610B, Chem. Fall 2001, Prof. Krische Midterm Exam III Name:
Problem 1. (15 points) 2. (30 points) 3. (10 points) 4. (8 points) 5. (15 points) 6. (10 points) 7. (12 points)
Total Points:
/100
1. (15 points) For each of the following pairs, circle the species that embodies the indicated property. A. Faster rate of nitration with HNO3/H2SO4.
CH3
CF3
B. Greater basicity of nitrogen lone pair.
"NB"
N N H "NA" "NA" or "NB"
C. Aromatic stabilization.
D. Greater acidity.
H
H
H
H
O
E. Faster rate of reaction with NaOCH3.
NO2
Cl
NO2
Cl
2. (24 points) Provide the necessary reagents to accomplish the following two-step syntheses.
Br
1) HN O3, H2SO4 2) B r2, FeB r3
O2 N O
1) 2)
O
Br
, A lBr3
H3C CH3
, A lCl3
Cl CH3 Br
1) Br2, FeBr3 2) HNO3, H2SO4
O2N
O
1) AlCl3, Cl 2) H2NNH2, KOH, (or Clemmenson Reduction) 1)
Br O OH
CH3
,AlBr3
2) H2CrO4
1) F eB r3, Br2 2) KOH, 300 C, then HCl
o
OH
2. (continued)
CH3
1) HNO3, H2SO4 2) Fe, HCl, EtOH, H2O then NaOH, H2O 1) NBS, (PhCO2)2 2) NaOMe
H2N
CH3
O
CH3
O
1) H2CrO4 2) HNO3, H2SO4
O2N
OH
OH
1) Mg, ether 2)
Br H O
, then H2O
CH3 OCH3
1) HNO3, H2SO4 2) NaOMe
O2N
O
1) Mg, ether 2) CO2, then HCl
OH
2. (continued)
OH
1) KOH, 300oC, then HCl 2) KOH, CO2, H2O, then HCl
OCH3 OCH3
CO2H
Cl
1)
Cl , AlCl3
2) Cl2, FeCl3
O OCH3 Cl Br
1) AlCl3, 2) Br2, FeBr3
O
3. (10 points) Explain the following observations using resonance structures when appropriate. A. The indicated molecule has an exceptionally large (6.20) dipole moment.
Ph Ph Ph Ph Ph Ph Ph Ph Ph
etc.
Ph
Ph
Ph
Ph
Ph
Aromatic
Ph
Aromatic
Ph
Ph
Ph
Polarization of the alkene that connects the cyclopentadienyl cyclopropenyl subunits in the manner indicated confers aromaticity into the subunits and, hence, is driven by the resonance energy stabilization.
B. In electrophilic aromatic substitution reactions, halide substituents serve as ortho/para-directors, yet deactivate the aromatic ring toward substitution.
Br
Br
Br
Br
E
E
E
E
Br
E
Br
Br
Br
Br
E
E
E
E
Br
E
Halogens effect the system via -inductive and -donation effects. When aromatic ring is attacked by an electrophile attack can stabilize the resulting cation via -donation. However, halogens are very electronegative, and -inductive effects the diminish reactivity of halo-arenes.
4. (8 points) Like carbon, nitrogen may be SP, SP2 or SP3 hybridized. For each compound, indicate the hybridization state of nitrogen.
CH3 N H3C H3C N CH3 H O N CH3
sp
2
CH3
H3C
C
N
sp
3
sp
2
sp
NH2
O
N
O
O
N
O
N
CH3
sp
sp2
sp2
sp2
5. (15 points) Provide mechanisms to account for the following transformations. Draw all relevant resonance structures. A. Nucleophilic Aromatic Substitution
O N O Na O CH3 H3C O N O
F
O
O N O F F H3CO
O N O F H3CO
O N O F H3CO
O N O
O
CH3 O N O
H3CO
B. Acid promoted cleavage of phenolic ethers.
O CH3 H Br H3C Br OH
H O CH3 H Br O CH3 Br OH
+ CH3Br
NOT
H O CH3 Br
Br
C. tert-Butyl groups can be cleaved upon exposure to acid. This reaction is simply the reverse of an electrophilic aromatic substitution reaction. Provide a mechanism for this transformation. Hint: first sketch the mechanism of the reverse reaction on the back of this page.
H O O S O O H
H H O OSO H O
O OSO H O
H
H
H
O OSO OH H
H
O OSO H O
6. (10 points) Bromobenzene was exposed to magnesium filings and the resulting Grignard reagent was reacted with an unknown aldehyde. The resulting product was exposed to an oxidant, MnO2, to provide a compound with the spectral characteristics indicated below. What are the structures of the two products? For the final product, mass spec reveals a molecular form...