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Communications to the Editor 1317(2) The reaction of TaCp(CHCMe3)CI2 with 08 50 =0 2 gives C6H5CH=CDCHDCMe3, consistent with this proposal.(3) (a) The Ti4+ metallocycle, TiCp2(C4H8), decomposes to give ethylene and 1-butene; metallocyclopentane complexes are more stable than their acyclic analogues since /3-hydride elimination is suppressed, probably for steric reasons: J.

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The position of equilibrium between the title compounds, which are valence-bond isomers, is governed by the magnitude of the van der Waals' attraction between the two alkyl groups. This is calculated (MMPZ) to favor the 1,6 isomer by less than 0.02 kcal/mol in the case where the two groups are methyl and more than 1.07 kcal/mol in the case where the two groups are tert-butyl.

Copolymers of ethylene and propylene in which none of the propylene units are reversed have low levels of crystallinity over the entire range of composition. Molecular mechanics calculations indicated that the polyethylene-type planar-zigzag conformation and the polypropylene-type helical conformation would have similar energies in copolymers containing 33-55 mol % ethylene. Measurements by X-ray diffraction and differential scanning calorimetry showed that samples in this range contained both kinds of crystals. When a copolymer of propylene with 36 mol % ethylene was incorporated in a blend of isotactic polypropylene and low-density polyethylene, the polyethylene phase was more finely dispersed, and the interfacial adhesion and notched Izod impact strength were improved. These effects were attributed to the ability of the copolymer to cocrystallize with both homopolymers.