N–H⋯SC hydrogen bond in O-alkyl N-methoxycarbonyl thiocarbamates, ROC(S)N(H)C(O)OCH3 (R = CH3–, CH3CH2–)

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, β = 100.687(3)° and Z = 4 molecules per unit cell. The conformation adopted by the thiocarbamate group –OC(S)N(H)– is syn (CS double bond in synperiplanar orientation with respect to the N–H single bond), while the methoxycarbonyl CO 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···SC hydrogen bonds [d(N···S) = 3.387(1) Å, ∠(N−H···S) = 166.4(2)°]. Furthermore, the effect of the π electronic resonance in the structural and vibrational properties is also discussed.

Graphical abstractThe synthesis and full characterization of two O-alkyl N-methoxycarbonyl thiocarbamates, ROC(S)N(H)C(O)OCH3 (R = CH3–, CH3CH2–), are reported. The structure and conformation are studied by using a combined experimental (X-ray, IR and Raman spectroscopy) and theoretical approach. The crystal structure of CH3CH2OC(S)N(H)C(O)OCH3 shows the presence of centro-symmetric dimeric units held by N−H⋯SC hydrogen bonds. The conjugative (resonance) effect in the thiocabamate group –OC(S)N(H)– is discussed.Figure optionsDownload full-size imageDownload as PowerPoint slide