Synthesis and Structures of 5-(2,4-Dichlorophenyl)-1,3,4-Oxadiazole-2-Thione Alkyl Derivatives and Estimation of the Aromaticity of the Oxadiazole Ring

A series of 5-(2,4-dichlorophenyl)-1,3,4-oxadiazole-2-thione alkyl derivatives are obtained. Structures of the products are determined from the IR, UV, ¹H and ¹³C NMR spectroscopic results together with single crystal X-ray diffraction (XRD). The aromaticity of the 1,3,4-oxadiazole ring is estimated by single crystal XRD and DFT calculations using the Multiwfn program package. It is found that in S-derivatives, the π electron system is redistributed in the pseudo-aromatic 1,3,4-oxadiazole-2-thione moiety relative to initial 5-(2,4-dichlorophenyl)-1,3,4-oxadiazole-2(3H)-thione. In the S-derivatives of 5-(2,4-dichlorophenyl)-1,3,4-oxadiazole-2-thione the aromaticity of the 1,3,4-oxadiazole heterocycle is lower than that in N3-derivatives.