N–H...S=C hydrogen bond in O-alkyl N-methoxycarbonyl thiocarbamates,

S. T. VALLEJOS; M. F. ERBEN; O. E. PIRO; E, E. CASTELLANO; C. O. DELLA VÉDOVA

POLYHEDRON

Elsevier

Año: 2009 vol. 28 p. 937 - 946

0277-5387

Pure O-methyl N-methoxycarbonyl thiocarbamate CH3OC(S)N(H)C(O)OCH3 (I) and O-ethyl N-methoxycarbonyl thiocarbamate, CH3CH2OC(S)N(H)C(O)OCH3 (II), are quantitatively prepared by the addition reaction between the CH3OC(O)NCS and the corresponding alcohols. The compounds are characterized by multinuclear (1H and 13C) and bi-dimensional (13C HSQC) NMR, GC–MS and FTIR spectroscopy techniques. Structural and conformational properties are analyzed using a combined approach involving crystallographic data, vibration spectra and theoretical calculations. The low-temperature (150 K) crystal structure of II was determined by X-ray diffraction methods. The substance crystallizes in the monoclinic space group P21/n with a = 4.088(1) Å, b = 22.346(1) Å, c = 8.284(1) Å, b = 100.687(3) and Z = 4 molecules per unit cell. The conformation adopted by the thiocarbamate group –OC(S)N(H)– is syn (C=S double bond in synperiplanar orientation with respect to the N–H single bond), while the methoxycarbonyl C=O double bond is in antiperiplanar orientation with respect to the N–H bond. The non-H atoms in II are essentially coplanar and the molecules are arranged in the crystal lattice as centro-symmetric dimeric units held by  N-H...S=C hydrogen bonds [d(NS) = 3.387(1) Å, angle(N-H..S) = 166.4(2)º]. Furthermore, the effect of the p electronic resonance in the structural and vibrational properties is also discussed.