High-resolution proton magnetic resonance spectra of fluorene and its derivatives. Part III. 9-Substituted fluorenes

Abstract

¹ H N.m.r. spectroscopic measurements at 60 MHz are reported for solutions in [²H] chloroform, carbon tetrchloride, [²H₆] acetone, and [²H₆] dimethyl sulphoxide of forty three 9-substituted fluorenes. In these and other 9-fluorenes, extensive comparison of the chemical shifts, δ₉, of H(9), and also the shift relative to that of fluorene with such parameters as polarisability, dipole moment, Hammett constants, and bulk revealed a correlation only with electronegativity. Of the aromatic shifts, δ₄ tended to shift to high field with the ‘inductive’ Hammett constant, σ_I^meta, and δ₁ to low field with both negative anisotropy of susceptibility, Δ_χ, and size of substituent. Otherwise, aromatic shifts appeared to be independent of other Hammett constants, group electronegativity, O, dipole moment, and covalent radius. No evidence was found for enol forms in [²H] chloroform solutions of any of the 9-COR-fluorenes examined. Coupling constants between H(9) and the substituent X are in fair agreement with the corresponding CH₃X couplings, provided due allowance is made for the electronegativity of fluorene and for the conformation of the substituent. There is an unusual CH–SO₂–CH coupling of 1·0 Hz in methyl 9-fluorenyl sulphone.