  In this communication a systematic computational survey on some rigid
hydrocarbon skeletons, e.g. half-cage pentacyclododecanes and
tetracyclododecanes, and their chlorinated derivatives in order to seek for the
so-called ultrashort "non-bonded" hydrogen-hydrogen contacts is done. It is
demonstrated that upon a proper choice and modifications of the main
hydrocarbon backbones, and addition of some chlorine atoms instead of the
original hydrogen atoms in parts of the employed hydrocarbons, the resulting
strain triggers structural changes yielding ultrashort hydrogen-hydrogen
contacts with inter-nuclear distances as small as 1.38 Angstrom. Such
ultrashort contacts are clearly less than the world record of an ultrashort
non-bonded hydrogen-hydrogen contact, 1.56 Angstrom, very recently realized
experimentally by Pascal and coworkers in in,in-bis(hydrosilane) [J. Am. Chem.
Soc. 135, 13235 (2013)]. The resulting computed structures as well as the
developed methodology for structure design open the door for constructing a
proper set of molecules for future studies on the nature of the so-called
non-bonded hydrogen-hydrogen interactions that is now an active and
controversial area of research.
