COMMUNICBTIONS TO THE EDITOR 4659 (C1zHlof+, 4n + 2 ?r-electrons), but proton abstraction has resulted in the synthesis of heptalene ((212-HID, 4n n-electrons), as described in another Communication.(9) Partial support of this work by the U. S. Army Research Offme is gratcfully acknowledged; D. J. B. is indebted t o the Standard Oil Company (California) for a fellowship held during a portion of this research.

the lowest charge density on the oxygen of the compounds considered in Table I. Thus, the CNDO/2 theory does tend qualitatively to anticipate the An + 2 rule in cross-conjugated systems by predicting slightly enhanced tt polarization in tropone and cyclopropenone, and a low tt polarization for cyclopentadienone, but attributes to this rule a considerably less significant position for these systems than organic chemists are accustomed to. There are numerous additional molecules for which it is possible to write dipolar resonance structures, which generate cyclic An + 2 tt systems.(3) (a) D.

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