Synthesis, Characterization and DFT studies of 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole

 

S. Sangeetha^1*, T.F.Abbs Fen Reji²

¹Department of Chemistry, Sivanthi Adithanar College, Pillayarpuram-629501, Tamilnadu, India

²Department of Chemistry and Research Centre, Nesamony Memorial Christian College, Marthandam-629165, Tamilnadu, India

 

ABSTRACT:

In this work the vibrational spectral analysis was carried out by using infrared spectroscopy for 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole molecule. The molecule structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations based on density functional theory method and different basis sets combination. The calculated HOMO and LUMO energies show the chemical activity of the molecule, and this energy gap is an important value for stability index. The Mulliken changes, the values of electric dipole moment of the molecule were computed using DFT calculations obtained from Gaussian 09 software. We conclude that the observed and the calculated frequencies are found to be in good agreement.

 

 

 

INTRODUCTION:

The thiazole ring system is probably the most important heterocyclic in nature¹ owing to the great structural diversity of biologically active thiazoles. The syntheses of various heterocyclic compounds are known for their anti-infective, especially antibacterial and antifungal activities². The biological importance of thiazole derivatives was emphasized during the period 1941-1945.When research on the structure of the antibiotic penicillin showed the presence of a thiazolidine ring in an important therapeutic agent³. 2-Aminothiazole forms an important class of chemical sciences which involved in numerous applications including human and veterinary medicine⁴.

 

 

 

The 2-Aminobenzothiazole molecule is known for its local anesthetic action and has numerous applications in human and veterinary medicine. Several substituted benzimidazoles and benzothiazoles⁵ have been identified as potent authelmintic drugs. Benzothiazoles constitute an important class of compounds with interest to medicinal chemists as compounds bearing the benzothiazolyl moiety.

 

Urea is the first organic compound that was synthesized in lab in 1928, which become the important synthesis step in the history of synthetically organic chemistry and played important physiological and biological roles in animal kingdom^6-8. Thiourea is the analogue compound to urea with Replacement of oxygen atom in urea by sulphur atom, also thiourea have a considerably wide range of applications. The properties of urea and thiourea differ significantly because of the difference in electro negativity between sulfur and oxygen⁹. Thiourea compounds works as building blocks in the synthesis of heterocyclic compounds¹⁰. Substituted thioureas have recently gained much interest in the preparation of wide variety of biologically active compounds^{11, 12}. Thioureas are important organic compounds posses’ high biological activity, act as corrosion inhibitors and antioxidant and are polymer components¹³. Thiourea and urea derivatives show a broad spectrum of biological activities as anti - HIV, antiviral, HDL – elevating, antibacterial and analgesic properties^14-17. Acylthiourea derivatives are well known for wide range of biological activities like bactericidal, fungicidal, herbicidal, insecticidal action and regulating activity for plant growth^{18, 19}.

 

Plentiful computational methods have been accomplished to correlate the electronic structure and chemical reactivity. Conceptual DFT has been favorably used to unfold chemical reactivity and site selectivity. In order to analyse the chemical reactivity various global and local quantities were utilized. Vibrational spectroscopy is used to identify functional groups and determine the molecular structure of crystals. It also characterizes the bioactivity of the material. Density functional theory (DFT) method is used for the computation of molecular structure, vibrational wave numbers and energies of chemical reactions.

 

Literature survey by us reveals that no experimental and computational vibrational spectroscopic study on 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole is published yet. This inadequacy observed in the literature encouraged us to be making this theoretical and experimental vibrational spectroscopic research based on the molecule to give a correct assignment of the fundamental FT-IR spectra. Therefore the present study aims to give a complete description of the molecular geometry and molecular vibrational assignment of 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole.

 

The optimized geometry of the vibrational frequencies was calculated at DFT/B3LYP level of theory using the 6-31G basis set²⁰. These methods predict relatively accurate molecular structure and vibrational spectra with moderate computational effort. In DFT methods Becke’s three parameter exact exchange - functional (B3)²¹ combined with gradient – corrected correlation functional of Lee, Yang and Parr  (LYP)^{22, 23} and Perdew and Wang (PW91) are the best predicting results^{24, 25}  for molecular geometry and  vibrational wave numbers for moderately larger molecule^26-28 and the Barone and Adamo’s Becke- style one – parameter functional using the  modified Perdaw – Wang exchange and Perdew – Wang 91 correction method (MPWIPW91) are the best predicting results for molecular geometry and vibrational wave numbers for moderately larger molecule^29-31.

