Chemistry Reference
In-Depth Information
CH
3
NCO
2d
O
2255 cm
-1
-
N
CH
3
> 2 × 10
7
s
-1
S
+
h
v
266 nm
??
1
45a*
3
45a*
45a
> 2 ×10
7
s
-1
1
3
O
O
Adduct
1776 cm
-1
45a
or
44
H
3
C
N
N
3
3d
H
3
C
1
3d
1518 cm
-1
1780 cm
-1
CH
3
CN
O
1648 cm
-1
H
3
C
N
N
CCH
3
46a
-
+
SCHEME 12.20.
Proposed photochemical processes for
45a
based on the TRIR data.
26
forming the TRIR signal attributed to
3
3d
, it was estimated that the triplet state is no
more than about 1 kcal/mol above the singlet ground state.
26
Thus, experimentally
derived
E
ST
is noticeably smaller than the gas phase value calculated at the CBS-
QB3 and G2 levels,
18
although the difference is not substantial.
The photochemistry of
N
-trifluoroacetyl dibenzothiophene sulfilimines (
D
,
Scheme 12.19) was also studied using TRIR spectroscopy and product studies.
26
Unfortunately, the results of TRIR study are too complicated.
26
It is not surprising, as
the characteristic IR band of the singlet trifluoroacetyl nitrene (
1
47
45b
) at about
1770 cm
1
has very low intensity (Fig. 12.16a). Moreover, the characteristic triplet
carbonyl nitrene band at about 1500 cm
1
(Fig. 12.16b) has much less intensity than
those of
1
3a
and
1
3d
. For all triplet nitrenes, the C
O stretch contributes mainly to
the latter characteristic vibration.
In turn, the product studies demonstrated that photolysis of
in the presence of
cis
-or
trans
-alkene (4-octene) leads to aziridines with incomplete retention of alkene
stereochemistry.
26
The different
trans
/
cis
ratios from
cis
- and
trans
-4-octene were
observed (2.4 and 3.5, respectively, at 0.89M of alkene) and attributed to the fact that
both singlet and triplet nitrenes react with the alkenes.
26
The
trans
/
cis
ratios change
only slightly on reducing the alkene concentration (2.3 and 3.1 at 0.012M of alkene).
The observation of the trifluoroacetamide as a major product of the
45b
45b
photolysis in
i-PrOH indicates that triplet reactivity is significant.
The singlet-triplet splitting for the acetyl nitrene (
3d
) and its trifluorosubstituted
analogue (
47
) have been calculated using a set of computational methods (B3LYP/6-
