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1 H, 13 C and 19 F NMR study of 8‐fluoro‐ and 8,12‐difluoro[2.2]metaparacyclophane and of 9‐fluoro‐ and 9,14‐difluoro‐2,11‐dithia[3.3]metaparacyclophane
Author(s) -
Ernst Ludger,
Ibrom Kerstin
Publication year - 1998
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/(sici)1097-458x(199806)36:13<s71::aid-omr291>3.0.co;2-v
Subject(s) - chemistry , chemical shift , substituent , conformational isomerism , carbon 13 nmr , additive function , computational chemistry , fluorine 19 nmr , stereochemistry , derivative (finance) , coalescence (physics) , nuclear magnetic resonance spectroscopy , molecule , organic chemistry , physics , mathematical analysis , mathematics , financial economics , economics , astrobiology
The 1 H, 13 C and 19 F NMR spectra of 9,14‐difluoro‐2,11‐dithia[3.3]metaparacyclophane, 3F 2 , and its 9‐monofluoro derivative, 3F , and of 8,12‐difluoro[2.2]metaparacyclophane, 2F 2 , and its 8‐monofluoro derivative, 2F , were experimentally assigned as fully as possible. Two‐dimensional shift correlation techniques (H,H‐COSY, C,H‐ and F,H‐HETCOR) were applied and experimental 1 H and 13 C chemical shifts were compared with those predicted by assuming additivity of substituent chemical shifts (SCS). The difluoro compounds 2F 2 and 3F 2 occur as conformers with syn ‐ and anti ‐orientations of the fluorine substituents. The 19 F signals of 3F 2 undergo coalescence near 398 K (at 188 MHz) from which the barrier to syn / anti ‐interconversion is estimated as Δ G ‡ =77 kJ mol ‐1 . The shorter bridges in 2F 2 increase Δ G ‡ to a lower limit of 89 kJ mol ‐1 . A number of through‐space J (F,C) and J (F,H) couplings were observed. The small magnitudes of the J (F,F) couplings in 2F 2 and 3F 2 (0.4–1.9 Hz) do not allow their unambiguous classification as through‐space interactions. ©1998 John Wiley & Sons, Ltd.