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Cyclobutadiene Controversy

Some researchers are questioning last summer’s report on the first X-ray crystal structure of the molecule

by Sarah Everts
November 22, 2010 | A version of this story appeared in Volume 88, Issue 47

For years cyclobutadiene has been called the “Mona Lisa of organic chemistry” because the seemingly inscrutable chemical resisted efforts to reveal its crystal structure, despite a deceivingly simple molecular formula. Cyclobutadiene is now also a source of controversy because some researchers are calling into question the first reported X-ray crystal structure of the molecule, which was published in a research paper in Science in July (C&EN, July 19, page 33). Mihail Barboiu and colleagues at the European Institute of Membranes, in Montpellier, France, described how they trapped 4,6-dimethyl-α-pyrone in a guanidinium-sulfonate-calixarene network and then zapped crystals of the complex repeatedly with ultraviolet light to convert the precursor pyrone into CO2 and 1,3-dimethylcyclobutadiene. In separate peer-reviewed technical comments in Science, David Scheschkewitz of Imperial College London and a group of researchers led by Igor V. Alabugin of Florida State University argue that Barboiu and colleagues didn’t make 1,3-dimethylcyclobutadiene but instead crystallized 4,6-dimethyl-β-lactone, an intermediate of the photolysis reaction (DOI: 10.1126/science.1195752; 10.1126/sci ence.1196188). Barboiu and colleagues stand by their initial interpretation of the crystallography data in a response also published in Science (DOI: 10.1126/sci ence.1195846).


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