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Updated: Jul 31, 2026

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
Published on: September 26, 2016
The surprising sp rotameric structure of 9-methyl-9-pivaloylfluorene
1Department of Chemistry and Biochemistry, Southern Illinois University-4409, Carbondale, IL 62901, USA.
Abstract:
Methylation of 9-lithiated ap-9-pivaloylfluorene, (I), as well as pivaloylation of 9-lithiated 9-methylfluorene provided rotationally stable sp-9-methyl-9-pivaloylfluorene, (III), C(19)H(20)O, which lies about a crystallographic mirror plane. Fluorene (I) exists exclusively in the ap configuration in solution (NMR) as well as in the crystalline state, reflecting the unfavorable interaction between the tert-butyl and fluorene-ring pi electrons in the sp configuration. The existence of (III) exclusively in the sp configuration indicates that, in this case, the interaction between the tert-butyl group and the fluorene-ring pi electrons provides relatively more thermodynamic stability than the steric interaction between the tert-butyl and 9-methyl groups (ap configuration).
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