Chem 232. D. J. Wardrop
. Problem Set 7. Question 1. c. Rank
each carbocation in order of increasing stability (1 = least stable; 4 = most ...
D. J. Wardrop
Chem 232
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Problem Set 7 Question 1. c.
Rank each carbocation in order of increasing stability (1 = least stable; 4 = most stable)
e.
Rank in order of increasing heat of hydrogenation (∆Hhydrog) (1 = lowest ∆Hhydrog, least exothermic; 5 = highest (∆Hhydrog, most exothermic).
Question 2. Toluene (1) undergoes benzylic bromination when heated with N-bromosuccinimide (NBS, 2). Before toluene (1) reacts though, NBS (2) generates both bromine radicals (Br•) and diatomic bromine (Br2). First, draw the product of this reaction. Second, draw the mechanism for the homolysis of NBS to provide a bromine radical. Third, draw a mechanism involving a termination step that shows how Br2 is formed in the reaction. Finally, draw the mechanism for the radical bromination of toluene (1) using the bromine radical and Br2 generated from NBS (2).
O CH3 +
1
N Br O 2
heat
Question 3. Draw the major organic product in the boxes provided for each reaction scheme below. If the reaction is regioselective, only draw the major product. Be sure to indicate the correct relative stereochemistry (i.e. dashes & wedges or axial & equatorial bonds) where appropriate.
O O
1,3-pentadiene heat
KOt-Bu Br
THF
O
single isomer
single isomer
CH3 1. C2H2 (acetylene) heat
HBr 25 °C (thermodynamic control)
2. Pd/C, H2
CH3
single isomer
O heat
HBr
N Br CHCl3
-80 °C (kinectic control)
O
O
O
OH Zn(Hg) H
heat
O
Br2 (no light)
HCl
NBS, CHCl3
1,4-addition
heat
O Me heat O
O
Me Me
NBS, BzOOBz heat
single isomer
Question 4. Write the name for the principle functional group present in each molecule (e.g. ketone, alcohol, amine, etc.). If there appears to be more than one functional group present, name them singularly (e.g. vicinal chlorhydrin rather than alkyl chloride and alcohol). Do not write the IUPAC name or common name for the molecule, just the functional group name. O H3C
CH3
H3C
OH
H3 C
CH3
O Br
H3 C
Cl
O
OH H3C
Br
O
O
O O
H3C
CH3
OH
NH2
H3C
O
CH3
H3 C
O H3 C
O
CH3
OTs H
OH CH3SCH3
H3 C
H N
H3 C
CH2
O CH3
H3 C C N
H3 C
OH
O
Question 5. For each of the molecules shown below, use electron-counting and Huckel's rule to determine whether they are aromatic, anti-aromatic or neither. Note that where heteroatoms are shown with a lone pair, this atom contributes two electrons to the pi-bonding system.
H
Me
H
H
N H
Me H
H H
H
H
Br
H H
2-
H
H H
H
try drawing some resonance structures! H
H
Me
Me
Question 6. Using the Frost Circle mnemonic, draw the molecular orbital diagram for a cyclopentadienyl carbanion (energy levels only). Indicate which MOs are bonding, non-bonding and antibonding. Use up and down arrows to represent the electrons present in each orbital. State whether a cyclopentadienyl carbanion is aromatic, antiaromatic or neither. Use your diagram to explain. H H
H H
H
