Knowledge Bank

The complexes formed between the hydrogen halides and a variety of substituted cyclopropanes have been isolated and characterized in inert matrices. The complexes may be divided into two classes, those in which the cyclopropane ring bears an electron-withdrawing group as a substituent and those in which the substituent is an electron donor. Methyl-substituted cyclopropanes fall into the latter group. These complexes were characterized by an intense hydrogen halide stretching mode that was shifted to lower energies by up to $100cm-1$ from that of the uncomplexed position. In addition, perturbed vibrational modes of the methyl-substituted cyclopropane ring were observed. These results are analogous to those obtained for the the H-X-cyclopropane complexes and suggest that the complexes are similar in structure. The results for cyclopropyl bromide and cyanide were very different. An intense hydrogen halide stretching mode could be observed, but the only perturbed modes of the substituted cyclopropane corresponded to a perturbed C-Br or C-C-N vibrational mode. These results suggest that the complex formed between cyclopropanes containing electron withdrawing groups as substituents and the hydrogen halides are structurally different than the HX-cyclopropane complexes. These studies are being continued and a wider variety of substituted cyclopropanes are being examined.