 

EXPERIMENTAL:

The reagents and solvents used were of AR grade. All the chemicals were purchased from Sigma – Aldrich, Merck specialties Pvt. Ltd. and Himedia Laboratories Pvt. Ltd. The compound 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole was prepared according to the following method. A solution of 1-aryl-3-(N,N-dimethylimdoyl) thiourea (1m mol) in DMF (2 ml) was added to a solution of 2-(2-bromoactyl)-N-methyl-6-chlorobenzimidazole (0.254g, 1mmol) which was prepared from 2-(1-hydroxy ethyl)-6-chlorobenzimidazole in DMF (2ml). The reaction mixture was stirred well and triethylamine (0.15ml, 1mmol) was added. The reaction mixture was heated at 80-85 C for 5 minutes. It was then cooled and poured   in to ice - cold water with constant stirring. The yellow precipitate thus obtained was filtered, washed with water and dried. The crude product was crystallized from ethanol - water (2:1) to give yellow crystalline solid.

 

Computational Method:

Geometry optimization is one of the most important steps in theoretical calculations. The molecular structure of the title compound in the ground state is computed by performing by DFT with 6-31G/basis set. The optimized structural parameters are used in the vibrational frequency calculations at DFT levels. At the optimized geometry for the title molecule no imaginary frequency modes were obtained, so there is a true minimum on the potential energy surface was found. The DFT hybrid B3LYP functional tends also to overestimate the fundamental modes. Therefore scaling factors have to be used for obtaining a considerably better agreement with experimental data. Therefore a scaling factor of 0.962 was uniformly applied to the DFT calculated wave numbers³². The assignment of the calculated wave numbers is aided by the animation option of Gauss view program, which gives a visual presentation of the vibrational modes³³.

 

RESULTS AND DISCUSSION:

Optimized geometry:

The optimized geometry of 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole was obtained at B3LYP level. The molecular structure along with the numbering of atoms is shown in Fig.1.The theoretical and experimental values were compared and small deviations in some values were observed. There are changes observed in C-H bond length due to variation in the charge distribution on the carbon atom of the benzene ring. The comparative optimized structural parameters such as bond lengths, bond angles and dihedral angles are presented in Table 1, 2 and 3. The molecule contains benzimidazole ring, phenyl ring, amino group, methyl group and chlorine atom. The optimized bond length of C-C in phenyl ring fall in the range from 1.3776 Å to 1.4786 Å. The optimized bond length of C-H in methyl group is 1.0830 Å. The title compound has one C-O bond and its optimized bond length is 1.2637 Å, nine C-N bonds and its optimized bond length ranges from 1.3333 Å to 1.4752 Å, two C-S bonds and its bond length ranges from 1.8382 Å to 2.8012 Å, one N-H bond and its optimized bond length is 1.0105 Å, eleven C-C bond and its optimized bond length ranges from 1.3871 Å to 2.5130 Å, twelve C-H bonds and its optimized bond length ranges from 1.0791 Å to 1.0830 Å, one C-Cl bond and its optimized bond length value is 1.8329 Å.

 

 

Figure 1: Optimized geometrical structure of 2-(2-phenylaminothiazol-5-oyl)-1-methyl-6- chlorobenzimidazole.

 

Table 1: Optimized geometrical parameters of 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole.

Bond length data of 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole

Bond	Bond Length (Å)
N1-C2	1.3333
C2-N3	1.4008
N3-C4	2.5953
C4-C5	1.3872
C5-C6	1.4142
C6-C7	1.3871
N3-C8	1.3939
N1-C9	1.384
C2-C10	1.4786
C10-S11	2.8012
S11-C12	1.8382
C12-N13	1.3233
N13-C14	1.3757
C14-C15	1.3776
C12-C16	2.513
C16-C17	1.4079
C17-C18	1.3945
C18-C19	1.4004
C19-C20	1.399
C20-C21	1.3986
C12-C22	1.3582
C10-O23	1.2637
C5-H24	1.083
C6-H25	1.084
C7-H26	1.0832
N22-H27	1.0105
C21-H28	1.0804
C17-H29	1.0874
C20-H30	1.0853
C18-H31	1.0851
C19-H32	1.0847
N3-C33	1.4752
C33-H34	1.09
C33-H35	1.0899
C33-H36	1.0847
C14-H37	1.0791
C4-Cl38	1.8329

 

Table2: Bond Angle data of 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole

Bond	Bond Angle (Å)
N1-C2-N3	112.34
C2-N3-C4	128.36
N3-C4-C5	141.4
C4-C5-C6	121.27
C5-C6-C7	120.79
C2-N3-C8	106.3
C2-N1-C9	106.15
N1-C2-C10	124.37
C2-C10-S11	155.18
C10-S11-C12	113.71
S11-C12-N13	114.54
C12-N13-C14	112.12
N13-C14-C15	117.51
S11-C12-C16	144.95
C12-C16-C17	141.27
C16-C17-C18	120.22
C17-C18-C19	120.21
C18-C19-C20	119.31
C19-C20-C21	121.24
S11-C12-N22	119.12
C2-C10-O23	120.05
C4-C5-H24	118.85
C5-C6-H25	118.78
C6-C7-H26	122.25
C12-N22-H27	115.84
C20-C21-H28	121.44
C16-C17-H29	119.84
C19-C20-H30	119.91
C17-C18-H31	119.48
C18-C19-H32	120.27
C2-N3-C33	126.08
N3-C33-H34	109.97
N3-C33-H35	109.97
N3-C33-H36	108.74
N13-C14-H37	119.9
N3-C4-Cl38	101.79

