Chemistry Reference
In-Depth Information
FIGURE 9.16.
Angular dependence of the EPR signals of
o-6b
when varying the field
orientation from parallel
x
to parallel
y
. The signals marked as “A” can be assigned to off-axis
transitions. The plot also shows the off-axis behavior of transition
z
4, which becomes allowed
when the magnetic field is rotated in the
zy
-plane by a few degrees.
Source
: Reprinted
from Ref. 14 with permission from Wiley.
points parallel to a hypothetical bond angle of 180
of the carbene moiety and thus its
dipolar field is oriented along the
y
-direction of the nitrene contribution. Thus, the
nitrene and carbene contributions are perpendicular to each other and since the
nitrene character prevails over the carbene character, the easy axis of the quartet
D
N bond and the carbene contribution to
the dipolar field points along the
y
-direction, which results in significant magneti-
cally inequivalent
y
- and
x
-directions. The large
E
-value can therefore be interpreted
as resulting from the carbene character of the 1-
4
A
2
ground state.
The lower
E
-value of
o-
-tensor is still oriented parallel to the C
can then be explained from analogous geometric
considerations. Since the carbene center in the aromatic ring is located in the
ortho
position to the nitrene center, the dipolar field of the carbene contribution is not
located perpendicularly to the magnetic
z
-axis of the nitrene center resulting in a
6b
