Comparison between Theoretical and Experimental Deformation Density of 1,3,5,7‐Tetra‐ t ‐Butyl‐S‐Indacene

1,3,5,7‐Tetra‐ t ‐butyl‐s‐indacene is a twelve‐membered fused‐ring compound; the stabilization of the compound by bulky t ‐butyl groups is discussed. The distribution of bonding electron density is depicted in terms of deformation density using the experimental X‐X method, a multipole expansion model and a calculation according to the extended Hückel molecular orbital method (EHMO). The molecules crystallize according to the space group P2 1 /n with cell parameters a = 9.700(3), b = 11.746(3), c = 10.858(2)Å, β = 107.67(2)°, Z=2 at 100K. The molecule has a center of inversion( ) and belongs to the symmetry point group C i . The packing of two unique t ‐butyl groups in the asymmetric unit appears significantly different. However, the map of deformation density in the plane of the ring shows pseudo D 2h symmetry. The accumulation of density at the midpoint of the bonds is observed as expected. The theoretical deformation densities agree with the experimental ones. Analyses of the molecular‐orbital wavefunctions provide a good illustration of the aromatic π‐electron system. A theoretical study of a series of substituents (‐H, ‐ CH 3, ‐ t ‐butyl ) on s ‐indacene illustrates the stabilization effect of the t ‐butyl group on the 12‐π‐electron ring system.