 

 

 

Table 3: Dihedral Angle data of 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole

Bond	Dihedral Angle  (Å)
N1-C2-N3-C4	0.00
C2-N3-C4-C5	0.00
N3-C4-C5-C6	0.00
C4-C5-C6-C7	0.00
N1-C2-N3-C8	0.00
N3-C2-N1-C9	0.00
C9-N1-C2-C10	179.99
N1-C2-C10-S11	0.01
C2-C10-S11-C12	0.00
C10-S11-C12-N13	0.00
S11-C12-N13-C14	0.00
C12-N13-C14-C15	0.00
C10-S11-C12-C16	-179.99
S11-C12-C16-C17	0.00
C12-C16-C17-C18	179.99
C16-C17-C18-C19	0.00
C17-C18-C19-C20	0.00
C18-C19-C20-C21	0.00
C10-S11-C12-N22	-179.99
N1-C2-C10-O23	-179.99
N3-C4-C5-H24	179.99
C4-C5-C6-H25	-180.00
C5-C6-C7-H26	179.99
S11-C12-N22-H27	0.00
C19-C20-C21-H28	-179.90
C12-C16-C17-H29	0.00
C18-C19-C20-H30	-180.00
C16-C17-C18-H31	-180.00
C17-C18-C19-H32	180.00
N1-C2-N3-C33	-179.99
C2-N3-C33-H34	-59.40
C2-N3-C33-H35	59.25
C2-N3-C33-H36	179.92
C12-N13-C14-H37	-179.92
C2-N3-C4-Cl38	179.99

Table 4: IR Absorption Frequency of 2-(2-phenylaminothiazol-5-oyl)-1-methyl-6- chlorobenzimidazole.

