Stereospecific Spin–Spin Coupling between Hydroxyl Protons and ¹⁹F Nuclei in <i>o</i>-, <i>m</i>- and <i>p</i>-Fluorophenol Derivatives. "Through-space" Interactions via the Hydrogen Bond

Abstract

Under conditions of slow intermolecular hydroxyl proton exchange 6 J p OH,F &lt; 0, 5 J trans OH,F &gt; 0, 5 J cis OH,F &lt; 0, 4 J o OH,F &lt; 0 in fluorophenol derivatives. 5 J m OH,F is remarkably insensitive to intrinsic substituent effects, yields accurate values of conformational populations of m-fluorophenol derivatives and can be used to demonstrate a buttressing effect on the strength of the relatively weak [Formula: see text] hydrogen bond. 4 J o OH,F displays a stereospecific dependence opposite to that of other couplings from a side-chain proton to a ring fluorine nucleus, is apparently very sensitive to the distance between proton and fluorine nucleus and is cited as an example of a negative through-space coupling mechanism. Approximate molecular orbital calculations give some support to the last suggestion.