19 F n.m.r. spectrum of hexafluoroquinazoline long‐range inter‐ring FF coupling constants

The 19 F n.m.r. spectrum of hexafluoroquinazoline has been analyzed giving the signs and magnitudes of all but two of the coupling constants, and supporting the analyses of the 19 F n.m.r. spectra of heptafluoroquinoline and heptafluoroisoquinoline. Long range FF inter‐ring coupling constants are a guide for assessing π‐electron delocalization pathways. In addition, nitrogen in the β position enhances the distant F‐5, F‐7 meta ‐coupling constant, implying a π‐contribution to J ( FF ) meta . A rationalization of changes in peri ‐coupling constants is also presented. The observed changes appear to be the sum of two effects: (i) ring contraction by the insertion of shorter CN bonds into the aromatic ring and (ii) a secondary effect which is dependent on the existence of a β‐nitrogen, adjacent to the peri nuclei.