Lower rim through the annulus pathway

The means by which the cone conformer (u,u,u,u) of a calix[4]arene is transformed to its inverted cone conformer (d,d,d,d) remains somewhat uncertain, although it clearly involves a lower rim through the annulus pathway (see Section 4.5.1), One possibility is that the process is concerted (a continuous chain pathway ) without intermediates and only one transition state. Another possibility is that the process is stepwise (a broken chain pathway ) with intermediates and two or more transition states, e.g. cone partial cone - 1,2- or... 

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