Crystal Sturcture and Direction of the Polar Axis of (-)-(!S)-Pionic Acid β-Oxime

Article abstract of DOI:10.1107/S0108768189003800

(-)-(1S)-cis-3-(Hydroxyiminoethyl)-2,2-dimethyl-cyclobutylacetic acid, C10H17NO3, Mr=199.25, monoclinic, P21, a=14.632(8), b=12.193(3), c=7.103(2)A, β=112.54(3) deg, V=117O.5(8)A3, Z=4 (two independent molecules in the asymmetric unit), Dx=1.130 g/cm3, MoKα, λ=0.7l073 A, μ=0.69 1/cm, F(000)=432, T=295 K, R=0.047 for 1156 observed reflecitons 2.5?(i)> and 257 parameters.Calculation suggests that he polarization of molecules of the (-)-enantiomer, oriented as in the crystal, is such that the positive end of the crystal's electric dipole is toward the + end of the b axis; conversely, for the (+)-enantiomer the polarization is in the opposite sense with the electrically positive end of the crystal dipole toward -b.This electrical polarization, due to te molecular orientation found from the crystal structure determination of the crystal produced by heating (the pyroelectric effect) as determined by the Kundt-Buerker powder test.Thus, as has been found in previous examples, the orientation along the polar axis of the electric dipole induced by heating is the same as the orientation of the polarization of the crystal deduced from the X-ray structure.