Mode	Exp. IR frequency (cm-1)	Frequency   (unscaled) (cm-1)	Frequency (scaled) (cm-1)	Intensity	Vibrational Assignments
108	3447	3620.26	3482.69	70.5761	N22-H27 (asym.str.)
107	3167	3298.44	3173.09	8.2597	C14-H37 (asym.str.)
106		3270.72	3146.43	12.58	C21-H28 (asym.str.)
105		3246.64	3123.26	9.5968	C7-H26, C6-H25, C5-H24 (asym.str.)
104		3243.3	3120.05	3.6493	C33-H36, C33-H35 (asym.str.)
103		3238.71	3115.63	1.9681	C7-H26, C5-H24 (asym.str.)
102		3227.66	3105	35.531	C18-H31, C19-H32, C20-H30 (asym.str.)
101		3218.34	3096.04	7.1482	C5-H25, C7-H26 (asym.str.)
100		3211.02	3089	27.38	C18-H31, C20-H30 (asym.str.)
99		3200.1	3078.49	0.0133	C17-H29, C18-H31, C19-H32 (asym.str.)
98		3182.6	3061.66	6.764	H35-C33-H34 (asym.str.)
97		3178.65	3057.86	13.6417	C17-H29, C18-H31 (asym.str.)
96		3110.56	2992.35	14.2822	C33-H34-H35-H36 (asym.str.)
95	1604	1673.86	1610.25	1.3805	C7-H26, C6-H25, C5-H24 (bend)
94		1665.14	1601.86	32.9229	N22-H27, phenyl ring bend (ip)
93		1661.51	1598.37	105.4042	N22-H27, phenyl ring bend (ip)
92		1620.15	1558.5	117.8383	C10-O23 bend (twist.), N22-C12 (sym.str.)
91	1580	1611.9	1550.64	39.5401	Benzimidazole ring puckering
90		1601.06	1540.21	542.2646	N22-H27, C19-H32, C20-H30, C18-H31 (bend)
89		1581.62	1521.51	296.3831	C12-N22-H27 bend (rock.), C10-O23 (bend) CH3 gp. vib.Vib.
88		1553.42	1494.39	137.7437	Phenyl ring vib.
87	1486	1548.01	1489.18	2.601	Benzimidazole ring vib.
86		1540.39	1481.85	585.63	C5-H24, C6-h25, C7-H26, C8-N3 bend (twist.), CH3gp.bend (rock.)
85		1533.46	1475.18	14.563	CH3gp.bend (rock.)
84		1533.14	1474.88	665.12	CH3 gp.bend (rock.), C14-H37, C14-C15, N22-H27, N1-C2 bend (rock.)
83		1522	1464.16	28.208	CH3 gp. bend (twist.)
82		1515.08	1457.5	377.8975	C12-N22-H27 bend (wagg.), CH3 gp. bend (twist.), benzimidazole ring vib.
81	1418	1504.19	1447.03	22.7174	Phenyl ring vib. C19-H32, C18-H31, C20-H30 bend (wagg.)
80		1447.58	1392.57	44.8678	C2-N1 bend (twist.), C5-H24, C7-H26, C6-H25 bend (wagg.)
79		1412.54	1358.86	32.8842	O23-C10, N1-C2, bend (twist.), CH3 gp. bend (wagg.)
78		1397.54	1344.43	6.3171	Phenyl ring bend (wagg.)
77		1393.99	1341.01	245.5807	Benzimidazole ring and phenyl ring vib.
76	1317	1373.97	1321.75	9.6345	Phenyl ring puckering
75		1346.93	1295.74	11.6615	Benzimidazole vib., C14-H37, bend (ip),  CH3 gp. vib.
74		1325.7	1275.32	7.7439	C14-H37, C5-H24, C6-H25, C7-H26 bend (wagg.), C14-N13 bend (rock.), C10-O23 bend (ip)
73		1314.92	1264.95	1.0659	C9-N1 bend (twist.), C6-H25 bend (ip), CH3gp. bend (op),  phenyl ring vib.
72		1301.83	1252.36	56.8373	Phenyl ring vib., C14-H37 bend (wagg.), N22-H27 bend (twist)
71	1243	1288.74	1239.76	131.1293	C10-O23 bend (wagg.), H37-C14-C15 bend (rock.)  Phenyl ring and CH3 gp.vib.
70		1260.46	1212.56	44.3614	Benzimidazole ring and phenyl ring puckering, H37-C14 bend (twist.) C5-H24, C6-H25, C7-H26 bend (wagg.)
69		1246.68	1199.3	487.6537	N13-C12, C14-N13-H37 bend (rock.), phenyl ring vib,
68		1239.53	1192.42	39.7099	Phenyl ring bend (op)
67		1223.77	1177.26	2.844	C19-H32, C1-H31, C20-H30 bend (rock.)
66		1185.78	1140.72	67.139	Benzimidazole ring vib., C7-H26, C5-H25 bend (wagg.)
65		1174.55	1129.91	0.134	CH3 gp. bend (op)
64	1104	1157.52	1113.53	61.3746	CH3 gp. bend (op), C10-O23 bend (twist.), N1-C2 bend (op), C15-C14-H37 bennd (sciss.)
63		1133.32	1090.25	19.1512	Phenyl ring puckering, C12-N22-H27 bend (sciss.)
62	1081	1128.14	1085.27	7.6081	N22-H27 bend (twist.), C20-H30, C19-H32, C17-H29 bend (wagg.)
61		1122.31	1079.66	84.8253	CH3 gp. bend (op), N22-H27 bend (op), C7-H26 bend (wagg.)
61		1122.31	1079.66	84.8253	CH3 gp. bend (op), N22-H27 bend (op), C7-H26 bend (wagg.)
60		1091.34	1049.86	6.1276	C5-H24, C7-H26 bend (rock.)
59		1067.64	1027.06	3.9386	Phenyl gp. bend (twist.)
58		1039.58	1000	2.899	C21-H28, C20-H30, C19H32 bend (op)
57		1034.1	994.8	0.6741	Phenyl ring puckering,
56		1010.78	972.37	1.0105	C7-H26, C6-H25, C5-H24 bend (op)
55		1001.78	963.71	0.3754	C17-H29, C18-H31, C19-H32, C20-H30 bend (op)
