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Keywords

FT-IR; FT-Raman; TED; NBO; T2CNH

Introduction

Generally, Pyridine ring is a heterocyclic organic compound with the chemical formula C₅H₅N. Pyridine is structurally related to benzene, with one methine group (=CH-) replaced by a nitrogen atom. It occurs in many important compounds, including azines and the vitamins niacin and pyridoxal. The precursor of pyridine is used to agrochemicals, pharmaceuticals and is also an important solvent and reagent. Mostly, it is used in the in vitro synthesis of DNA, sulfa pyridine (a drug against bacterial and viral infections), antihistaminic drugs tripelennamine and mepyramine, as well as water repellents, bactericides, and herbicides. Some chemical compounds, although not synthesized from pyridine, contain its ring structure. They include B vitamins niacin and pyridoxal, an anti-tuberculosis drug isoniazide, nicotine and other nitrogencontaining plant products [1].

The ring of Thiophene and its derivatives have been reported to possess broad spectrum of biological properties including anti-inflammatory, analgesic, antidepressant, antimicrobial and anticonvulsant activities [2-4]. Antiepileptic drugs (AEDs) like tiagabine, etizolam, brotizolam are containing thiophene moiety in their structures as active pharmacophore [5,6]. In addition, thiophene and its derivatives functionalized with the formyl group are versatile building blocks for the synthesis of donor– acceptor substituted p-conjugated systems for several optical applications.

The hydrazone group in the organic compound brings out several physical and chemical properties. The hydrazones are bearing the >C=N-N< which leads the molecule towards nucleophilic and electrophilic in nature. In the hydrazone moiety, the nitrogen atom behaves as nucleophilic and carbon atom behaves as nucleophilic as well as electrophilic in nature [7-9]. The benzohydrazide derivatives shows wide spectrum of biological activities such as antibacterial [10], antifungal [11] and antitubercular [12] activities.

Subashchandrabose et al. [13] recorded the FT-IR, FT-Raman and UV-Vis spectra for the molecule N1-N2-bis((pyridine-4-l) methylene)benzene-1,2-diamine. The observed FT-IR and FTRaman spectral values were compared with the calculated wave numbers. For the prediction of accurate vibrational assignments TED analysis was performed using SQM method. The bond lengths and bond angles of stable conformer were correlated well with the experimental values. The hyperconjugative interaction and charge delocalization around the bonds were studied using NBO analysis. Band gap energy was also determined.

Quantum chemical calculations of energies, geometrical structure and vibrational wavenumber of 1,2-bis(3-methoxy-4- hydroxybenzylidene)hydrazine were carried out by Subramanian et al. [14] using DFT method with 6-31G(d) as basis set. The optimized geometrical parameters obtained by DFT calculations are in good agreement with single crystal XRD data. The vibrational spectral data were obtained from FT-IR and FT-Raman spectra are assigned based on the results of the theoretical calculations in solid phase.

From Literature survey reveals that the vibrational analysis of (E)-N′-(thiophen-2-ylmethylene) nicotinohydrazide (T2CNH) has not yet been reported. The T2CNH molecule was synthesized and its structural characterization was calculated by B3LYP/6- 311++G(d,p) basis set. The spectral investigation such as FT-IR, FTRaman and UV-Vis spectra were recorded. The observed spectral results were compared with the computed wavenumber. The vibrational assignments of the title molecule were carried out with the help of TED. The First order hyperpolarizability, Homo- Lumo energy gap was calculated and furthermore, the MEP and thermodynamic properties were also calculated.

Computational Details

The entire theoretical calculations were performed DFT method at B3LYP/6-311++G(d,p) basis set to using Gaussian 03W [15] program package, invoking gradient geometry optimization [15,16]. The geometrical parameters were used in the vibrational frequency calculations at the same level to characterize all the stationary points as minima. The vibrationally averaged nuclear positions of T2CNH were used for harmonic vibrational frequency calculations resulting in IR and Raman frequencies together with intensities and Raman depolarization ratios. The vibrational modes were assigned on the basis of TED analysis using VEDA4 program package [17]. The Raman activity was calculated by using Gaussian 03W package and the activity was transformed into Raman intensity using Raint program [18] by the expression:

Where Ii is the Raman intensity, RAi is the Raman scattering activities, νi is the wavenumber of the normal modes and ν₀ denotes the wavenumber of the excitation laser [19].

