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By means of gas chromatography and mass spectrometry, Manicone, (4E)‐4,6‐dimethyl‐4‐octen‐3‐one (1), was identified as the main component of the mandibular gland secretion of the ant Manica rubida. In addition the presence of homomanicone (2), bishomomanicone (3), normanicone (7), and a few aliphatic aldehydes and ketones was also evident in the gland. Racemic 1, 2, and 7 and optically active dihydromanicone (4), were synthesized. The (S) configuration of 1 was determined by complexation gas chromatography, on a chiral phase, of 4 as well as of the hydrogenation products of racemic and natural 1.

ChemInform Abstract Manicone (Ia) is identified as the main component of the title species. In addition the presence of homomanicone (Ib), bishomomanicone (Ic), normanicone (Id), and a few aliphatic aldehydes and ketones is also found in the gland. Racemic (Ia), (Ib) and (Id) as well as optically active dihydromanicone (XI) are synthesized as outlined in the scheme. The (S)-configuration of (Ia) is determined by complexation gas chromatography, on a chiral phase, of (XI) as well as of the hydrogenation products of racemic and natural (Ia).

stretching vibration, in accord with a one-minimum poten-The present discussion is relevant not only in the context of the geometrical structure of benzene, it has even more general implications in connection with questions as to the CC bond length alternation and double bond localization (and the related aromaticity problems), respectively, in annulenes of arbitrary ring size, bridged annulenes, and polycyclic x systems with condensed rings. In particular, this holds for analyses of such problems by means of routine X-ray diffraction studies: Caution is obviously called for!13. 161