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19F n.m.r. spectrum of hexafluoroquinazoline long-range inter-ring FF coupling constants

✍ Scribed by R. S. Matthews

Publisher
John Wiley and Sons
Year
1977
Tongue
English
Weight
400 KB
Volume
9
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

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 FF 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 CN 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.

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## Abstract Analyses of the ^19^F and ^1^H spectra of 1,2,3,4,5‐pentafluoro‐, 1‐bromo‐4,5,6,7,8‐pentafluoro‐, 1,2,3,4,5,6‐hexafluoro‐, and 1‐bromo‐3,4,5,6,7,8‐hexafluoro‐naphthalene are presented, and it is observed that the Fermi contact mechanism does not, simply, account for the long range coupl