Pyramidalization of the sp2-Hybridized Carbon Atoms in 1,4-Bridged 2,5-Cyclohexadienes

The 2,5‐cyclohexadiene‐2,3‐dicarbonitrile derivatives 1–7, the 1,4‐positions of which are linked by bridges with increasing lengths, have been prepared in order to determine the influence of the bridging on the structural parameters of this system. Therefore, we have examined the molecular structures of 1–7 by X‐ray analyses. Depending on the length of the bridge, the endo pyramidalization of the sp2‐hybridized carbon atoms established for 1 and 2 changes into exo orientation in the derivatives 5–7 to prevent eclipsed conformations between the substituents on the double bonds and on the bridgehead atoms. The intramolecular distances and folding angles of 2–7 vary systematically with the length of the bridges except the distance between the double bonds which is fixed to a magnitude of 2.42–2.45 Å. The syntheses of the compounds 1, 4, and 7 have not yet been reported in the literature.