Crystal structures of crown ethers containing an alkyl diarylphosphinate or a diarylphosphinic acid unit

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 1 B b exciton couplet was observed in the ECD spectrum of monomeric ( R,R )- 6 in MeOH and H 2 O 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.