RESTRICTED ROTATION IN SUBSTITUTED PROPANE EPOXIDES

Article abstract of DOI:10.1016/S0040-4039(01)81733-0

Dynamic nmr spectroscopy is used to show that 1,1-diaryl-2-methyl-1,2-epoxypropanes display restricted rotation.

Full text of DOI:10.1016/S0040-4039(01)81733-0

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RESTRICTED ROTATION IN SUBSTITUTED PROPANE EPOXIDES
and Rajiv Banavali
Robert W. Murray*
Department of Chemistry
University of Missouri-St. Louis
St. Louis, Missouri 63121
Dynamic nmr spectroscopy is used to show that
Abstract:
display restricted rotation.
Dynamic nmr spectroscopy has been used to study restricted rotation about single bonds in
a
variety of organic compounds.
Of particular relevance to the present studies are the use of
and other olefins3
this nmr technique to study barriers to rotation in substituted
In connection with our studies of carbonyl oxides as monooxygenase enzyme models we have
ozonized
and observed an intramolecular 0
atom transfer from an intermediate carbonyl
Included among the other ozonolysis products
5
The formation of
2 as an
of
was
ozonolysis product is not entirely unexpected inasmuch as sterically hindered olefins are known6
to give epoxides as ozonolysis products in some cases. We present evidence that the barrier to
rotation in
erature.
2 and 3 is high enough to permit observation of the conformer mixture at room
To the best of our
is the first example of this phenomenon in epoxides.
3
3
2
The room temperature nmr spectrum of
indicating high barrier to rotation about the C-C single bond bearing the 1-phenanthryl group.
The diastereotopic methyl groups are seen as arising from conformations of in whichtheremote
part (carbons through 10) of the phenanthrene ring system is cis or trans to the epoxy oxygen.
As the temperature is raised the four singlets in the nmr (270 MHz) spectrum begin to broaden
until one pair coalescence is observed at full coalescence at and finally two
singlets are observed at 167°C. There are six possible ways for the methyl absorptions to be
involved in exchange process. We have used simulated nmr spectra to show that only
2 has four sharp singlets for the methyl protons
a
5
a
a
a
two of these are compatible with the observed variable temperature spectra. The methyl
tions in the extreme conformations are either 1.354 plus 1.240 exchanging with 1.099 plus 1.059