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19 F n.m.r. spectrum of hexafluoroquinazoline long‐range inter‐ring FF coupling constants
Author(s) -
Matthews R. S.
Publication year - 1977
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270090606
Subject(s) - coupling constant , delocalized electron , ring (chemistry) , spectral line , chemistry , nitrogen , crystallography , atomic physics , physics , organic chemistry , particle physics , astronomy
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.