19F nuclear magnetic resonance studies of aromatic compounds. Part II. The 19F chemical shifts in meta- and para-substituted fluorobenzenes, and 4-substituted 3′- and 4′-fluoro-trans-stilbenes

Abstract

A detailed study has been made of the effects of substituents, X, upon the shielding of ¹⁹F nuclei in series of meta and para-X-fluorobenzenes, 4-X-4′-fluoro-trans-stilbenes, and 3′-fluoro-4-X-trans-stilbenes. The correlation of substituent chemical shifts for ¹⁹F nuclei in fluoroaromatic compounds with reactivity parameters is examined, and a reassessment is made of the Taft and Swain and Lupton separation of polar substituent effects into field/inductive and resonance components.