Experimental Details

Synthesis procedure

A mixture of Thiophene-2-carboxaldehyde (2.1 mL, 0.01 mol) and nicotinic acid hydrazide (1.37 g, 0.01 mol) in 5 mL of ethanol was stirred in the presence of 2 drops of concentrated HCl for one hour. The reaction mixture was maintained at room temperature and the colourless solid was obtained. The solid was separated and filtered under suction, washed with ice-cold water (50 ml). The precipitate was washed with water and filtered and again washed with petroleum ether (40-60%) and dried over in a vacuum desicator then the product was recrystallized from hot ethanol.

Results and Discussion

Molecular Geometry

The T2CNH molecule was optimized by B3LYP/6-311++G(d,p) level of basis set. This molecule consists of thiophene and pyridine rings are fused by hydrazone linkage. The calculated bond length of C₂-S₁ is expected to be shorter than the C₅-S₁ bond length, since the hydrozone moiety is attached with C2 atom and their corresponding bond distances are 1.750 and 1.728Å. The bond lengths of C₂=C₃, C₃-C₄, C₄=C₅ are 1.377, 1.418, 1.369Å and the bond angles of C₂-C₃-C₄, C₃-C₄-C₅ are 113.02°, 113.03°. The bond angles S₁-C₂-C₃ and S₁-C₅-C₄ are differ by ~1° which is due to the shortening of bond distance between S₁ and C₂ atoms. These values are particularly in good agreement with the values of anti thiophen-2-aldehyde [20] and thiophen- 2-carbohydrazide [21]. Furthermore, these values are also find support from literature [22]. The dihedral angles of S₁-C₂-C₉-N₁₁/ S₁-C₂-C₉-H₁₀ and C₃-C₂-C₉-N₁₁/C₃-C₂-C₉-H₁₀ are -179.96°/-0.07° and 0.03°/+179.93°, respectively, which shows that the thiophen and hydrozone moieties of T2CNH are co-planar. Since there is a good conjugation between p-orbitals of all atoms of thiophen and hydrazone moieties. Most of the calculated geometrical parameters are find support from single crystal X-ray diffraction values [23,24]. It should be mentioned that there is no significant difference between the geometrical parameters of the hydrozone and pyridine moieties [23,24]. The geometrical parameters and optimized structure of the T2CNH molecule are presented in Table 1 and Figure 1, respectively.

Figure 1: The Optimized structure of (E)-N′-(thiophen-2-ylmethylene) nicotinohydrazide (T2CNH).

