So far, 79 has not been prepared despite many attempts. However, there are var- ious ways of avoiding the interference between the two inner protons. The approach that has been most successful involves bridging the 1 and 6 positions.263 Thus, 1,6- methano[10]annulene (103)264 and its oxygen and nitrogen analogs, 104265 and 105,266 have been prepared and are stable compounds that undergo aromatic sub- stitution and are diatropic.267 For example, the perimeter protons of 103 are found at 6.9–7.3 d, while the bridge protons are at 0.5 d. The crystal structure of 103 shows that the perimeter is nonplanar, but the bond distances are in the range 1.37– 1.42 A ˚ .268 It has therefore been amply demonstrated that a closed loop of 10 elec- trons is an aromatic system, although some molecules that could conceivably have such a system are too distorted from planarity to be aromatic. A small distortion from planarity (as in 103) does not prevent aromaticity, at least in part because the s orbitals so distort themselves as to maximize the favorable (parallel) overlap