Molecules of the Month - August 1996

The Asteranes:

Helvetane and Israelane

[A ChimeTM-enhanced version* is also available here.]

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.

(Structure of 12 prismane) (Structure of helvetane) (Structure of israelane)
In the course of AM1 studies of ladderanes (polycyclic hydrocarbons composed of anti-fused cyclobutane rings) and prismanes (macrocyclic hydrocarbons that can be conceived as two regular n-gons connected by bonds between all pairs of corresponding vertex carbons), researchers at Queens College of the City University of New York examined helvetane and israelane as structural isomers of [12]-prismane.3 Whereas previous workers2 had assumed D4h symmetry for helvetane and D6h symmetry for israelane, we allowed the structures to relax and found D2d and D3d for the two compounds that were more stable by 4 and 23 kcal/mol respectively.

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.

AM1 Structures of Helvetane and Israelane
(ball and stick model of helvetane) (ball and stick model of israelane)
(spacefilling model of helvetane) (spacefilling model of israelane)

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: [12]-prismane, helvetane and israelane share IUPAC name tridecacyclo[,13.03,12.04,11.05,10.06,9.07,20.08,19.015,24.016,23.017,22.018,21]tetracosane


  1. G. Dinsburg (a.k.a. D. Ginsburg), Nouv. J. Chim. 6 (1982) 175.
  2. W. Li, T. Y. Luh, S. W. Chiu, Croat. Chem. Acta 58 (1985) 1.
  3. J. M. Schulman, M. A. Miller, J. Mol. Struct. (Theochem) 40 (1988) 133.

*Chime can be obtained from MDL Information Systems, Inc.

Mitchell Miller, MDL Information Systems, Inc.

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