Bond Parametres	B3LYP/6-311++G(d,p)	XRDa,b,c
Bond Lengths (Å)
S1-C2	1.750	1.728b
S1-C5	1.728	1.717a, 1.707b
C2-C3	1.377	1.375a, 1.362b
C2-C9	1.448
C3-C4	1.418	1.431a, 1.392b
C3-H8	1.081	1.114a
C4-C5	1.369	1.345b
C9-H10	1.097	0.930c
C9-N11	1.282	1.266c
N11-N12	1.357	1.375c
N12-H13	1.016	0.860c
N12-C14	1.385	1.354c
C14-O15	1.213	1.224c
C16-C17	1.399	1.384c
C16-C18	1.397	1.3714c
C17-N19	1.335	1.3344c
C17-H20	1.087	0.9304c
C18-C21	1.387	1.3684c
C18-H22	1.083	0.9304c
N19-C23	1.335	1.3374c
C21-C23	1.395	1.3684c
C23-H25	1.086	0.9304c
Bond Angles (°)
C2-S1-C5	91.57	92.00a, 91.81b
S1-C2-C3	110.68	111.80a
C2-C3-C4	113.02	112.20a, 114.72b
C2-C3-H8	122.16	129.20a
C3-C4-C5	113.03	112.05b
S1-C5-C4	111.68	112.13b
N12-C14-C16	114.21	114.95c
O15-C14-C16	122.13	121.48c
C16-C17-N19	123.88	122.05c
C16-C17-H20	120.91	120.03c
N19-C17-H20	115.16	118.20c
C16-C18-C21	118.94	118.91c
C16-C18-H22	119.08	120.50c
C21-C18-H22	121.96	120.30c
C17-N19-C23	117.47	117.44c
C18-C21-C23	118.58	118.58c
C18-C21-H24	121.13	120.71c
C23-C21-H24	120.27	120.70c
N19-C23-C21	123.40	123.64c
Dihedral Angles (°)
S1-C2-C9-H10	-0.07
S1-C2-C9-N11	-179.96
C3-C2-C9-H10	179.93
C3-C2-C9-N11	0.03
C2-C3-C4-C5	0.02
C2-C3-C4-H7	-179.98
H8-C3-C4-C5	179.97
H8-C3-C4-H7	-0.03
C3-C4-C5-S1	-0.01
C3-C4-C5-H6	-179.99
H7-C4-C5-S1	179.99
H7-C4-C5-H6	0.01
C2-C9-N11-N12	179.45
H10-C9-N11-N12	-0.43
C9-N11-N12-H13	1.93
C9-N11-N12-C14	175.56
N11-N12-C14-O15	-2.82
N11-N12-C14-C16	177.89
H13-N12-C14-O15	170.80
H13-N12-C14-C16	-8.47
N12-C14-C16-C17	-28.41
N12-C14-C16-C18	154.27
O15-C14-C16-C17	152.29
O15-C14-C16-C18	-25.01
C14-C16-C17-N19	-178.88
C14-C16-C17-H20	-0.97
C18-C16-C17-N19	-1.57

^aBrathenO, KvesethK, NielsenKJ, HagenK (1986) J MolStruct 145: 45.
^bGeigerDK, GeigerHC, WilliamsL, NollBC (2012) ActaCrystE 68 : 0420.
^cRameshBabuN (2014) J MolStruct 1072: 84-93.

Table 1: The optimized bond parameters of T₂CNH.

Vibrational Assignments

The T2CNH molecule belongs to C1 point group symmetry. It consists of 25 atoms which undergoes 69 normal modes of vibrations. In which 47 modes of vibrations are in-plane and 22 are out-of-plane bending vibrations and all of them are IR and Raman active [25]. The calculated and observed vibrational wavenumbers using DFT/B3LYP/6-311++G(d,p) basis set, along with their relative intensities are given in Table 2. The total energy distribution (TED) was calculated using SQM program [26]. The combined vibrational spectra of T2CNH molecule are shown in Figures 2 and 3.

Figure 2: The Theoretical and Experimental FT-IR spectra of T₂CNH.

Figure 3: The Theoretical and Experimental FT-Raman spectra of T₂CNH.

N₁₂(34)

