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dibromide was isolated by removing through fractional recrystallization (of a bromination product) at Dry Ice temperature (repentane) as much of the solid 3,6 isomers as possible and then flash distilling [bp 40°( 0.07 mm)] a small amount of the liquid. Only a very small amount of the pure isomer (nearly free of the 3,6 isomers) could be isolated with each distillation. The liquid (pure) was found to be extremely labile and rearranged to the 3,6 isomers.The liquid dibromide was assigned the trans 3,4 structure (4) on the following basis: its boiling point was essentially identical with those of the 3,6 isomers; its melting point was much lower than those of the 3,6 isomers, which suggests lower molecular symmetry; the C-H absorption bands in the ir spectrum were very similar to those of the 3,6 isomers; and it (4) rearranged on standing in CCL to give 5 and 6. [The liquid isomer (4), 5, and 6 all rearranged to identical equilibrium mixtures.] Also, nmr spectra of mixtures containing 4 did not show any signals inconsistent with its structure. Unfortunately, signals attributable to it were masked by the overlapping signals from the other two isomers, even at 220 MHz. Nmr spectra of both pure solid