Substituent effects on ¹H and ¹³C NMR chemical shifts in styryl fluorenyl and styryl biphenyl ketones

Abstract

Several substituted styryl 2-fluorenyl ketones and styryl 4-biphenyl ketones have been prepared and their ¹H and ¹³C NMR spectra recorded. While the chemical shifts of β-protons and β-carbons in styryl 2-fluorenyl ketones exhibit good correlation with Hammett σ <i>&nbsp;</i>constants, those of α-protons and α-carbons fail in such correlations. The susceptibility of the chemical shifts of β-protons and β-carbons to the electrical effects of substituents in

styryl 2-fluorenyl ketones is less compared to that found in styryl 4-biphenyl ketones for the corresponding protons and carbons. The failure observed and the low susceptibility found are

attributed to the contribution of resonance involving methylene bridge.