Mode No	Calculated Frequencies (cm-1)		Observed           Frequencies (cm-1)		IR Intensity		Raman Intensity		Reduced Masses	Force Consts	Vibrational assignments≥10% (TED)d
	Un Scaled	Scaleda	FT-IR	FT-Raman	Abs.	Rel.b	Abs.	Rel.c
1	3503	3365	3401 w		7.42	2.06	134.41	1.67	1.08	7.78	νN12H13(100)
2	3247	3120	3171 w		1.23	0.34	101.27	1.26	1.10	6.82	νC5H6(94)
3	3223	3096			0.57	0.16	34.50	0.43	1.10	6.70	νC3H8(97)
4	3204	3078		3079 w	6.29	1.75	62.54	0.78	1.09	6.59	νC4H7(96)
5	3202	3076			7.00	1.94	72.48	0.90	1.10	6.62	νC18H22(99)
6	3187	3062	3059 w		9.14	2.54	84.20	1.05	1.09	6.53	νC21H24(95)
7	3156	3032			10.92	3.03	72.05	0.89	1.09	6.39	νC23H25(92)
8	3139	3016			29.24	8.12	29.47	0.37	1.09	6.32	νC17H20(99)
9	3019	2901			42.64	11.84	29.11	0.36	1.09	5.83	νC9H10(100)
10	1757	1688	1673 s	1670 w	360.16	100.00	392.18	4.87	11.08	20.16	νO15C14(85)
11	1656	1591	1592 s	1589 s	15.73	4.37	8057.31	100.00	7.23	11.68	νN11C9(75)+βH10C9N11(20)
12	1627	1563			32.79	9.10	1339.53	16.63	5.75	8.96	νC18C21(30)+νN19C23(30)+βC21C23N19(25)
13	1605	1542	1549 w		6.21	1.73	25.40	0.32	5.21	7.91	νC21C23(31)+νC16C18(27)+βC17N19C23(10)
14	1570	1508		1519 w	217.56	60.41	126.25	1.57	3.38	4.91	νC2C3(28)+βH13N12N11(22)+νC4C5(13)+νC2C9(11)
15	1551	1490			202.85	56.32	2133.94	26.48	2.19	3.10	νC2C3(14)+βH13N12N11(41)+νC4C5(12)
16	1506	1447	1425 m	1429 m	26.23	7.28	58.60	0.73	2.15	2.87	βH24C21C23(27)+βH20C17C16(25)
17	1459	1402			8.66	2.41	4817.87	59.80	4.83	6.07	νC2C3(13)+νC4C5(32)+βH7C4C5(14)+νC3C4(15)
18	1448	1391			26.37	7.32	62.23	0.77	2.18	2.69	βH25C23N19(43)+βC16C17N19(23)
19	1390	1335			52.04	14.45	1478.54	18.35	1.75	1.99	νC4C5(13)+βH10C9N11(38)+βH6C5C4(13)
20	1387	1333			16.34	4.54	60.17	0.75	2.08	2.36	βH10C9N11(25)+βH6C5C4(15)+νC3C4(18)
21	1362	1308	1290 s	1300 m	0.98	0.27	2.27	0.03	1.31	1.43	βH20C17C16(45)+βH22C18C21(23)
22	1291	1240		1241 w	19.71	5.47	141.74	1.76	7.28	7.15	νN19C23(43)+νC16C18(27)
23	1268	1219	1218 m	1225 w	94.23	26.16	45.69	0.57	1.54	1.46	βH7C4C5(23)+βH8C3C4(29)+βH6C5C4(13)
24	1265	1215			221.71	61.56	2432.18	30.19	2.39	2.25	νC14C16(22)
25	1221	1173		1195 w	39.47	10.96	610.76	7.58	1.60	1.40	νC18C21(11)+βH24C21C23(17)+βH25C23N19(30)
26	1195	1148	1145 m	1149 w	87.67	24.34	456.90	5.67	3.39	2.85	νN11N12(60)
27	1142	1097		1096 w	146.68	40.73	527.62	6.55	2.70	2.07	νC2C9(10)+νN12C14(40)
28	1134	1090			69.91	19.41	242.18	3.01	1.45	1.10	βH24C21C23(20)+βC16C17N19(12)+βH22C18C21(36)
29	1102	1059			7.47	2.07	295.96	3.67	1.26	0.90	νC4C5(15)+βH7C4C5(22)+βH6C5C4(47)
30	1086	1044			5.12	1.42	134.46	1.67	3.17	2.21	νN11N12(24)+νN12C14(16)
31	1058	1017	1031 w	1030 w	1.76	0.49	393.20	4.88	3.19	2.11	βC16C18C21(45)
32	1056	1015			7.59	2.11	414.19	5.14	1.76	1.15	βH7C4C5(14)+βH8C3C4(27)+νC3C4(35)
33	1039	999			11.95	3.32	318.45	3.95	4.30	2.73	βC17N19C23(32)+βC21C23N19(15)+βC18C21C23(25)
34	1014	974			2.23	0.62	6.67	0.08	1.38	0.83	τH22C18C21H24(75)+ΓC23C21N19H25(18)
