TOWARD HEXAPHENYLETHANE - STRUCTURE AND DECOMPOSITION OF CRYSTALLINE TRIPHENYLMETHYL IODIDE

Triphenylmethyl iodide (C19H15I) crystallizes in the monoclinic system : a = 15.919(6) Angstrom, b = 10.826(6) Angstrom, c = 19.397(11) Angst rom, beta = 114.86(4)degrees, space group C2/c, Z = 8, In the structur e, heterochiral propeller molecules are interdigitated. This arrangeme nt, coupled with earlier reports of the thermal instability of triphen ylmethyl iodide, suggested a convenient, topochemically controlled, so lid-state synthesis of the elusive hydrocarbon hexaphenylethane. Cryst als of the C-13(methyl)-labeled triphenylmethyl iodide were heated to 100 degrees C in a rotor spinning at the magic angle within an NMR spe ctrometer. Spectral changes and accompanying analyses by plasma desorp tion mass spectrometry, calorimetry, and ESR spectroscopy reveal that the major product in the decomposition is triphenylmethane, produced b y hydrogen atom abstractions from neighboring triphenylmethyl radicals , that subsequently oligomerize, These data provide a new view of the thermal stability of triphenylmethyl iodide in the solid state and an old view of the accessibility of hexaphenylethane.