Knowledge Bank

The microwave spectra of seven isotopic species of 1,1-difluoroethylene ozonide (3,3-difluoro-1,2,4-trioxolane, FCFOOHCHO) have been assigned, including the $parent1$, both $D1$, species, two singly-substituted and the doubly-substituted $\mathrm{<mrow\; data-mjx-texclass="ORD">18</mrow>}O$(peroxy) species, and the $\mathrm{<mrow\; data-mjx-texclass="ORD">18</mrow>}O3$ species. The rotational constants show that, unlike all ozonides previously studied by microwave $spectroscopy2,3,4$, the preferred conformation is an $Op(CH2)$ envelope. The structural analysis is based on a predicate observables method, in which the assumed structural parameters are allowed to vary over a small range to give the best least-squares fit to the experimental data; this tends to reduce the possible effects of a poorly chosen assumed parameter. The results suggest an anomeric interaction to be operative, i.e., a C-F (cis to the envelope flap) bond slightly longer than the C-F (trans to flap) bond with the adjacent C-0 bonds much shorter than the C(H)-0 bonds, and a F(cis)-C-O-O dihedral angle close to $90\circ$. A clear conformational trend of twist: partial Op envelope: full $Op$ envelope is seen in the series of ozonides of ethylene, 1-fluoroethylene, and 1,1-difluoroethylene.