The symmetry of the Ion formed by stepwise loss of CO molecules in the mass spectra of p-benzoquinones

Contrary to previous suppositions, it appears that the produced by the loss of 2 CO from para‐benzoquinones passes through the symmetry of not a substituted cyclobutadiene, but rather a substituted tetrahedrane, at least for inert R. The p‐fluoro labeling technique is used to obtain this result.