STERICALLY CONGESTED MOLECULES .4. FRONT STRAIN ALONG A C-C DOUBLE-BOND IN THE CRYSTAL-STRUCTURE OF [1-(1,1,3,3-TETRAMETHYLINDAN-2-YLIDENE)-1-(TRIMETHYLSILYL)METHYL] 2-TRIMETHYLSILYLPHENYL THIOETHER

The 1,1,3,3-tetramethylindan-2-ylidene moiety which occupies one end of the C-C double bond in the title molecule (1) exhibits only small deformations in the solid-state structure despite its repulsive interactions with the heteroatoms at the other end. Front strain along this double bond causes remarkable extensions of angles and bond lengths involving those heteroatoms. The exocyclic olefinic carbon atom is slightly pyramidalized but the C-C double bond is not elongated. The low flexibility of the former moiety is suggested to be a transferable property for the visualization of front strain.