Bonding patterns in a strong 3c2e C-H...C hydrogen bond.

Analysis of the topology of the electron density and underlying local orbital interactions of the fully optimized structure of the molecular cage of the in-bicyclo[4.4.4]-1-tetradecyl cation reveals that the inside 3c2e C-H...C hydrogen bond is not only unusual but also strong. The inside C-H bond of the unsaturated, neutral precursor bicyclo[4.4.4]-1-tetradecene is involved in an intramolecular C-H/pi interaction with the transannular double bond. Known and calculated (1)H and (13)C NMR properties, including diamagnetic and paramagnetic contributions to shielding tensors, are accounted for in terms of electron density redistributions and the unusual electronic environment within these hydrocarbon cages.