The Cubane Cage - a Sensible Probe for Substituent Effects on a Four-membered Ring

✍ Scribed by Irngartinger, Hermann ;Strack, Stefan ;Gredel, Frank

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 517 KB
• Volume: 1996
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.199619960304

✦ Synopsis

The crystals of methyl 4-fluoro-1-cubanecarboxylate ( l ) , methyl 4-chloro-1-cubanecarboxylate (2) and methyl cubanecarboxylate (5) are isomorphous to each other as are the crystals of methyl 4-bromo-1-cubanecarboxylate (3) and methyl 4-iodo-1-cubanecarboxylate (4). As a result of the space groups P2,/m and Pnma, respectively, all molecules lie in a crystallographic mirror plane. Therefore, the methoxycar-bony1 group is exactly planar, and the carbonyl fragment is in an eclipsed position to the cubane skeletal bond C2-C7.

The electronic effects of the halogen atoms, in particular fluorine and chlorine, give rise to a shortening of the vicinal skeletal bonds. In contrast, the methoxycarbonyl groups causes a lengthening of the vicinal skeletal bonds C2-C6 and C2-C6A which are not in an eclipsed conformation. Ab initio calculations at the 6-31G* level of compounds 1, 2, and 5 confirm the experimental results.