35	987	949	948 w	955 w	0.58	0.16	8.33	0.10	1.43	0.82	ΓC23C21N19H25(50)+ΓC17C16N19H20(12)+ΓC18C16C21H22(30)
36	947	910			1.90	0.53	6.99	0.09	1.39	0.73	ΓC17C16N19H20(71)
37	945	908		904 w	9.84	2.73	50.68	0.63	1.50	0.79	ΓH10C9N11H12(80)
38	928	891	897 w		0.39	0.11	6.15	0.08	1.38	0.70	τH6C5C4H7(46)+ΓC3C2C4H8(32)
39	921	885			38.10	10.58	86.38	1.07	7.12	3.56	βN12C14O15(20)+βC14N12N11(25)
40	861	827	846 w		31.22	8.67	114.39	1.42	4.31	1.88	βC4C5S1(80)
41	851	817			8.44	2.34	1.04	0.01	1.29	0.55	τH6C5C4H7(36)+ΓC3C2C4H8(55)
42	841	808			13.98	3.88	48.48	0.60	1.97	0.82	τH22C18C21H24(17)+ΓC23C21N19H25(12)+ΓC18C16C21H22(32)+ΓO15C16N12C14(12)
43	823	791			25.89	7.19	107.27	1.33	4.43	1.77	νC2C3(10)+βC2C9N11(20)+νS1C2(17)
44	747	718			3.22	0.89	221.87	2.75	7.15	2.35	βC2C3C4(57)+νS1C2(23)
45	739	710	700 w		31.92	8.86	64.22	0.80	2.76	0.89	ΓC18C16C21H22(25)+ΓO15C16N12C14(50)
46	724	695			21.84	6.06	20.02	0.25	4.31	1.33	βC21C23N19(17)+τC16C17C23N19(16)+τC16C18C23C21(16)+τC18C21N19 C23(10)
47	718	690			16.37	4.54	7.30	0.09	3.96	1.20	τC16C17C23N19(27)+τC16C18C23C21(22)+τC18C21N19 C23(16)
48	706	679		652 w	75.61	20.99	10.36	0.13	1.17	0.34	τH6C5C4H7(13)+τH6C5S1C2(81)
49	633	608	607 s		4.00	1.11	49.48	0.61	7.72	1.82	βC16C17N19(15)+βC17N19 C23(15)+βC18C21C23(41)
50	610	586			2.58	0.72	360.42	4.47	9.05	1.98	βC2S1C5(63)
51	586	563			1.22	0.34	16.70	0.21	3.25	0.66	τC3C2C4H5(79)
52	528	507	503 m		15.76	4.38	167.78	2.08	3.01	0.49	βC16C14N12(22)+τH13N12C14C16(22)+ΓC14C16C18C17(10)
53	508	488			44.93	12.47	72.78	0.90	1.60	0.24	τH13N12C14C16(61)
54	492	472			0.31	0.09	8.91	0.11	4.01	0.57	τC2S1C4C5(65)
55	451	433			0.46	0.13	24.54	0.30	7.97	0.95	βC2C9N11(14)+νS1C2(12)+βC17,C16C18(10)+βC9C2S1 (12)+βC14N12N11(11)
56	419	402			7.99	2.22	9.91	0.12	4.68	0.48	τC16C17C23N19(15)+τC16C18C23C21(31)
57	396	381			4.89	1.36	11.97	0.15	3.36	0.31	τC16C18C23C21(16)+τC18C21N19C23(34)+ΓC14C16C18C17(10)
58	379	364			1.32	0.37	1.86	0.02	8.03	0.68	νC14C16(17)+βN12C14O15(22)+βC17C16C18(20)
59	340	326			1.88	0.52	29.62	0.37	5.99	0.41	τC2S1C4C5(18)+ τC2C9N11
60	264	253			13.84	3.84	34.50	0.43	4.73	0.19	βC14C16C18(36)
61	226	217		224 w	11.59	3.22	71.81	0.89	3.69	0.11	τC5S1C2C9(11)+ΓC16C14N12N11(20)+τC3C2C9N11(16)
62	213	205		191 w	1.15	0.32	136.24	1.69	10.18	0.27	βC9 C2S1(30)+βC14N12N11(22)
63	170	163			11.98	3.33	135.90	1.69	4.69	0.08	τC9 N11N12C14(20)+ΓC14C16C18C17(14)+τC3C2C9N11(13)
64	130	125			1.52	0.42	83.59	1.04	5.74	0.06	τC9N11N12zC14(25)+τC5S1C2C9 (37)+ΓC14C16C18C17(10)
65	120	115			6.55	1.82	60.10	0.75	5.71	0.05	βC2C9N11(18)+βC16C14N12(18)+βC9C2S1(17)+ΓC14C16C18C17(14)
66	64	61		80 m	5.89	1.63	381.03	4.73	5.90	0.01	τC5 S1C2C9(12)+τC18 C16C14N12(45)+τC3C2C9N11(15)
67	46	45			0.73	0.20	161.56	2.01	6.68	0.01	βC2C9N11(16)+βC16C14N12(14)+βC9N11N12(20)+βC14N12N11(22)
68	32	31			1.86	0.52	329.50	4.09	5.69	0.00	τC2 C9N11N12(18)+τC18C16C14N12(15)+τC16 C14N12N11(49)
69	27	26			0.47	0.13	967.33	12.01	5.46	0.00	τC9 N11N12C14(18)+τC18 C16C14N12(25)+τC3 C2C9N11(18)

