ISSN:
0947-3440
Keywords:
Calculations, force field
;
Dynamic NMR spectroscopy
;
Chiral conformations
;
Chiral ion pairs
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The synthesis of 2,3-didehydro[15]crown-5 and -[18]crown-6 derivatives 4a, b with vicinal α-naphthyl groups at the double bonds starting from α-naphthoin (3) is described. The barriers to rotation of the naphthyl groups were probed by MM2 and by dynamic 1H-NMR spectroscopy. An achiral syn and a chiral anti conformation were experimentally observed at -90°C for the free ligands and at -40°C for the complexes. The experimental ΔG≠ and the calculated ΔH≠ values are in fair agreement. The barriers are substantially higher in the alkali metal complexes than in the free ligands. In the presence of racemic and potassium S-(+)-mandelate non-equilibrating ion pairs with 4b were observed by low-temperature 1H-NMR spectroscopy for the anti conformation.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.199619961021
