Conical intersections loop construction

The construction of loops relevant to this system was described in Section IVD. In this section, the computational search for the conical intersection using the... 

Figure 6.4 The butadiene cyclobutene ring closure reaction, (a) For the conrotatory reaction, the loop constructed from butadiene, cyclobutene, and bicyclobutane is p (or pi ), and no conical intersection is enclosed, (b) For the disrotatory reaction, the loop is ip (or i ) and encloses a conical intersection.

Figure 6.5 Phase-rule loops for photoreactions of COT. (a) The COT o semibullvalen conversion. All reactions in the loop constructed from the two Kekule forms of COT and semibullvalene are of Htickel type from the number of pairs of electrons that exchange spin, it is seen that the loop is ip and encloses a conical intersection, (b) Loop for the COT tricyclo[3.3.0.0 ]octa-3,7-diene conversion...

Figure 6.7 The 2i7-azirine nitrile ylide conversion. The loop constructed from the azirine and the two isomeric nitrile ylides, which differ by a rotation of the methylene group by 180°, is either ip or i and encloses a conical intersection. The coordinates Qi and Qo are indicated.

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