2,11-Dibromo-5,8-dibut-yl[4]helicene

Abstract

A racemic mixture of the title compound, C(26)H(26)Br(2), a brominated [4]helicene, crystallizes, forming columns of stacked mol-ecules. There are two crystallographically unique mol-ecules in the asymmetric unit, both with the same helical handedness. As is typical with helicene congeners, the unique mol-ecules show short inter-atomic contacts between H atoms at the fjord region, with H⋯H distances of 1.87 and 1.94 Å. Mol-ecules with the same helical handedness segregate in the crystal packing, forming homochiral columns. The stacked mol-ecules are piled in a column with alternate orientations. The shortest C⋯C distance in the stacked mol-ecules is 3.306 (4) Å.

Fig. 1.

Molecular structures of the title compound with displacement ellipsoids drawn at the 50% probability level. Two non-equivalent molecules for (P)-form are shown. Note that the two structures differ only slightly at the methylene chain and that the enantiomeric (M)-form can be found as the mirror geometries.

Fig. 2.

Packing structure of the title compound, viewed along the b axis. The carbon atoms of enantiomers are colored differently. Color code: C for (P)-form = green, C for (M)-form = blue, Br = brown. Hydrogen atoms are omitted for clarity. Note that one colomn comprise single enantiomeric molecules with an alternate stack of two crystallographically unique molecules.

Fig. 3.

Stacking structure of the (P)-form. Hydrogen atoms are omitted for clarity.