This month's molecules take us into the realm of fantasy. Helvetane and israelane are two molecules that appear to have been invented by Israeli chemist D. Ginsberg. In a humorous article in Nouveau Journal de Chimie1, he attempts to rationalize a greater stability for israelane as compared to helvetane. It could be that he was motivated more by nationalism than science; israelane resembles the Star of David on the Israeli flag, whereas helvetane resembles the cross on the Swiss flag.
Serious (MNDO) calculations were performed by Li et al. 2 which found helvetane to be more stable by 200 kcal/mol.
The lower energy of helvetane with respect to its isomer can be
understood on the basis of the number of
inward-pointing hydrogens. Helvetane has 4 on each face while israelane has
6. Similarly, the lower symmetry structures for both helvetane and israelane
relieve the steric interactions of inward pointing hydrogens.
Neither of the molecules has been synthesized, nor is there any great effort
in this direction. Therefore one can simply enjoy the pleasing shape of these
two fanciful molecules without concern for politics or sterics.
Note: -prismane, helvetane and israelane share IUPAC name tridecacyclo[12.10.0.02,13.03,12.04,11.05,10.06,9.07,20.08,19.015,24.016,23.017,22.018,21]tetracosane
Mitchell Miller, MDL Information Systems, Inc.