclopropenone
cyclopropene
cyclopropenium
ion
e.
The following synthetic procedure failed; the starting material was
recovered unreacted.
H
I
H
CH3 OH solvent
OCH3
+ HI
Δ
f.
1,3-Cyclopentadiene is extremely acidic for a hydrocarbon (pKa
15) whereas 1,3,5-cycloheptatriene is extremely nonacidic (pKa much too
high to measure).
H
H
H
H
3.
Compound A, when treated with aqueous sulfuric acid, was converted to isomeric
compound B (C9H12). When B was heated for an extended time with chromic
acid, dicarboxylic acid C was obtained. a) Give the structure of B. b) provide a
mechanism that accounts for the formation of B from A. c) Explain what UV
spectrocopy data would distinguish B from A. d) Explain what IR spectrocopy
data would distinguish C from B. e) Explain what 1H NMR and 13C NMR
spectrocopy data would respectively distinguish B from C.
CO2H
H2SO 4
K 2CrO7
H2SO 4, H2O
B (C9H12)
H2O
Δ
A
a)
b)
c)
d)
e) 1H
13
C
CO2H
C