ν: Stretching, β: in-plane-bending, Γ: out-of-plane bending, τ- Torsion, vw: very week, w:week, m:medium, s:strong, vs: very strong.
^aScaling factor: 0.9608.
^bRelative IR absorption intensities normalized with highest peak absorption equal to 100.
^cRelative Raman intensities calculated by Equation (1) and normalized to 100.
^dTotal energy distribution calculated at B3LYP/6-311++G(d,p) level.

Table 2: The experimental and calculated frequencies of T₂CNH using B3LYP/6-311++G(d,p) level of basis set [harmonic frequencies (cm⁻¹), IR, Raman intensities (Km/mol), reduced masses (amu) and force constants (mdynA^°−1)].

N-H vibrations

The N-H stretching vibration appears in the region of 3300-3500 cm^-1 [27]. In accordance with the above literature the νN-H vibration has been observed at 3401 cm^-1 in FTIR spectrum, whereas the harmonic wavenumber assigned at 3365 cm^-1 (mode no: 1) and its TED value is 100% it should be noted here that, a small deviation between theoretical and experimental value is only due to intra-molecular charge transfer between amino and carbonyl group in hydrazone linkage. The harmonic wavenumbers (1508/ mode no: 14 and 488 cm^-1/mode no: 53) of βN-H and ΓN-H modes were presented in Table 2 are found to be in good agreement with literature [28] data 1476 and 535 cm^-1 as well as with the structurally related molecule. Mode no: 14 is in agreement with observed FT-Raman band at 1519 cm^-1 and these assignments also find support from TED values (22% and 61%).

C-H vibrations

In aromatic compounds, the νCH, βCH and ΓCH vibrations are expected to appear in the ranges of 3100-3000 cm^-1, 1400-1000 cm^-1 and 1000-750 cm^-1, respectively [29,30]. In this study, the aromatic C-H stretching vibration is observed at 3059 cm^-1 /FT-IR, whereas the calculated wavenumbers are in the range 3076-3016 cm^-1 (mode nos. 5 and 9). The in-plane C-H bending vibrations are assigned at 1425, 1290 cm^-1 in FT-IR and 1429, 1300 & 1195 cm^-1 in FT-Raman spectra and their corresponding calculated wavenumbers are 1447, 1391, 1308, 1173 cm^-1 (mode nos: 16, 18, 21, 25). The harmonic wavenumbers occur in the region of 974-808 cm^-1 (mode nos: 34-36, 42) are assigned to C-H out-ofplane bending modes, in which mode no: 35 is in agreement with observed wavenumber values: 955 cm^-1 (FT-Raman) and 948 cm^-1 (FT-IR). These assignments are in line with literature values [14] and also find support from TED Values.

