Chemistry Reference
In-Depth Information
SCHEME 11.5.
Based on the experimental product and spectroscopic studies on the photo-
chemistry of PFPhN
3
, a mechanism similar to the one for PhN
3
(Scheme 11.5)
has been proposed.
21,22
Platz et al.
21,22
explained that in the case of
1
PFPhN, the ratio of
k
T
/
k
EXP
is
much more favorable for nitrene trapping than with
1
PhN at ambient tempera-
ture. Polyfluorination has decreased the rate constant for ring expansion
k
EXP
and has increased the rate constant for toluene capture
k
T
. Calculations
23a,23b
and experiments
23c
indicate that
1
PhN has an open-shell electronic structure and
it is 18.5 kcal/mol higher in energy than
3
PhN. The diradical (Scheme 11.6)
may undergo very slow stepwise reactions with alkenes to form cyclic azir-
idines, thus it rather undergoes faster BA formation. Platz et al.
21,22
postulated
that fluorine substituents exert an electronic effect making the
p
configuration
more accessible by
-back-bonding. Therefore, fluorine substituents make the
1
FPhN look like a carbene with useful bimolecular chemistry.
12d
This view
received support from the density functional theory calculations by Smith and
Cramer.
23d
p