54		977.29	940.152	6.5553	C14-H37 bend (op)
53		957.46	921.07	109.158	Benzimidazole ring puckering
52		948.26	912.22	12.8478	C17-H29, C18-H31, C19-H32, C20-H30 bend (op), C21-H28 bend (rock.)
51		940.25	904.52	0.0157	C7-H26, C5-H24, C6-H25 bend (sciss.)
50	892	921.29	886.28	61.7738	Benzimidazole ring puckering, CH3 gp. vib., C10-O23 bend (twist.)
49	858	870.75	837.66	0.5441	C21-H28, C20-H30, C19-H32, C18-H31, C17-H29 bend (wagg.)
48		860.34	827.64	6.7541	Benzimidazole ring puckering, CH3 gp. vib., C10-O23 bend (twist.)
47		842.9	810.86	0.1656	Phenyl ring puckering, N22-H27 bend (rock.)
46		827.14	795.7	30.7954	Benzimidazole ring bend (op)
45		821.96	790.72	56.7525	C12-S11 (sym.str.), C10-O23 bend (op)
44		806.39	775.74	0.0482	C10-O23 bend (rock.), C14-C15 bend (op)
43		794.94	764.73	91.6927	C20-H30, C19-H32, C18-H31 bend (wagg.)
42	757	770.43	741.15	33.1973	Benzimidazole ring vib.
41		767.59	738.42	10.4556	Benzimidazole ring puckering
40	693	721.24	693.83	24.3597	Phenyl ring vib.
39		707.87	680.95	11.7708	C15-S11 (sym,str.), phenyl ring and benzimidazole ring puckering
38		672.11	646.56	8.7775	C33-H35-H34 bend (rock.)
37		666.51	641.18	4.6132	Benzimodazole ring and phenyl ring puckering, C10-O23 bend (sciss.), C12-S11-C15 bend (twist.)
36		661.06	635.93	71.5472	N22-H27 bend (op)
35		649.44	624.76	1.6024	Phenyl ring puckering
34		623.46	599.76	6.303	N22-H27 bend (rock.)
33		616.26	592.84	10.3143	C10-O23 bend (twist.), benzimidazole ring, thiazole ring,phenyl ring puckering
32		603.38	580.45	41.5755	CH3 gp.bend (op), C15-S11 (sym.str.)benzimidazole ring vib.
31		595.33	572.7	0.0956	C33-H34-H35 bend (rock.),C5-H24,C6-H25 bend (sciss.)
30		589.78	567.36	21.9232	Benzimidazole ring puckering, C15-S11 bend (wagg.), C10-O23 bend(twist.)
29		588.04	565.69	5.36	CH3 gp. bend (op), C12-S11 bend (twist.), phenyl ring and benzimidazole ring puckering
28		546.09	525.33	4.7182	C7-H26, C6-H25 bend (sciss.)
27		528.55	508.46	24.5498	N22-H27, C14-H47 bend (twist.), C18-H31, C19-H32, C20-H30 bend (rock.)
26		506.68	487.42	4.6024	N22-H27, C14-H47 bend (twist.), C18-H31, C19-H32, C20-H30 bend (rock.)
25		493.84	475.07	0.0257	C12-S11-C15 bend (rock.), C10-O23 bend (sciss.), CH3 gp. bend (op), thiazole ring puckering
24		428.77	412.47	0.0036	C21-H28, C20-H30, C19-H32, C18-H31, C17-H29 bend (wagg.)
23		390.04	375.21	5.3664	C4-Cl38 bend (op), CH3gp. bend (op), C10-O23 bend (rock.),benzimidazole ring puckering
22		384.62	369.6	13.4807	CH3gp. bend (op), C10-O23 bend (rock.),benzimidazole ring puckering
21		342.82	329.79	1.9541	CH3gp. bend (op), C8-C4 bend (twist.)
20		333.41	320.74	0.2444	CH3gp.vib., C6-H25, C7-H26, C5-H24 bend(wagg.)
19		322.4	319.76	1.8543	C4-Cl38 bend (twist.),C10-O23 bend (rock.), phenyl ring and benzimidazole ring puckering
18		315.62	303.62	2.6226	N22-H27, C2-N1, H24-C5, H25-C6, H26-C7 bend (wagg.)
17		299.05	287.68	1.488	Thiazole ring and phenyl ring puckering, CH3gp.vib.
16		273.67	263.27	5.0378	N22-H27, C2-N1, H24-C5, H25-C6, H26-C7 bend (wagg.)
15		263.93	253.9	17.3166	C14-Cl38 bend (twist.)
14		234.18	225.28	0.1638	C19-H32, N22-H27, C10-O23 bend (wagg.)
13		208.65	200.72	1.1349	Cl38-C4 bend (op), CH3gp.vib.
12		190.15	182.92	7.5202	C10-O23, C4-Cl38 bend (twist.), N22-C12 bend (wagg.), N22-H27 bend (wagg.)
11		152.61	146.81	1.2833	C4-Cl38 bend(twist.),C10-O23,C17-H29,C18-H21 bend (wagg.)
10		122.57	117.91	1.0412	C33-H36-H35-H34 bend (twist.), C10-O23 bend (wagg.)
9		119.12	114.59	0.4878	CH3gp.vib., phenyl ring puckering
8		114.57	110.21	0.3012	benzimidazole ring, phenyl ring, thiazole ring puckering
7		95.81	92.16	1.46	C33-H36-H35-H34 bend (twist.)
6		67.96	65.37	1.9938	C33-H36-H35-H34 bend (twist.)
5		45.31	43.58	0.0001	Phenyl ring bend (op), C10-O23 bend (wagg.)
4		42.99	41.35	0.186	benzimidazole ring, phenyl ring vib.
3		42.31	40.7	2.2709	C33-H36-H35-H34 bend (rock.)
2		25.82	24.83	0.0001	C33-H36-H35-H34 bend (rock.)
1		12.35	11.88	0.6297	C33-H36-H35-H34 bend (rock.)

