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syn‐ar,ar ′‐Difluorometacyclophanes: Strong 19 F, 19 F Spin—Spin Interactions Transmitted through Space
Author(s) -
Ernst Ludger,
Ibrom Kerstin,
Marat Kirk,
Mitchell Reginald H.,
Bodwell Graham J.,
Bushnell Gordon W.
Publication year - 1994
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19941270623
Subject(s) - chemistry , spin (aerodynamics) , space (punctuation) , fluorine , crystallography , series (stratigraphy) , atomic physics , physics , thermodynamics , paleontology , linguistics , philosophy , organic chemistry , biology
The close approach of the fluorine nuclei in the difluorinated syn ‐[3.3]metacyclophanes 1, 2 and their [2.2] analogues 3, 4 leads to strong 19 F, 19 F spin‐spin interactions which obey a through‐space mechanism. The geometries of 1–4 were estimated by MM2 molecular mechanics computations, those of 1 and 3 were also determined by X‐ray structural analyses. The decrease of the F,F internuclear distance in the series 1, 2, 3, 4 (2.78–2.48 Å) correlates with an increase of J (FF) from +42.1 to +99.2 Hz. It follows that, for a given distance d (FF), J (FF) is up to twice as large as a previous empirical correlation has assumed and even larger with respect to earlier theoretical calculations. Only weak F,F spin interaction occurs in 8 , the anti isomer of 4 .