Barrier to Internal Rotation in 2,6-Dichlorobenzal Iodide and some α,α′-m-Xylyl Halides. Experimental Evidence for the Transition State Conformation in Benzal Halides

Abstract

The barriers to internal rotation in the α,α′-di-X-2,4,5,6-dichloro-m-xylenes (X = Cl, Br, I ) are determined by proton magnetic resonance bandshape analyses. Their magnitudes are experimental evidence for the calculated conformation of the activated rotational state of the benzal halides, in which the C—H bond of the side chain is predicted to lie in a plane perpendicular to the aromatic nucleus. The synthesis and the barrier to rotation in 2,6-dichlorobenzal iodide are reported.