Abbreviations: asym.-asymmetric, sym-symmetric, str-stretching, vib.-vibration, bend (ip)-in-plane bending, bend (op)-out-of-plane bending, wagg.-wagging, rock.-rocking, sciss-scissoring.

 

Vibrational Spectral Analysis:

The detailed vibrational assignments of fundamental modes of the title compound along with calculated IR intensities are reported in Table: 4. None of the predicted vibrational frequencies  have any imaginary frequency implying that the optimized geometry is located at the local minimum point on the potential energy surface. A potential energy surface is a mathematical relationship linking molecular structure and the resultant energy. For a diatomic molecule, it is a two - dimensional plot with the inter - nuclear separation on the x-axis and the potential energy at that bond distance on the y-axis, producing a curve. For larger systems, the surface has as many dimensions as there are degrees of freedom within the molecule. Generally, a non-linear N atomic molecule has 3N-6 degrees of freedom or internal coordinates. This is because all N atoms can move in three dimensions (x, y and z) giving 3N degrees of freedom. However six of those three translations in x, y and z directions and three rotations along x, y and z axes of the molecule as a whole do not produce any change in energy. The title molecule has 38 atoms and it has 96 degrees of freedom³⁴.

 

Methyl Group Vibrations:

The assignments of methyl group vibration make a significant contribution to the titled compound. The compound under investigation possesses a CH₃ group. For the assignments of CH₃ group frequencies one can expect that nine fundamentals can be associated to CH₃ group. The C-H stretching is at lower frequencies than those of aromatic ring. The asymmetric stretch is usually at higher wave number than the symmetric stretch. Usually the symmetrical bands are sharper than the asymmetrical bands. Methyl group vibrations are generally referred to as electron–donating substituent in the aromatic ring system, the anti symmetric C-H stretching mode of CH₃ is expected around 2980 cm^-1 and CH₃ symmetric stretching is expected at 2870 cm^{-1   35-37}.

 

C-N Vibrations:

The assignment of C-N stretching frequency is a rather difficult task since there are problems in identifying these frequencies from other vibrations. Silverstein³⁶ assigned C-N stretching vibrations in the region 1382-1266cm^-1. In the present work, the observed value at 1358cm^-1 and 1199cm^-1 in FT-IR spectra is assigned to C-N in- plane bending vibration. In the present study the theoretically computed values belonging to C-N stretching vibrations are good agreement with spectral data.

 

C-O Vibrations:

Generally the C-O vibrations occur in the region 1260-1000cm^{-1 38}. In the present study the C-O stretching vibrations are assigned at 1113cm^-1 which is in line with literature.

 

C-Cl Vibrations:

The vibrations belonging to the bond between the ring and halogen atoms were worth the discussion here since the mixing of vibrations are possible due to the lowering of the molecular symmetry and the presence of heavy atoms on the periphery of molecule³⁹. Generally the C-Cl absorption was obtained in the region 850-550cm^{-1 40}. Most of the aromatic chloro compounds had the strong to medium intensity in the region 385-265cm^-1 due to C-Cl bending vibration⁴¹. The FT-IR band identified at 375cm^-1 is assigned to the C-Cl bending vibration of the title compound.

 

C-C Vibrations:

The C-C stretching vibrations give rice to characteristic bands in the observed IR spectra, covering the spectral range from 1600 to 1400cm^-1.

 

C-H vibrations:

The hetero aromatic compounds and their derivatives are structurally very close to benzene. The C-H stretching vibrations of aromatic and hetero aromatic structures^{42, 43} in the region 3100-2900cm^-1 is for asymmetric stretching modes of vibrations. This permits the ready identification of the structure. Further in this region the bands are not much affected due to the nature and position of the substituent’s ^{44, 45}.

 

 

Stimulated IR Spectrum

 

HOMO-LUMO energy gap:

The HOMO –LUMO energy gap of a molecule will play an important role in determining its bioactive properties⁴⁶. The total energy, HOMO-LUMO energy, energy gap and dipole moment have influence on the stability of a molecule. We have performed optimization in order to investigate the energetic behavior and dipole moment of title compound. The total energy, and dipole moment have been calculated with B3LYP/6-31G level. The energy gap between the highest occupied and lowest unoccupied molecular orbital’s, is a critical parameter in determining molecular electrical transport properties because it is a measure of electron conductivity. The analysis of wave function indicates that the electron absorption corresponds to the transition from the ground to the first excited state and is mainly described by one election excitation from HOMO to LUMO. The HOMO energy characterizes the ability of election giving and the LUMO energy characterizes the ability of election accepting and the gap between HOMO and LUMO characterizes the molecular chemical stability. The energy gaps are largely responsible for the chemical and the spectroscopic properties of the molecules⁴⁷. All the HOMO and LUMO are placed symmetrically. The positive phase is red and the negative one is green. Moreover lower in the HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule.

