J. Am. Chem. SOC. termediate in MTG chemistry, but the observation that 1 can form in HZSM-5 from a known MTG intermediate removes a major objection to mechanisms such as those in Scheme I. Furthermore, with the ability to generate significant quantities of 1 in HZSM-5, it should be possible to further explore these mechanisms.We report the observation of helix-sense reversal of linear chloral oligomers (degree of polymerization, DP = 4-6) in solution by NMR spectroscopy and determination of the inversion barrier, which has been found to be dependent on DP.Some synthetic polymers such as polychloral,* poly(triphenylmethyl metha~rylate),~ and poly(tert-butyl i~ocyanide)~ are known to show optical activity arising entirely from conformational asymmetry (macromolecular asymmetry) when the polymers are prepared by helix-sense selective polymerization. The helix of the optically active polymers seems to be rigid in s o l~t i o n~~~ or slowly undergoes racemization to a nearly 1:l mixture of the rightand left-handed helices.' The helical conformation of polyisocyanates is less stable, and consequently, right-and left-handed states exist In equilibrium.* Although the one-handed helicity

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