Page 1156 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

1141
β
H TOPIC 12.1
plane
Computational
α 1
Interpretation of Diene
H H
90. and Polyene
Photochemistry
β
α 1
0.
H
H
90. α 2
H
α 2
90.

Fig. 12.28. Reaction cube locating the butadiene conical intersection in
relation to rotation at each of the bonds. The shaded area in the center
represents the location of the conical intersection with all bond rotations
near 90 . The open circles represent initial excited states. The energy

surface in Figure 12.27 represents the diagonal plane bisecting the cube.
Reproduced from J. Am. Chem. Soc., 115, 3710 (1993), by permission
of the American Chemical Society.

at the MC-SCF/4-31G level of computation. 173a CASPT2 theory, which is appropriate
for excited states with large ionic character, 176 gives a similar description of the CI. 177
Other descriptions of the butadiene excited surface have also been developed, 178 179
including explicit consideration of the formation of bicyclo[1.1.0]butane by 1,3-
bonding. 180
The energy profile in Figure 12.30 compares the disrotatory and conrotatory paths
for cyclization. There is no barrier on the disrotatory path but the conrotatory path

D(1,2,3,4) = 46° D(1,2,3,4) = 119° D(1,2,3,4) = 72°
1
1
1 2.193 2.173
2.033
1.463 1.446
1.451 1.447 98° 1.460 96° 1.479
90° 2 3 4 2
2 3 4 1.447 120° 1.481 3 4
1.433 125°
122°
(a) (b) (c)
Fig. 12.29. Structure of the 1,3-butadiene conical intersections from CAS(6,6)/6-31G* computa-
tions: (a) cisoid, (b) transoid, (c) central. Reproduced from Photochem. Photobiol., 76, 616 (2002),
by permission of Elsevier.

176 C. S. Page and M. Olivucci, J. Comput. Chem., 24, 298 (2003).
177 B. Ostojic and W. Domcke, Chem. Phys., 269, 1 (2001); R. P. Krawczyk, K. Malsch, G. Hohlneicher,
R. C. Gillen, and W. Domcke, Chem. Phys. Lett., 320, 535 (2000).
178
S. Saki, Chem. Phys. Lett., 287, 263 (1998); R. P. Krawczyk, K. Malsch, G. Hohlneicher, R. C. Gillen,
and W. Domcke, Chem. Phys. Lett., 320, 535 (2000).
179 M. Olivucci, I. N. Ragazos, F. Bernardi, and M. A. Robb, J. Am. Chem. Soc., 115, 3710 (1993);
M. Olivucci, F. Bernardi, S. Ottani, and M. A. Robb, J. Am. Chem. Soc., 116, 2034 (1994).
180
S. Sakai, Chem. Phys. Lett., 319, 687 (2000).