The νCH modes are expected to appear in the range of 3100- 3000 cm^-1 with multiple weak bands and the bands are not affected appreciably by the nature of the substituent’s [31,32]. The νC-H vibration of the thiophen ring is observed at 3171 cm^-1 in FT-IR and 3079 cm^-1 in FT-Raman spectra in accordance with the literature [20-22]. The harmonic values corresponding to νC-H are calculated in the range 3120-3078 cm^-1 (mode nos: 2-4) with TED values >96%. This indicates that these are highly pure stretching modes. The βC-H vibrations appear by sharp but weak to medium bands in the range 1100-1500 cm^-1 and the bands are not sensitive to the nature of substitutents. The ΓC-H deformation modes are expected to appear in the range 800-1000 cm^-1 [32]. The IR active βC-H/ΓC-H vibrations of T2CNH molecule are observed at 1218/897 cm^-1, respectively. The harmonic wavenumbers of these bands are 1219, 1059, 1015 and 891, 817 cm^-1 in good agreement with literature values [20-22].

The harmonic frequencies for νC-H, βC-H and ΓC-H modes in hydrozone linkage were assigned at 2919, 1315 and 910 cm^-1, respectively and these assignments are in line with assignments νC-H: 2901, βC-H: 1335, ΓC-H: 908 cm^-1 (mode nos: 9, 19, 37) are made in the present study. These vibrational assignments are further supported by literature [28] and TED output.

C=C, C-C vibrations

In the pyridine ring, the ν(C-C) stretching vibrations are usually occur in the ranges of 1590-1640, 1560-1580 and 1470-1510 cm^-1 [33]. The computed wavenumber for ν(C-C) modes are lies at 1563, 1542, 1240 and 1173 cm^-1 (mode nos: 12, 13, 22 and 25) with TED values. In the present study it has been established well and the FTIR band at 1549 cm^-1 and FT-Raman bands at 1241, 1195 cm^-1 are designated as νC-C vibrations. These assignments are find support from the literature [34] and also from TED values.

The bands arising from βCCC and ΓCCC of pyridine moiety are ascribed to bands observed at 1031, 607 and 503 cm^-1 respectively in FTIR spectrum. These vibrational assignments find support from harmonic bands: 1017, 999, 608 and 507, 381, 163 cm^-1 (mode nos: 31, 33, 49 and 52, 57, 63) in addition to literature values [35].

The ring carbon-carbon stretching vibrations in thiophen ring are reported in the ranges of 1329-1431, 1420-1501 and 1419-1519 cm^-1, respectively [20-22]. For the same mode the computed wavenumbers are: 1508 (C=C), 1490 (C=C) and 1402 cm^-1 (C-C). These assignments are having considerable TED values ≥ 15% and its corresponding mode no: 14 is further supported by observed Raman band 1519 cm^-1. The βCCC mode of thiophene moiety is ascribed to mode no: 44 (718 cm^-1), this supported by TED value (57%) also. The mode nos: 27 and 24 are attributed to νC₂-C₉ and νC₁₄-C₁₆ mode and are in agreement with literature [28].

C=N, C-N vibrations

The identifications of C=N and C-N vibrations is a difficult task, since the mixing of vibrations is possible in this region [36]. However, with the help of Gauss View (3.0) software and TED results, those vibrations are described and assigned in this study. The C=N and C-N stretching vibrations appear in the ranges of 1670-1600 cm^-1 and 1382-1266 cm^-1 respectively [36]. In hydrozone linkage, the νC9=N11 and νC14-N12 stretching vibrations are assigned respectively at 1592 cm^-1 (FTIR) /1589 cm^-1 (FT-Raman) and at 1096 cm^-1 (FT-Raman). The TED results show that these vibrations are mixed with βHCN and νC-C modes and their corresponding harmonic frequencies are 1591 (mode no: 11) and 1097 cm^-1 (mode no: 27) well correlated with experimental observations. These vibrational assignments are also supported by literature [28] in addition to TED output (75% and 40%).

