Configuration of the S-alkyl thiohydroximates: crystal and molecular structures of syn-(alkylthio)-isomers of S-methyl and S-cyanoethyl O-(N-methylcarbamoyl)acetothiohydroximates

Abstract

Crystal-structure determinations of the α-isomers of S-methyl and S-cyanoethyl O-(N-methylcarbamoyl)acetothiohydroximates have confirmed the syn-(alkylthio)-configuration of the thermodynamically stable α-form of the S-alkyl thiohydroximates. The S-methyl compound crystallizes in the monoclinic space group P2₁/n, with a= 6·07, b= 9·64, c= 13·95 Å, β= 91° 30′, and Z= 4. The S-cyanoethyl compound crystallizes in the orthorhombic space group Pca2₁, with a= 12·67, b= 4·91, c= 16·25 Å, and Z= 4. The X-ray intensities were recorded photographically (Cu-K_α radiation) and measured by an integrating microdensitometer. The atomic co-ordinates and vibration parameters were obtained by Fourier and least-squares calculations to give R 0·080 over 898 reflections for the S-methyl compound and 0·081 over 868 reflections for the S-cyanoethyl compound. The CN and N–O bonds of the substituted oximes have mean lengths of 1·282 and 1·446 Å, respectively, and the latter value is significantly longer than the distance of ca. 1·40 Å in free oximes. The C–N–O and N–O–C valency angles have mean values of 109·9 and 112·4°. The S–C(sp³) and S–C(sp²) bonds have mean lengths of 1·811 and 1·750 Å, respectively.