 

The dipole moment in a molecule is another important electronic property which results from non-uniform distribution of charges on the various atoms in a molecule. It is mainly used to study the intermolecular interactions involving the Vander Waals type dipole - dipole forces, etc., because bigger the dipole moment, stronger will be the intermolecular interactions^48-50.

 

 

HOMO

 

LUMO

 

 

Mulliken charge distribution of 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole.

 

Mulliken Analysis:

The atomic charge in molecule is fundamental to chemistry. For instance, atomic charge has been used to

 

describe the process of electro negativity equalization and charge transfer in chemical reactions^{51, 52}.

 

CONCLUSION:

We have carried out DFT calculations on the structure and vibrational spectrum, HOMO, LUMO analysis of 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole comparison between the calculated and experimental structural parameters indicates that B3LYP results are in good agreement with experimental values. Vibrational frequencies and infrared intensities are calculated by DFT (B3LYP) levels of theory utilizing 6-31G method agree very well with experimental results. From the vibrational discussion, it was concluded that the substitution of H atom by Cl atom distorts the ring geometry to small extent and the planarity of the molecule. On the basis of agreement between the calculated and observed results, assignments of fundamental vibration modes of 2-(2-phenylaminothiazole-5-oyl)-N-methyl-6-chlorobenzimidazole are examined and some assignments were proposed. This study demonstrates that scaled DFT calculations are powerful approach for understanding the vibrational spectra of medium sized organic compounds. The C=C stretching vibrational frequencies are observed well within the expected range compared to the literature values. Among alkane C-H stretching vibrations, only some are expected in asymmetric range while others in symmetric range. But in the present case, all the observed bands for stretching lay in asymmetric range. These show that the vibrations of methyl group are not much affected by other substituents in the ring. The lowering of the HOMO-LUMO energy gap value has substantial influence on the charge transfer and bioactivity of the molecule.

 

ACKNOWLEDGEMENT:

T.F. Abbs Fen Reji thanks University Grants Commission, New Delhi for Financial Assistance in the form of Major Research project. The authors thank NIIST, Trivandrum and CDRI, Lucknow for spectral and analytical data.

 

REFERENCES:

1.      S.S. Mokle,  M.A.Sayeed and C. Kothawar, Int.J.Chem.Sci.,2, 96-100 (2004).

2.      P.Anbarasu and M. Arivazhagan, Indian J.Pune. Appl. Phys., 227-233(2011).

3.      V.H. Patel and S.A. Gandhi, J.Mol.Struct. 88-95 (2012).

4.      V. Arjunan, P.S. Balamourougane, C.V. Mythili, S. Mohan and V. Nandakumar, J.Mol. Struct., 247-258 (2011).

5.      J.V.N Vara Prasad,A. Pana Poulous and J.R. Rubin, Tetrahedron Lett.,41,4065 (2000).

6.      J. Gilbert, Elsevier App. Sci.Pups., London 1 (1984).

7.      S. Edrah, J.Appl. Cosmetol, 15,115 (1997).

8.      W. Rabb, J.Appl.Cosmetol, 15,115 (1997).

9.      C.Alkan, Y. Tek and D. Kahraman, Turk. J.Chem., 35,769 (2011).

10.   M. Kodomari,M. Suzuki,K. Tanigawa and T. Aoyama, Tetrahedron Lett., 46,5841 (2005).

11.   J.S. Ren, J. Diprose, J. Warren, R.M. Esnouf, L.E. Bird, S. Ikemizu, M Slater, J. Milton, J. Balzarini , D.L. Stuart and  D.K.Stammers,  J.Biol.Chem., 275,5633 (2000).

