Synthesis of 2-(5-bromo-2-(2,2,2-trifluoroethoxy)phenyl)-5-aryl-1,3,4-oxadiazoles and their FT-IR, NMR, Mulliken, MEP, HOMO-LUMO and NLO

Available online at www.worldscientificnews.com WSN 97 (2018) 80-98 EISSN 2392-2192 Synthesis of 2-(5-bromo-2-(2,2,2-trifluoroethoxy) phenyl)-5-aryl-1,3,4-oxadiazoles and their FT-IR, NMR, Mulliken, MEP, HOMO-LUMO and NLO C. Rajalakshmi and N. Santhi* Department of Chemistry, Government Arts College, Chidambaram – 608201, Tamil Nadu, India *E-mail address: ABSTRACT A series of novel 2-(5-bromo-2-(2,2,2-trifluoroethoxy)phenyl)-5-aryl-1,3,4-oxadiazole (3a-e) were synthesized and confirmed by spectral analyses. The optimized structure with their bonding aspects and vibrational frequencies of the same have been examined utilizing DFT-B3LYP technique with a basis set 6-31G(d,p). In the optimized structures of compounds 3a-e, the bond lengths and bond angles are in accord with their corresponding reported analogous. The vibrational frequencies resulted from experimental as well as theoretical are in well accord with each other. Furthermore, Mulliken charge and MEP analyses of the compound have been calculated in order to get insight into the compound. The quantum chemical descriptors such as HOMO and LUMO energies were used to analyze the charge transfer within the molecule. In addition, the results of polarizabilities, first order hyperpolarizabilities and dipole moment of title compounds imply that these could be utilized for the preparation of NLO crystals. Keywords: 1,3,4-oxadiazoles, FT-IR, hyperpolarizability, HOMO –LUMO 1. INTRODUCTION Oxadiazoles are among the most prevalent heterocycles in biologically active compounds. Of course, numerous oxadiazoles derivatives possess potent biological activities including ntiinflammatory [1-4], hypoglycemic [5,6], antianxiety, antidepressant [7], and ( Received 24 March 2018; Accepted 08 April 2018; Date of Publication 09 April 2018 ) World Scientific News 97 (2018) 80-98 antimitotic [8] activities. In addition to these, a number of researchers have reported antimicrobial activities [9-13]. A minority example of oxadiazole-based compounds have been recently used as electron transport materials [14-19] in organic light emitting diodes (OLEDs) Nowadays, the recognition and discovery of environmentally and biologically important analytes has become an essential research topic in chemistry and biology. Among different analytical methods, optical measurements in conjunction with suitable biological activity are preferable approaches for detection, because they are convenient, low cost, nondestructive, and highly sensitive and selective to analytes. The importance of the oxadiazoles functionality in biologically active compounds has fused research into the development of new protocols for the synthesis and study of their molecular structural properties, electronic and polarizability data of oxadiazoles, in gas phase, due to its pharmaceutical importance. A series of derivatives of oxadiazoles were synthesized and tested, revealing precise requirements for activity in tight and relatively level molecular structural properties, electronic and polarizability. The unaltered 5-bromo-2-(2,2,2-trifluoroethoxy)phenyl core was shown to be optimal for activity while certain modifications to the phenyl ring were tolerated. The ground state properties of the modified molecules are calculated using DFT/B3LYP level of theory using 6-31G(d,p) basis set. We therefore wished to investigate and examine their molecular structure, FT-IR, dipole moment, polarizability, first order hyperpolarizability, HOMO– LUMO, Mulliken population analysis along with the molecular electrostatic potential surface. 