Over the 25 years Robert Liu [from the University of Hawaii!] has emphasized that the
"hula twist" is ubiquitious in photoisomerisation reactions [where after a molecule absorbs a photon it undergoes a structural change] and is beautifully summarised in the figure below.
This short review by Liu and Hammond [whose address is Aloha, Oregon!] documents this and also argues that the hula twist is driven by steric considerations because it is "volume conserving".
However, it turns out that this geometrical change can be preferred purely by an electronic mechanism and does not require steric hindrance. Seth Olsen and I show this [amongst many other results, some of which I have discussed in a previous post] in a paper just published in Journal of Chemical Physics.
We refer to the "hula twist" as disrotatory motion and discuss it briefly on page 12 of our paper.
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