12.   F.T. Elmali, U. Avciata and N. Demirhan, Main Group Chem., 17 (2011).

13.   A.R. Katritzky and M.F. Gordee, , J.Chem.Soc., Perkin, 2199 (1991).

14.   M.Struga, J. Kossakowski, E. Kedzierska, S. Fidecka and J. Stefanska, Chem. Pharm.Bull., 55,796 (2007).

15.   A.D. Desai, D.H. Mahajan  and  K.H. Chikhalia, Ind.J.Che., 46B,1169 (2007).

16.   R.B Patel, K.H. Chikhalia, C. Pannecouque and E.D. Clercq, J.Braz.Chem.Soc., 18,312 (2007).

17.   G.A. Kilcigil and N. Altanlar, Turk.J.Chem., 30,223 (2006).

18.   S.Xue, J.S. Zou and H. Yong, Chin.Chem.Lett., 1119 (2000).

19.   C. Fengling, C. Yanrui, J. Hongxiz, Y. Xiaojun, F. Jing and L.Yan, Chinese Sci.Bull., 51,2201 (2006).

20.   S. Alyar, U.O. Ozmen,N. Karacan, O.S. Sentruk and K.A. Udachin, J.Mol.Struct., 889,144 (2008).

21.   A.D.Becke, Phys.Rev.A38, 3098 (1988).

22.   C.Lee, W.Yang, R.G. Parr, Phys. Rev.B 37, 1988, 785.

23.   A.D. Becke,  J.Chem.Phys., 98 (1993) 5648.

24.   J.P.Perdew, K.Burke and Y.Wang, Phy.Rev.B, 54 , 16533  (1996).

25.   J.P.Perdew, J.A.Chevary, S.H.Vosko, K.A.Jackson, M.R.Pederson, D.J.Singh and C.Fiolhais, Phy., Rev. B 48 , 4979 (E) (1993).

26.    Z.Zhengyu and D.Dongmei,  J.Mol.Struct. (Theochem.) 505, 247-249 (2000).

27.    Y.Carissan and W.Klopper, J.Mol.Struct. (Theochem) , 940, 15-118 (2010).

28.   M.H. Jamroaz  and  J.C.Dobrowolski, J.Mol.Struct., 565-566, 475-480 (2001).

29.   K.Burke, J.P.Perdew, Y.Wang, J.F.Dobson, G.Vignale and M.P.Das (Eds.), Electronic Density Functional Theory: Recent Progess and New Directions, Plenum Press, New York (1998).

30.   C.Adamo  and  V.Barone,  J.Chem.Phys. 108, 664-668 (1998).

31.   H.Arslan  and  O.Algul,  Spectrochem. Acta A 70, 2008, 109-116.

32.   J.B.Foresman, in and  E.Frisch (Ed.) Exploring Chemistry with Electronic Structure methods: A Guide to Using Gaussian, Gaussian Inc., Pittsburg, PA, (1996).

33.   R.Dennington, T.Keith and  J.Millam, Gaussview, Version 5 Semichem Inc., Shawnee Mission, KS, (2009).

34.   S. Shoghpour, A. Keykha, H.A. Rudbari, M. Rahimizadeh. M. Bakavoli, M.Pourayoubia  and  F. Nicolo, Acta Crystal.E,( 2012).

35.   M. Karabacak, D. Karagoz  and M. Kurt,  J.Mol.Struct. 892, 2008, 25-31(2008).

36.   R.M.Silverstein,G.C. Bassler and T.C. Morill, Spectrometric identification of organic compounds, 3^rd ed., John Wiley & Sons, New York, NY,239 (1974).

37.   J. Mohan, Organic Spectroscopy- Principles Applications, Narosa Publishing House, New Delhi, (2001).

38.   G.Varsanyi, Vibrational Spectra of Benzene Derivatives, Academic Press, New York, (1969).

39.    R.A. Yadeav and I.S.S ingh, Ind.J.Pune Appl. Phy.,23, 626-627 (1985).

40.   V. Arjunan and  S.  Mohan, J.Mol.Struct.,892, 289-299 (2008).

41.   V. Krishnakumar and N. Prabavathi, Spectrochem. Acta 72 A, 738-742 (2009).

42.   S. Gunasekaran. R.K. Nadarajan and K. Santhozam, Asian.J.Chem.,15, 1347 (2003).

43.    N.B.Clothup,L.H. Dely and S.E. Wiberly, Introduction to Infrared and Raman Spectroscopy,Vol.74, Academic Press, New York, 226 (1964).

44.   M. Fox, J.Chem.Soc.,3, 18 (1989).

45.   J.B. Wilson Jr , D.C. Decivs, and P.C. Cross, Molecular Vibrations, McGraw-Hill, New York, (1995).

46.   F. Jensen, Introduction to Computational Chemistry, Wiley Denmark, 2, 232 (2007).

47.    P.W. Atkins, Physical Chemistry, Oxford University Press, Oxford (2001).

48.   O.Prasad. L. Sinha, N. Misra, V. Narayan, N. Kumar and J. Pathak. J.Mol. Struct., 940, 82-86 (2010).

49.   B. Kosar and C. Albayrak, Spectrochim. Acta A 78, 160-167 (2011).

50.   B. Kosar, C.Albayrak, S. Demir, M. Odabasoglu and O. Buyukgungor, J.Mol.Struct.,  963, 211-218  (2010).

51.   K. Jug and Z.B. Maksic, Theoretical Model of Chemical Bonding, Part 3, Springer, Berlin, P.233 (1991).

52.   S. Fliszar, Charge Distributions and Chemical Effects, Springer, New York, (1983).

 

 

 

 

Received on 18.09.2018         Modified on 11.10.2018

Accepted on 10.11.2018         © AJRC All right reserved