Expandability of a long C-O bond by a scissor effect in acenaphthofuran.

The angle strain induced by ring annulation on a spiro-type naphthofuran weakens its C(sp3)-O bond at the opposite peri-position and endows expandability, so that quite different bond lengths [1.493(3)-1.526(6) Å] are determined for the elongated C(sp3)-O bond of the corresponding spiro-acenaphthofuran derivative upon X-ray analyses of its pseudopolymorphs.

New insights into the hexaphenylethane riddle: formation of an α,o-dimer.

Upon reduction of a 1H-cyclobuta[de]naphthalene-4,5-diylbis(diarylmethylium) species, a new CC bond is formed between the Cα and Cortho atoms of the two chromophores, which presents an unprecedented coupling pattern for the dimerization of two trityl units. By attaching an annulated cyclobutane ring at the opposite peri position of the naphthalene core, the distance between the Cα  carbon atoms was elongated beyond the limit of σ-bond formation through "scissor effects". The suppression of Cα Cα bond formation, which would lead to hexaphenylethane-type compounds, is key to the first successful isolation of the α,o-adducts.

Preparation and structure of acenaphthylene-1,2-diyldi(9-acridine) derivatives with a long C=C bond.

Due to purely steric effects of acridine units, acenaphthylene-1,2-diyldi(9-acridine) has a long C=C bond [1.3789(19) Å] while maintaining its sp(2) hybridized nature and bond order.