ENANTIOMER ASSOCIATIONS IN THE CRYSTAL-STRUCTURES OF RACEMIC AND XYPHENYL)-2,3-DIHYDRO-1,5-BENZOTHIAZEPIN-4(5H)-ONE

The crystal structures of racemic and xyphenyl)-2,3-dihydro-1,5-benzot hiazepin-4(5H)-one (C16H15NO3S) have been determined in order to compa re the interactions between molecules of the same and opposite chirali ty. The enantiomeric associations observed in these two crystal struct ures are analysed, relating the differences to those found in the equi valent diastereomers, (2R,3R) and/or (2S,3S). Single-crystal X-ray dif fraction data were collected at low temperature with Cu K alpha radiat ion (lambda = 1.54184 Angstrom). Optically active: monoclinic, space g roup C2, with a = 24.726(3), b = 5.2426(5), c = 12.0726(12) Angstrom, beta = 112.979(9)degrees, V = 1440.8(5) Angstrom(3), Z = 4, D-x = 1.38 9 g cm(-3), mu = 20.35 cm(-1), the refinement on 2918 observed reflect ions gave R = 0.0271. Racemic: monoclinic, space group P2(1)/n, with a = 13.308(3), b = 4.8474(8), c = 22.130(4) Angstrom, beta = 91.782(14) , V = 1426.9(5) Angstrom(3), Z = 4, D-x = 1.403 g cm(-3), mu = 20.54 c m(-1), refined to R = 0.0318 for 2753 observed reflections. An intramo lecular hydrogen bond between the hydroxy and carbonyl groups appears to stabilize the benzothiazepinone ring in the (P,2S,3R) boat conforma tion with the hydroxy and methoxyphenyl substituents in equatorial pos itions. In both crystal structures two N-H ... O hydrogen bonds connec t the molecules into dimers. In the optically active compound the two molecules are related by a twofold axis, in the racemate by an inversi on centre. The racemate contains an additional hydrogen bond which is reflected by its higher melting enthalpy compared with the optically a ctive compound. The difference in the chiral discrimination in the sol utions of the cis-and trans-diastereomers does not appear to have its origin in the strong (O-H ... O, N-H ... O) hydrogen bonds, but rather in the weak (C-H ... O) interactions.