Crystal structures and vibrational spectra of racemic and chiral 4-phenyl-1,3-oxazolidine-2-thione

Abstract

The crystal structures of (rac)- and (R)-4-phenyl-1,3-oxazolidine-2-thione (4-POT) have been determined by X-ray diffraction. The structure of (rac)-4-POT is monoclinic P21/n with a = 11.9096(9) A, b = 5.9523(6) A, c = 12.3563(8) A, β = 91.054(6)°, V = 875.8(1) A3, and Z = 4. The structure of (R)-4-POT is orthorhombic P212121 with a = 7.7197(6) A, b = 21.603(2) A, c = 5.4613(9) A, V = 910.8(2) A3, and Z = 4. (rac)-4-POT and (R)-4-POT crystals are shown to have different hydrogen-bonding patterns. In the racemic crystals, the enantiomeric (R)- and (S)-4-POT molecules are connected to form a cyclic dimer via the N–H ⋅ ⋅ ⋅ S hydrogen bond of the cis thioamide moiety [N ⋅ ⋅ ⋅ Si 3.438(2) A, N–H ⋅ ⋅ ⋅ Si 176(2)° symmetry code: (i) 1 − x, 1 − y, 1 − z]. In the chiral (R)-4-POT crystals, the N–H ⋅ ⋅ ⋅ S intermolecular hydrogen bond forms a zigzag chain around the twofold screw axis [N ⋅ ⋅ ⋅ Sii 3.347(3) A, N–H ⋅ ⋅ ⋅ Sii 161(3)° symmetry code: (ii) 1/2 + x, 1/2 − y, 2 − z]. Observed difference of 46°C in the melting points between the (rac)-4-POT and (R)-4-POT crystals is correlated with difference in the crystal packing. Vibrational spectra of (rac)- and (R)-4-POT crystals are discussed both in the solid state and in solution.