A theoretical study an influence of oxygen group elements to rotational barrier of 2-(2'-pyridyl)-1,3,4-oxa(thia, selena and tellura) diazoles

Abstract

Surveying of the refernces shows that selenium and tellurium containing compounds will be one of the most promising heterocycles in the future. Therefore, the influence of oxygen group elements – O, S, Se and Te to rotational barrier heights of 2-(2’-pyridyl)-1,3,4-oxa (thia, selena and tellura) diazoles were investigated by DFT/def2-TZVP method and also by DFT/6-311G(d) method only for O, S and Se series. And also, their thermodynamic parameters (∆H,∆G) were calculated in gas phase. Furthermore, some model compounds with conjugated C=C-C=C, N=C-C=C and N=C-C=N fragments with neighbouring chalcogen atoms were considered. It was found that, a rising of barrier heights in the case of 2-(2’-pyridyl)-1,3,4-oxa(thia, selena and tellura)diazoles and also, in the model compounds with N=C-C=N fragment by increasing atomic number of chalcogen atom. By going from O to Te the rising of HOMO level and decreasing of HOMO-LUMO energetic gap were observed. It was found that, turning of pyridyl ring to ±30◦ from the coplanar cis (cyn) structure due to the lone pair electron repulsion of nitrogen atoms of N=C-C=N fragment in the case of S, Se and Te containing considered compounds. This is also leads to stability of the trans (anti) structure relatively to cis (cyn) structure and the trans-cis energy difference is increasing by going O to Te. And also, the trans structure is becoming more stable due to the hydrogen bond between nitrogen atom of chalcogenazole ring and H atom of pyridine ring in orto position.