2. EXPERIMENTAL 2. 1. General Procedure for the Synthesis of 2-(5-bromo-2-(2,2,2-trifluoroethoxy) phenyl)-5-aryl-1,3,4-oxadiazole (3a-e) In a round bottom flask, aryl hydrazide 1(a-e) was dissolved in phosphorous oxychloride (5 mL) and to it equimolar amount of 5-bromo-2-(2,2,2-trifluoroethoxy)benzoic acid 2 was added. This mixture was refluxed at mild condition. After completion of the reaction, the mixture was cooled to room temperature and poured onto crushed ice. On neutralization of the contents with sodium bicarbonate solution (20%), a solid mass separated out. This was filtered and washed with water. It was crystallized by using methanol to give 3a-e. The synthetic route is given Scheme 1. Scheme 1. -81- World Scientific News 97 (2018) 80-98 2. 2. Spectral measurements The FT-IR spectrum of the synthesized compounds was measured in the range 4000500 cm-1 on a AVATAR-330 FT-IR spectrometer (Thermo Nicolet) using KBr (pellet form). 1 H NMR spectrum was recorded at 400 MHz on a BRUKER and for 13C NMR spectrum was recorded at 100 MHz on a BRUKER model using CDCl3 as solvent. Tetramethylsilane (TMS) was used as internal reference for all NMR spectra, with chemical shifts reported in δ units (parts per million) relative to the standard. 2-(5-bromo-2-(2,2,2-trifluoroethoxy)phenyl)-5-phenyl-1,3,4-oxadiazole (3a). Yield 76%, white powder, mp (°C): 240-242; IR (cm−1): 3072 (νArC-H), 2922 (νAli.C-H), 1587 (νC=N), 1063 (νC–O–C), 1271 (νC-F), 1275-1245 (βC-H), 1063-818; 1H NMR (CDCl3, 400 MHz, ppm): 4.77 (s, 2H), 6.94-8.16 (m, 2H, Ar-H); 13C NMR (CDCl3); 154.5 (C-5), 165.3 (C-9), 161.7 (C-12), 67.7 (C-15). 2-(5-bromo-2-(2,2,2-trifluoroethoxy)phenyl)-5-(4-chlorophenyl)-1,3,4-oxadiazole (3b). Yield 75%, white powder, mp (°C): 240–242; IR (cm−1): 3076 (νArC-H), 2946 (νAli.C-H), 1575 (νC=N), 1059 (νC–O–C), 1277 (νC-F), 12491179 (βC-H), 1059-796; 1H NMR (CDCl3, 400 MHz, ppm): 4.53 (s, 2H), 6.93-8.34 (m, 2H, Ar-H); 13C NMR (CDCl3); 154.0 (C-5), 164.5 (C-9), 163.9 (C-12), 67.5 (C-15). 2-(5-bromo-2-(2,2,2-trifluoroethoxy)phenyl)-5-(4-nitrophenyl)-1,3,4-oxadiazole (3c). Yield 75%, white powder, mp (°C): 240–242; IR (cm−1): 3099 (νArC-H), 2954 (νAli.C-H), 1584 (νC=N), 1066 (νC–O–C), 1291 (νC-F), 1291,1267 (βC-H), 1107-739; 1H NMR (CDCl3, 400 MHz, ppm): 4.54 (s, 2H), 6.94-8.43 (m, 2H, Ar-H); 13C NMR (CDCl3); 154.5 (C-5), 163.6 (C-9), 161.7 (C-12), 67.5 (C-15). 2-(5-bromo-2-(2,2,2-trifluoroethoxy)phenyl)-5-(3-bromophenyl)-1,3,4-oxadiazole (3d). Yield 78%, white powder, mp (°C): 240–242; IR (cm−1): 3071 (νArC-H), 2922 (νAliC-H), 1604 (νC=N), 1063 (νC–O–C), 1292 (νC-F), 1267,1246 (βC-H), 1071-815; 1H NMR (CDCl3, 400 MHz, ppm): 4.51 (s, 2H), 6.93-8.33 (m, 2H, Ar-H); 13C NMR (CDCl3); 154.5 (C-5), 164.0 (C-9), 162.0 (C-12), 67.1 (C-15). 2-(5-bromo-2-(2,2,2-trifluoroethoxy)phenyl)-5-(pyridin-4-yl)-1,3,4-oxadiazole (3e). Yield 68%, white powder, mp (°C): 240–242; IR (cm−1): 3098 (νArC-H), 2922 (νAli.C-H), 1595 (νC=N), 1059 (νC–O–C), 1295 (νC-F), 1269,1247 (βC-H), 1058-818; 1H NMR (CDCl3, 400 MHz, ppm): 4.50 (s, 2H), 6.87-8.76 (m, 2H, Ar-H); 13C NMR (CDCl3); 151.4 (C-5), 164.8 (C-9), 159.1 (C-12), 57.6 (C-15). 2. 3. Computational studies GAUSSIAN 03W [20] software package was used for DFT calculations. Structure optimizations of 3a-e were performed at the Density Functional Theory (DFT) level employing B3LYP/6-31G(d,p) functional theory. In addition, virational analysis (...truncated)