Orbital correlation diagram cyclobutene, conrotatory ring opening

Figure 7.17 Orbital correlation diagram for conrotatory and disrotatory ring openings of cyclobutenes.

Figure 4.11. Derivation of the orbital correlation diagram for the conrotatory ring opening of cyclobutene a) intended correlation, b) correlation including interaction between a and n and between and o MO s, respectively. Orbiial symmetry labels n and a apply strictly only at the planar cyclobutene and butadiene geometries. Labels S and A, or solid and broken correlation lines respectively, indicate the symmetry behavior with respect to the twofold-symmetry axis (by permission from Michl, 1974b).

Figure 33 shows molecular orbital correlation diagrams for the disrotatory (51) and conrotatory (52) electrocyclic ring opening pathways for cyclobutene. With a total of four... 

The correlation diagrams for the conrotatory process show that there is a good correlation between the bonding orbitals v 1 and v 2 of butadiene and ct- and TT-orbitals of cyclobutene (Fig. 8.40). Thus, the ring opening of cyclobutene to butadiene or the reverse reaction is thermally allowed and occurs by the conrotatory process. The reaction proceeds with conservation of orbital symmetry. The photochemical conrotatory process in this case will be symmetry forbidden. 

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