Effect of oxime substituents on 9-fluorenyl carbocations

✍ Scribed by Xavier Creary; Allison Wolf

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 125 KB
• Volume: 13
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/1099-1395(200006)13:6<337::aid-poc249>3.0.co;2-t

✦ Synopsis

9-Fluorenyl carbocations substituted with the oxime functional groups CH=NOCH 3 , CH 3 C=NOCH 3 , and i-PrC=NOCH 3 were generated by solvolyses of the corresponding chlorides in methanol. These cations form at rates which greatly exceed those of formation of the parent 9-fluorenyl cation. Relative rate data suggest that stabilization of 9-fluorenyl cations by CH=NOCH 3 is greater than stabilization by CH 3 C=NOCH 3 , which is in turn greater than that by i-PrC=NOCH 3 . Computational studies on these cations show that the oxime group is progressively rotated out of conjugation with the cationic center as the oxime group becomes larger. These rate and computational studies also suggest that 9-fluorenyl cations are not antiaromatic. They are essentially delocalized 'nonatetraenyl' cations, where formally antiaromatic resonance forms contribute little to the overall structure.