title: The surprising sp rotameric structure of 9-methyl-9-pivaloylfluorene
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).
authors: Department of Chemistry and Biochemistry, Southern Illinois University-4409, Carbondale, IL 62901, USA.
authors: CY
authors: Meyers
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authors: Lutfi
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authors: Varol
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authors: Hou
authors: PD
authors: Robinson