Orbital correlation diagram cyclobutene, disrotatory ring opening

In this correlation diagram, the orbitals that mix upon disrotatory ring opening have been included in the orbital description of cyclobutene. In fact, little or no interaction exists between this a and n set in the planar cyclobutene. Since mixing between the indicated couples begins with incipient butadiene formation, they have been included for continuity. 

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

Figure 4.7. Disrotatory ring opening of cyclobutene to butadiene a) orbital correlation diagram, b) configuration correlation diagram (dotted lines) and effect of configuration interaction, which converts the diagram into a state correlation diagram (solid lines). The triplet state is indicated by a broken line.

Figure 4.13. Configuration correlation diagram (dotted lines) and the resulting state correlation diagram (solid and broken lines, respectively) for the disrotatory ring opening of cyclobutene, based on natural orbital correlations (by perihission from Bigot, 1980).

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... 

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