COMMUNICATIONSgraphic) molecular site symmetry is only C, (T), the molecular geometry (Fig. I) The crystal structure of 1,3,5,7-tetra-tert-butyl-s-indacene 1 as determined at room temperature"] shows effective DZh symmetry of the carbon skeleton. Similarly, the presence of only four 13C-NMR signals that show no perceptible line broadening down to -130°C for the twelve C atoms of the perimeter is consistent either with a very low energy barrier between the valence isomers or with a completely delocalized twelve-electron 71 system. According to calculations"' ( M I N D 0 / 3 method), the energy barrier is only about 8 kJ mol-' for the tetrasubstituted molecule 1, although it is considerably larger for the parent hydrocarbon."]We now report results of a new, more accurate low-temperature (100 K) X-ray analysis of 1, which substantiate and extend these indication^.^^."^ Although the (crystallo-I*] Prof.

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The syntheses of threefold acceptor-substituted 1,3,5-triaminobenzene derivatives 2 ± 6 and their crystal structure analyses are described. As acceptors, nitro, trifluoromethylsulfone, and alkylsulfone groups are employed. The combination of hydrogen bonding, arene´´´arene and F´´´F contacts leads to remarkably similar solid-state layer structures for sterically quite dissimilar molecules.

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between the parallel arranged acetylene units cause a cisoid bending (bond angle 171.7"). The homologous l,7-cyclododecadiyne (4) shows a twisted chair-chair like conformation in which both acetylene moieties cross each other by an angle of 24". The cisoid deformation of the acetylene moieties (173.8') is due to the unfavourable conformation of 4. The photoelectron (PE) spectrum of 3 shows four clearly split x bands, while in the PE spectrum of 4 only two strongly overlapping bands are found in the low energy region. The difference in the PE spectra between 3,4 and 1,5-cyclooctadiyne (2) is rationalized as due to conformational effects (3-4) and a/o interactions (2-3), respectively.Nachweis des Einflusses der Bruckenlange bei Acetylenen studierten wir die entsprechend uberbriickten 1,8-Diethinylnaphthaline 12). Als Methode der Wahl erwies sich die Photoelektronen-(PE)-Spektroskopie. Bedingt durch die Uberlagerung der n-Banden des Naphthalinrings und der Acetyleneinheiten konnten die in Abb. 1 gemachten Voraussagen nur durch den Vergleich mit Modellrechnungen plausibel gemacht werden.Wesentlich gunstiger sollte sich der Vergleich zwischen 1 3 -Cyclooctadiin (2), 1,6-Cyclodecadiin (3) und 1,7-Cyclododecadiin (4) gestalten, da hier die storenden rc-Banden des Naphthalinsystems nicht mehr vorhanden sind. Wahrend die Synthese von 2 und 4 bereits beschrieben ~u r d e~,~) , war 3 noch unbekannt. Im folgenden berichten wir uber die Synthese von 3 sowie uber die Strukturen und die PE-Spektren von 3 und 4. Synthese von 1,bCyclodecadiin (3)Zur Synthese von 3 wurden zwei Wege eingeschlagen. uber einen der beiden berichteten wir in einer Kurzmitteilung? Ausgehend von 4,4,9,9-Tetramethoxy-l,6-cyclodecadien (S), das aus Naphthalin durch Birch-Reduktion, OxiChem. Ber. 121, 735-740 (1988)

Racemic crystalline tetra(p-bromophenyl)ethylene was converted into chiral inclusion crystals in the solid state by contact with gaseous achiral guest compounds.Chiral crystallization of achiral molecules in the absence of any external chiral source is of special interest not only for "socalled" absolute asymmetric synthesis 1 but also for its relationship to the prebiotic origin of chirality. 2 Such chiral crystals have been obtained previously during crystallization of achiral substrates from their solutions. We have now found that chiral inclusion crystals can be obtained by treatment of a racemic host compound with the vapor of achiral guest compounds. This is the first example of the formation of chiral inclusion crystals from achiral components through gas-solid inclusion complexation.

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