Chemistry Reference
In-Depth Information
107º
126º
142º
1.10º
+
1.91
1.10
90º
36.4
1.87
2.36
32.0
36.7
1.96
27.1
31.6
TS2
28.6
TS3
TS4
18.0
14.5
8.6
+
8.9
TS1
1
49b
1.4
0.0
1.5
0.0
122º
112º
126º
107º
1.13
1.25
2.30
1.25
1.13
anti-48b
syn-48b
2.22
-11.4
-11.4
-9.9
-9.9
+
+
50b
50b
FIGURE 12.17.
The free energy surface (
DG
(298 K), kcal/mol) for stepwise and concerted
Curtius rearrangement of methoxycarbonyl azide (
48b
,CH
3
O-CON
3
) at the B3LYP/6-311
þ
G(
d
,
p
)//B3LYP/6-31G(
d
) (red, top) and CBS-QB3 (black, bottom) levels of theory.
18
Dis-
tances are shown in A
, and angles are in degrees.
Source
: Reprinted with permission from Ref. 18.
Copyright 2004 ACS Publications.
initially, and subsequently relaxes to a less selective,
lower energy triplet
intermediate.
124
Insertion of
1
49a
into the CH bond of alkanes and the OH bond of alcohols,
addition of
1
49a
to acetylenes, and its reaction with benzene, followed by azepine
formation, are all well documented.
6
Similar results, namely, formation of nitrene-derived products and the absence of
isocyanate products, were obtained upon photolysis of (4-acetylphenoxy)carbonyl
azide.
51,52
To understand the difference in the reactivity of carbonyl azides (R-CON
3
,
aryl, alkyl), Liu and coworkers
18
investigated stationary points on the PES for the thermal decomposition of both the
acetyl azide (
R
¼
aryl, alkyl) and azidoformates (RO-CON
3
,R
¼
1d
, Fig. 12.1) and the carbomethoxy azide (
48b
, Fig. 12.17).
Similar to
1d
, two stable conformations were localized for azidoformate
48b
.As
for
, the less stable form positions the azide group
anti
to carbonyl group
(Fig. 12.17).
18
In the gas phase, the difference between the free energies of two
conformers is predicted to be 4.5 and 1.5 kcal/mol for
1d
, respectively (at the
CBS-QB3 level). The activation free energy for the conversion of the
syn
conformer
to the
anti
one was found to be 10.8 and 8.9 kcal/mol for
1d
and
48b
1d
and
48b
, respectively
