THE STRUCTURE OF CYCLOPROPYLCARBINYL CATIONS - THE CRYSTAL-STRUCTURES OF PROTONATED CYCLOPROPYL KETONES

The structures of 1-cyclopropyl-1-hydroxyethylium hexafluoroantimonate, 9,1-(1′-methylcyclopropyl)-1-hydroxyethylium hexafluoroantimonate, 10, and 2-hydroxybicyclo[4.1.0]heptan-2-ylium hexachloroantimonate, 11, have been determined by single-crystal X-ray diffraction methods. The structures of these cations show major differences in their bond distances as compared to those of the neutral cyclopropyl ketones with the distal bonds in the cyclopropyl ring being shortened, the vicinal bonds lengthened, and the C(=0)-C(apex) bonds shortened. The cations adopt a conformation which is either bisected (9) or close to this (10, 11). The bond distances and conformation of these ions are fully consistent with those expected for a bisected cyclopropylcarbinyl cation. Comparison of the structures of these cations with those of other protonated cyclopropyl ketones reveals systematic changes in bond distances that can be related to the degree of charge delocalization into the cyclopropyl ring. Details of the structures of these cations and their crystal packing are discussed. © 1990, American Chemical Society. All rights reserved.