This compound is 1,6-methano(10)annulene, and a classic example of an unusual compound displaying aromaticity.

Aromaticity requires the pi-system to lie in a plane. One might speculate that (10)annulene (shown below) would be aromatic, because it contains a cyclic pi-system of 10 electrons, which appears to be planar. However, because the hydrogens indicated are trying to occupy the same space, the compound is forced out of planarity, and the compound it non-aromatic.

Bianchi and coworkers reported the crystal structure of 1,6-methano(10)annulene. In this compound, the hydrogens that clash in (10)annulene are replaced by a methylene (CH2) group. From directly above, the compound looks basically like naphthalene, with a little extra space in the middle. More interestingly, from the side, it's clear that the atoms of the 10-membered ring are nearly planar, with that methylene bridge oriented perpendicular to the plane.

Reference: Structure of 1,6-methano[10]annulene, R. Bianchi, T. Pilati and M. Simonetta, Acta Cryst. (1980). B36, 3146-3148, https://doi.org/10.1107/S0567740880011089

This compound is 1,6-methano[10]annulene, and a classic example of an unusual compound displaying aromaticity.

Aromaticity requires the pi-system to lie in a plane. One might speculate that [10]annulene (shown below) would be aromatic, because it contains a cyclic pi-system of 10 electrons, which appears to be planar. However, because the hydrogens indicated are trying to occupy the same space, the compound is forced out of planarity, and the compound it non-aromatic.

Bianchi and coworkers reported the crystal structure of 1,6-methano[10]annulene. In this compound, the hydrogens that clash in [10]annulene are replaced by a methylene (CH2) group. From directly above, the compound looks basically like naphthalene, with a little extra space in the middle. More interestingly, from the side, it's clear that the atoms of the 10-membered ring are nearly planar, with that methylene bridge oriented perpendicular to the plane.

Reference: Structure of 1,6-methano[10]annulene, R. Bianchi, T. Pilati and M. Simonetta, Acta Cryst. (1980). B36, 3146-3148, https://doi.org/10.1107/S0567740880011089