Sheltered deep within the boring hydrocarbon exterior of this cyclophane is an inwardly-directed methine hydrogen forced into the face of a benzene ring. The calculated hydrogen-to-ring distance is only 1.66 Angstroms (ab initio HF/3-21G geometry). Among the unusual spectroscopic consequences are a proton chemical shift of -4.0 ppm and an infrared C-H stretching frequency of 3325 wavenumbers. For a brief communication describing its synthesis and properties, see "Synthesis of in-[3(4,10)][7]Metacyclophane: Projection of an Aliphatic Hydrogen Toward the Center of an Aromatic Ring." R. A. Pascal, Jr., R. B. Grossman, and D. Van Engen, J. Am. Chem. Soc. 1987, 109, 6878-6880.

For those who may doubt the calculated geometry of this compound (there is no X-ray structure), the X-ray crystal structure of a VERY closely related molecule, 2,6,15-trithia-in-[3(4,10)][7]metacyclophane, which is only slightly less strained, is reported in "Small, Strained Cyclophanes with Methine Hydrogens Projected toward the Centers of Aromatic Rings." R. A. Pascal, Jr., C. G. Winans, and D. Van Engen, J. Am. Chem. Soc. 1989, 111, 3007-301.

Theory has at last caught up with experiment, and the in-[3(4,10)][7]metacyclophane appeared on the cover of Chemical & Engineering News (September 28, 1998) in the context of the calculation of NMR chemical shifts!