Crystal structures of crown ethers containing an alkyl diarylphosphinate or a diarylphosphinic acid unit
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This paper describes the structures of pseudo-18-crown-6 compounds (2, R,R-4 and 5) in the crystals together with theoretical calculations of the electronic circular dichroism (ECD) spectra. The achiral macrocyclic phosphinic acid 5 forms hydrogen-bonded dimers in the crystal. The O1–O2 distance (2.489 Ǻ) indicates strong H-bondings. The conformations of the macrorings of the achiral phosphinate 2 and the monomers of the achiral phosphinic acid 5 are chiral. A comparison of the torsion angles of the achiral methyl phosphinate 2 and the monomeric units of achiral 5 indicates a similar geometry. The torsion angles of the chiral methyl phosphinate (R,R)-4 differ more significantly from those in achiral methyl phosphinate 2. A negative 1Bb exciton couplet was observed in the ECD spectrum of monomeric (R,R)-6 in MeOH and H2O as in the spectra of (R,R)-4 in all solvents. To support the idea that (R,R)-4 has basically the same conformation in the crystal and in solution, the ECD spectrum of (R,R)-4 was calculated using the geometry of the molecule in the crystal. The calculated ECD spectrum shows a reasonable agreement with the ECD spectra obtained in solution. This shows that the steric structure observed in the crystal is predominant in solution as well.
KeywordsCrown ethers Diarylphosphinates Diarylphosphinic acids X-ray analysis Computed ECD spectra
This work was supported by the Hungarian Scientific Research Fund (OTKA K62654 to P.H., PD71817 to V.F., PD71910 to T.T. and NI68466 to M.H.) and GVOP-3.2.1-2004-04-0345/3.0. The HPC Group computer facility, University of Szeged was used for several computations.
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