Knowledge Bank

Six isotopic species of cyclobutadiene ozonide (2,3,7-trioxabicyclo(2.2.1) hept-5-ene) containing D. $\mathrm{<mrow\; data-mjx-texclass="ORD">18</mrow>}O$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$ enrichment were prepared by singlet oxygen addition to furan. Rotational and centrifugal distortion constants were determined for all six species and were sufficient to determine the complete structure of the molecule. Perhaps the most interesting structural feature is the non-planarity about the C=C bond, where the hydrogen atoms are bent $8.9\circ$ towards the endo side.