The extent of a push-pull mechanism in this type of reaction causes the rotation-inversion controversy. A kinked methyl group allows this reaction to occur through one bond flip and a triplet biradical (“bi-radical”) at a conical intersection. This type of reaction alternates with helix inversions on a crowded rotaxane (“ro-TAX-ane”) to power Ben Feringa’s first unidirectional molecular motor. This reaction turns the square planar compound bistriphenylphosphine platinum chloride yellow. The large change in molecular volume required for this reaction is accommodated by a hula twist. Azobenzene and stilbene act as molecular switches because they undergo this reaction under UV light. When a conjugated aldehyde undergoes this reaction, an opsin is triggered in the retina. This reaction temporarily breaks a stiff pi bond, allowing its substituents to rotate 180 degrees. For 10 points, name this reaction that interconverts alkene isomers. ■END■
ANSWER: cis–trans isomerization [or cis–trans interconversion; or E–Z isomerization or E–Z interconversion; or geometrical isomerization or conversion between geometrical isomers; accept descriptions of switching between cis and trans or E and Z alkenes; prompt on double bond isomerization or alkene isomerization or olefin isomerization; prompt on isomerization or photoisomerization by asking “what is the chemical outcome of the isomerization?”; reject “rearrangement”]
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