Illustrated Glossary of Organic Chemistry
Suprafacial:
A
sigmatropic reaction
or
mechanism
step in which the
sigma bond
changes occur on the same face of the
molecule
.
This suprafacial
1,3-H shift
is thermally forbidden by the
Woodward-Hoffmann rules
. The migrating hydrogen atom (shown in red) started on the top face of the
molecule
, and is on the same face in the
product
.
This
antarafacial
1,3-H shift
is thermally allowed by the
Woodward-Hoffmann rules
, but prevented by excessive
strain
in the
transition state
. The migrating hydrogen atom (shown in red) started on the top face of the
molecule
and is on the bottom face in the
product
.
Related terms:
R group
,
1,2-shift
,
1,2 H-shift
,
1,5 H-shift
,
3,3-shift
,
pericyclic reaction
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