Chemistry Reference
In-Depth Information
CN
N
N
- 49.1 (- 49.7)
N
N
N
N
130
N
N
123
124
TS
2.5
CN
(7.4)
3A" 3.1 (-8.9)
1A" 9.7 (10.9)
N
NH
C
TS
N
N
N
TSH
18.5
26.4
N
NC
N
C
H
128
132
s-E
0.0 (0.0)
s-Z
0.5
129
19.5 (22.4)
s-Z-cis
-16.5
s-Z-trans
-18.8
s-E-cis
N
N
TS
9.9
-21.1
s-E-trans
-17.5
N
TS-1,3H
N
85.9
N
N
N
C
N
H
127
125
3A" 0.4 (-11.0)
1A" 8.2 (12.9)
4.1 (4.8)
NC
131
s-Z-cis
-17.9
s-Z-trans
-15.6
s-E-cis
-17.9
s-E-trans
-17.4
G3(MP2) energy values (CASPT2/6-31G*+ZPE values in parentheses) in kcal/mol.
SCHEME 8.22.
and at 330 nm in the UV. This IR spectrum agrees very well with the calculated
spectrum for nitrile ylide
(unlabelled) at the B3LYP/6-31G
level (1409, 1455,
1537, 2169, and 2279 cm
1
). A weak band also present at 1986 cm
1
may be
assigned to the cyclic carbodiimide
141
.
Photolysis of the azido chloropyrazine
140
at 222 nm afforded a species
absorbing at 638 (strong), 648 (strong), 1011 (medium), 1424 (medium), 1599
(strong), 1968 (strong), and 2190 (very weak) cm
1
in the IR, which is very close to
the calculated spectrum of the nitrile ylide
143T
/
143A
. Aweak band at 1968 cm
1
, possibly
146
at 400
C with deposition of the product
in Ar matrix at 10 K. FVT afforded cyanoimidazole
due to
145
, was also observed on FVTof
143
147
as the main product. As
expected, carbodiimide
148
and cyanamide
149
were not observed due to the higher
barriers for Cl shifts (Scheme 8.24).
It is noted that the cumulene-type stretching vibrations of the cyclic nitrile ylides
appear in a wide range of the infrared spectrum, from about 1935 to 2156 cm
1
.Itis
known that the structures or nitrile ylides and nitrile imines are very variable, with
consequential large shifts of the IR frequencies.
44
