2006 Fluorocarbons Final (250 pts doubled is 500)
NAME:
1) Easy Questions (90pts)
a) (16pts)
Where does the name fluorine come from?
What is a fluorocarbon?
What is the name of the only known enzyme to create a C-F bond?
Name a fluorinated product you encountered this week.
Give two similarities between Hydrogen and Fluorine.
What are the three characteristics that make fluorine such a special and unique
substituent?
Name four famous fluorine chemists mentioned this semester (Dr. Roche is not famous!)
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b) (22pts)
Draw a Lewis structure with lone pairs for a:
fluorine atom
fluorine molecule
fluoride ion
hydrogen fluoride
State and briefly explain one historical reason why organofluorine chemistry grew
rapidly during the 1900’s.
Give one possible reason why nature finds it (almost) impossible to synthesize
organofluorine compounds?
Circle which bond is longer
C-H
or
C-F
Circle which bond is more polar
C-H
or
C-F
Circle the molecule with the stronger σ bond:
CF4
CF2H2
BBr3
BCl3
F-F
Cl-Cl
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c) (12pts)
Match the reagents with the correct process:
KF, Sulpholane
Nucleophilic Trifluoromethylation
(CH3OCH2CH2)2NSF3
Electrophilic Trifluoromethylation
CsF, Diglyme
Oxidative Fluorination
Nucleophilic Epoxidation
CoF3
Cartman Chiral Fluoridation
t
BuOOH, tBuLi
Electrophilic Epoxidation
F2
Nucleophilic Fluorination
O
F3C
Migratory Insertion
O
O
CF3
O
, heat
Poptart Epoxidation
Reductive Defluorination
Garrison Cycloaddition
N
TfO +
F
-
CF3-TMS, TBAF
Electrophilic Fluorination
Fellonthefloorification
Oxidative Elimination
Pb(OAc)4, HF
Radical Fluorination
SF4, HF
Radical Trifluoromethylation
F2, HCO2H
DeoxoFluorination
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d) (20pts) These ten questions are True/False:
Selectfluor™ is more reactive and dangerous than elemental Fluorine.
BAST and DAST reagents are safer alternatives to SF4.
Perfluorocarbons and analogous hydrocarbons have similar boiling points.
Hexafluorobenzene will undergo Nucleophilic Aromatic Substitution reactions.
Perfluoroalkyl-alkynes are more stable than fluoro-alkynes.
Perfluorocarbons are normally more dense than hydrocarbons.
Perfluorocarbons will undergo reductive defluorination reactions with strong electron
donors.
Fluoride ion is a worse nucleophile in methanol than chloroform.
Tetrafluoroethene undergoes thermal concerted [2+2] cycloadditions.
19
F is more naturally abundant than 18F.
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e) (20 pts)
Circle the weakest sigma bond in each molecule:
H
F C H
F
H
HH
F
H
F
H
H
H
F
H
H
H
H
H
H
Circle the more stable situation in the following pairs:
a)
b)
F
H
F
F
F
c)
d)
e)
F
H
F
Cl
F
H
F
Rank the following aromatics in increasing reactivity towards nucleophilic aromatic
substitution reactions.
CH3
NO2
F
F
OH
F
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F
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2) Transformations (4x15 = 60pts) Fill in the products:
NaOCl
F3C
CF3
F3C
F
CH3ONa
O
O
SF4 / HF
H
DAST, hexane
Heat
HO2C
1) KOH
2)CF3-Si(CH3)3, CsF, THF
3) H2O
CO2H
F2/N2
CoF3
HCO2H
SelectFluor
CH3CN
H-Br
Peroxides
F2C CFH
(two products)
CF2=CCl2
Heat
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3) Detailed Questions (3x20 = 60pts)
Answer three of the four following questions:
a) Explain why PFIB is more reactive than HFP is more reactive than TFE towards
nucleophiles.
less reactivemore reactive
CF2=CF2
<
CF2=CFCF3 <
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CF2=C(CF3)2
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b) In this DAST reaction, explain why the three different solvents encourage the three
different products.
OH
hexane
F
N S F
CH3CH2
F
CH3CH2
CH2Cl2
THF
F
F
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c) Explain the formation, and the relative ratios, of the three products generated in the
following reaction.
CF2
CF2
80oC
F2C CF2
F2C CF2
(82%)
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(14%)
CF2
CF2
(4%)
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d) Why did the Montreal Protocol seek to put a ban on the production and use of
chlorofluorocarbons?
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4) Mechanisms (2x20 = 40pts)
Using curly arrows, write mechanisms for two of the three following reactions.
a)
CCl3
HF, SbF5
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CF3
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b)
Cl
Cl Cl
Cl
Cl
Cl
KF, N.M.P.
180oC
Cl Cl
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F
F F
F
F
F
F F
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c)
Ph
Ph
F2, H2SO4
CH3CN, H2O, reflux
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O
Ph C CF2-Ph
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