Effects on Cyclopropane Geometry of Aromatic Substituents in the Bisected Conformation. The Structures of Spiro[cyclopropane‐1,9′‐[9H]fluorene] and 2,2‐Dichlorospiro[cyclopropane‐1,9′‐[9H]fluorene]

The structures of spiro[cyclopropane‐1,9′‐[9H]fluorene] ( 1 ) and 2,2‐ dichlorospiro[cyclopropane‐1,9′‐[9H]fluorene] ( 2 ) have been determined by conventional single‐crystal X‐ray diffraction techniques. Compound 1 crystallizes with 32 molecules in the unit cell in space group C 21 2 v – Iba 2 of the orthorhombic system in a cell of dimensions a = 42.228(23), b = 27.318(17) and c = 7.664(8) Å. Compound 2 crystallizes with four molecules in the unit cell in space group C 5 2 h – P 2 1 / c of the monoclinic system in a cell of dimensions a = 8.451(3), b = 8.960(3), c = 15.882(5) Å and β = 97.31(1)°. The structures of 1 and 2 have been refined by full‐matrix least‐squares techniques to conventional R indices of 0.055 and 0.049, respectively. Relative to the bridgehead position, the cyclopropane ring in 1 contains a short distal bond of average value 1.496(9)Å and lengthened vicinal bonds averaging 1.531(11)Å. This geometry agrees qualitatively with a simple molecular orbital model for charge transfer from cyclopropane to an aromatic π‐system held in the bisected conformation. The cyclopropane ring in compound 2 contains C–C bond lengths of 1.537(3), 1.517(3) and 1.475(3) Å. These values cannot be explained by summing the expected changes induced by the aromatic and halogen substituents.