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Conformers and Rotamers of (±)‐ trans ‐2,3‐Bis(2‐naphthyl)‐15‐crown‐5 and ‐18‐crown‐6 and Their Alkali Metal Complexes
Author(s) -
Merz A.,
Gromann L.,
Karl A.,
Parkanyi L.,
Schneider O.
Publication year - 1998
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199802)1998:2<403::aid-ejoc403>3.0.co;2-q
Subject(s) - conformational isomerism , chemistry , alkali metal , nuclear magnetic resonance spectroscopy , crown (dentistry) , metal , crystallography , spectroscopy , stereochemistry , molecule , organic chemistry , materials science , physics , quantum mechanics , composite material
The conformations of (±)‐ trans ‐2,3‐Bis(1‐naphthyl)‐15‐crown‐5 ( 1 ) and ‐18‐crown‐6 ( 2 ) are investigated by MM2 and dynamic 1 H‐NMR spectroscopy. The most stable conformation is the diequatorial one in both the free ligands and the alkali metal complexes 1 · NaClO 4 and 2 · KClO 4 . Three rotamers, pseudo ‐ aa, pseudo ‐ ee, and pseudo ‐ ae, with respect to the spatial arrangement of the naphthyl groups, were found as calculated minima by MM2 and experimentally by low‐temperature NMR, with fair agreement of the rotational barriers. In the cation‐reinforced crowns the rotation rates are significantly diminished. The distribution of the rotamers depends on the size of the crown and its state, free or complexed.