ORIGINAL RESEARCH Effects of different GIAO and CSGT models and basis sets on 2-aryl-1,3,4-oxadiazole derivatives Davut Avcı Æ Yusuf Atalay Received: 2 July 2008 / Accepted: 17 December 2008 / Published online: 7 January 2009 Ó Springer Science+Business Media, LLC 2009 Abstract The direct molecular structure implementations of the gage-including atomic orbital (GIAO), individual gages for atoms in molecules (IGAIM) and continuous set of gage transformations (CSGT) methods for calculating nuclear magnetic shielding tensors at both the Hartree-Fock (HF) and density functional (B3LYP) levels of theory with 6-31G(d), 6-311G(d), 6-31??G(d,p), 6-311??G(d,p), and 6-311??G(df,pd) basis sets are presented. Dependence on the 1 H and 13 C NMR chemical shifts on the choice of method and basis set have been investigated. Also, these chemical shifts of 2-aryl-1,3,4-oxadiazoles 5a–g have been performed related to dihedral angles (C4–C3–C2–O) of two conformers. The optimized molecular geometries and 1 H and 13 C chemical shift values of 2-aryl-1,3,4-oxadiazoles 5a–g in the ground state have been obtained. The linear correlation coefficients of 13 C NMR chemical shifts for these molecules were given. The new nuclear magnetic shielding tensors of tetramethylsilane (TMS) were calcu- lated. The data of 2-aryl-1,3,4-oxadiazole derivatives display significant molecular structure and NMR analysis. Also, these provide the basis for future design of efficient materials having the 1,3,4-oxadiazole core. Keywords DFT Á HF Á GIAO Á CSGT Á 1 H Á 13 C NMR Á TMS Á 2-aryl-1,3,4-oxadiazoles Á Structure-correlation analysis Introduction 1,3,4-Oxadiazoles are very interesting in medicinal chem- istry. Besides, derivatives of 1,3,4-oxadiazoles have been reported to exhibit diverse biological activities. It is fre- quently used in pharmaceutical industry [1–6]. Various oxadiazole-containing molecular structures were synthe- sized [7–13]. Furthermore, the 1,3,4-oxadiazole ring which is a new NLO motifs among the heterocyclic compounds were used as a p-bridge on the ground. Its reduced aromaticity may offer better prospects for p-electron delocalization across the D–A links [13]. However, typical electron-transporting materials usually contain a p-electron deficient heterocyclic moiety, such as oxadiazoles, tria- zoles, triazines, etc., which can effectively improve the electron affinity [14]. Experimental measurements and theoretical calculations on NMR chemical shift become one of the key factors in the molecular structure correlations design. Theoretical determination of NMR chemical shift is quite useful both for understanding the relationship between the molecular structure and electronic properties of molecules. It also provides a guideline to experimentalists for the design and synthesis of organic materials [6]. The aim of the present work is to describe and charac- terize the relation between the molecular structure and chemical shifts correlations of 2-aryl-1,3,4-oxadiazoles 5a–g. A number of papers have recently appeared in the literature concerning the calculation of NMR chemical shift (c.s.) by quantum-chemistry methods [15–20]. These papers indicate that geometry optimization is a crucial factor in an accurate determination of computed NMR chemical shift. Moreover, it is known that the density functional theory (DFT) (B3LYP) method adequately takes into account electron-correlation contributions, which are D. Avcı Á Y. Atalay (&) Faculty of Arts and Sciences, Department of Physics, Sakarya University, 54100 Sakarya, Turkey e-mail: yatalay@sakarya.edu.tr 123 Struct Chem (2009) 20:185–201 DOI 10.1007/s11224-008-9400-1