5-Membered rings molecular geometry

A systematic investigation of the ring-closing metathesis of 138 in the synthesis of a range of fourteen-membered ring lactams 139 and lactones has been reported by Weiler. The geometry of the resulting double bond was determined, the position of the olefin was broadly varied. The ratios obtained were compared to that derived from molecular mechanics calculations, Eq. (15), Table 4 [34]. 

Structural Details. For 1, the hexameric "drum" has idealized Sg molecular symmetry. The geometry of the stannoxane framework of the molecule consists of six-membered rings in a chair conformation. 

Se Sj2 CS2 and CS crystallize in the trigonal space group R3m. The molecular geometry ot he twelve-membered selenium sulfide ring molecule resembles that of Si2. The structure, however, is also disordered. The distribution of sulfur and selenium over the atomic sites is shown in Fig. 2. 

The 13-membered ring is available in a wide variety of unrestricted and restricted forms and undoubtedly represents one of the most thoroughly studied large-membered heterocycles. The size of the system s perimeter is sufficiently large to accommodate the presence of as many as three trans double bonds which, when strategically implanted, allow the molecular skeleton to adopt a rigidly flat or near-flat geometry in which to aromatically delocalize its 14 tr- electrons. 

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