1. Friedel-Crafts Revisited Oxidizing/Reducing Scheme
Chemistry 125: Lecture 67 April 11, Triphenylmethyl Spectra
Friedel-Crafts Revisited Oxidizing/Reducing Scheme
Alcohol Oxidation Mechanism
This
For copyright notice see final page of this file

3. Triphenylmethyl Dimer
CPh3
Triphenylmethyl Dimer
60 MHz PMR Spectrum
in CS2
a,a-coupling
a,para-coupling
J = 3 Hz J
10 Hz
25 H
2 H
1 H

4. Triphenylmethyl Dimer
60 MHz PMR Spectrum
in CS2
a,a-coupling
a,para-coupling
300
400
500
l (nm)
Absorbance
-60°C
318 nm
non-bonding SOMO
+21°C
513 nm
ultraviolet

5. Correct dimer dropped for 46 years, because they thought
Journal of the American Chemical Society – Next Year
Correct dimer dropped for 46 years, because they thought
it should be colored!

6. Third Thoughts on
Friedel-Crafts
This

7. Rearrangement in Friedel-Crafts Alkylation
Lee and Woodcock (1970)
Where?
<2% D2 elsewhere
3/7
2/7
< 2% partial or full methide shift en route to n-propyl benzene
Deno (1968) D+ D
90% +
with one D
forms via benzene nucleophile SN2
AlCl3 + Cl
5°C, 45 min D H +
gives i-PrPh product (SN1) H
What if CH3 gets stuck halfway?
CH3
Which of these gives
the n-PrPh product in Friedel- Crafts?
gives
n-PrPh product
(SN2)
Still + +
Ipatieff 1940 J Org Chem conversion of benzene calc. assuming ethyl second subst is 12x faster than first +
gives
n-PrPh product!
Still
gives
n-PrPh product
(SN2?)
CH3 Cl
AlCl3 Cl
AlCl3 + Nu
Protonated Cyclopropane
(stability between
1° and 2° cations)
PROBLEM:
How to decide?
why not
Methide Shift?
Hydride Shift

8. Oxidation/Reduction as Bookkeeping
(for purposes of reagent selection)
Need a “reducing agent”
(CH3)3C C CH3 O
(CH3)3C C CH3 OH H ? C C
“reduction” +2 +1 -2
H2O
Oxidizing:
Reducing:
Neither:
H-Cl
KCl
Br-Br
RS-SR
CrO3
CH4
LiAlH4
NaH K
RSH
Not all reducing agents would work satisfactorily, but it is typically futile
to try a reagent from
the wrong redox class. H OH -2 -3 -1
But photosynthesis
changes H2O into O2
and “H-” (NAD+  NADH)
H2C CH2
H2O

9. Carbon “Oxidation States” (Prof. Siegel, Lecture 47, 2010)
This scheme from 2010 is better organized that this year’s which follows.
0:49-11:35

10. Carbon “Oxidation States”
2011

11. Alcohol Oxidation (e.g. J&F Sec. 16.14)
2010
Br2 Mechanism

12. Alcohol Oxidation (e.g. J&F Sec. 16.14)
2011
Br2 Mechanism

13. Alcohol Oxidation (e.g. J&F Sec. 16.14)
2010
Cr+6 Mechanism

14. Alcohol Oxidation (e.g. J&F Sec. 16.14)
2011
Cr+6 Mechanism

15. Pyridinium Chlorochromate (PCC)
Stopping at Aldehyde
(e.g. J&F pp )
-O-Cr-Cl O +
+ CrO3 + HCl
Pyridinium Chlorochromate (PCC)
n-C9H19-CH2OH
n-C9H19-CH=O
(92% yield)
PCC
CH2Cl2
no water; no gem-diol;
no overoxidation
(Loudon)
“In practice the chromium byproduct deposits with pyridine as a sticky black tar, which can complicate matters.” (Wikipedia)

16. End of Lecture 67 April 11, 2011
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