In pyridine ring, the harmonic/observed bands at 1563 (mode no: 12), 1240 (mode no: 22)/1241 cm^-1 in FT-Raman spectrum can be assigned to C-N stretching vibration and TED also predict that these vibrations are mixed with νC-C modes. These assignments are in good agreement with our earlier study [28] and also find support from TED values (30%, 43%). The βC₂₁-C₂₃-N₁₉, βC₁₆-C₁₇-N₁₉, βC₁₇-N₁₉-C₂₃ and βC₂-C₉=N₁₁, βC₁₆-C₁₄-N₁₂ deformations belong to pyridine and hydrozone moieties, respectively assigned to 1563, 1391, 999 and 791, 507 cm^-1 (mode nos: 12, 18, 33 and 43, 52). Similarly the τC₁₆C₁₇C₂₃N₁₉, τC₁₈C₂₁N₁₉C₂₃, τC₃C₂C₉N₁₁, ΓC₁₆C₁₄N₁₂N₁₁ modes are assigned to wavenumbers: 690, 381, 217, 217 cm^-1 (mode nos: 47, 57, 61, 61).

N-N vibrations

The νN-N stretching was observed at 1145 cm^-1 in FTIR is undoubtedly assigned to νN₁₁-N₁₂ vibration and the value of this band is calculated at 1148 cm^-1 (mode no: 26) with a TED of (60%) [28]. This assignment is well correlated with observed FT-Raman band 1149 cm^-1. The in-plane bending vibrations of C₂-C₉=N₁₁, C₉=N₁₁-N₁₂ & C₁₄-N₁₂-N₁₁ are assigned to wavenumbers: 791, 45 & 885, having considerable TED values (≥ 20%). The wavenumbers 163, 326 cm^-1 (mode nos: 63, 59) are assigned to τC₉=N₁₁-N₁₂-C₁₄, τC₂-C₉=N₁₁-N₁₂ modes.

C-S vibrations

In T2CNH the scaled wavenumbers 791 and 718 cm^-1 (mode nos: 43 and 44) are assigned to νC-S modes of thiophen ring moiety. This assignment is in agreement with the assignments proposed by various authors [20,21]. This mode is well known to mix with neighboring modes (νCC, βCCN/mode no: 43 and βCCC/mode no: 44) as reported in the literature [37]. The harmonic frequencies of βCSC and ΓCSC vibrations are ascribed to wavenumbers: 586 cm^-1 (mode no: 50) and 125 cm^-1 (mode no: 64) with 62% and 37% of TED values, respectively. Further the wavenumbers 827 cm^-1 (mode no: 40) and 205 cm^-1 (mode no: 62) are assigned to βC₄C₅S₁ and βC₉C₂S₁ modes, respectively, which are in line with the observed bands (846 cm^-1: FTIR and 191 cm^-1: FT-Raman) in addition to support the TED values [80% and 30%].

C=O vibrations

The C=O is formed by Pπ-Pπ bonding between carbon and oxygen atoms. Carbonyl (C=O) group stretching vibration is expected to appear in the region of 1680-1715 cm^-1 [38]. In this study, the carbonyl group stretching vibration appear at 1670 cm^-1 as strong band in FT-IR and at 1673 cm^-1 as weak band in FT-Raman spectra. The values of νC=O band is calculated at 1688 cm^-1 (mode no: 10) with a TED of 85%. The βC=O and ΓC=O vibrations are assigned respectively to mode nos: 39 and 45, in which the predicted wavenumber related to ΓC=O mode is found to be in moderate agreement with the observed FTIR band at 700 cm^-1.

NLO Property

Analysis of organic compounds having conjugated π-electron systems and large hyperpolarizability using IR and Raman spectroscopy has evolved as a subject of scientific research. The application of the title molecule in the field of non-linear optics demands the investigation of its structural and bonding features contributing to the hyperpolarizability enhancement by analyzing the vibrational modes using IR and Raman spectroscopy. The DFT/ B3LYP/6-311++G(d,p) basis set has been used for the prediction of first hyperpolarizability.

The calculated first hyperpolarizability and the total molecular dipole moment of T2CNH is 1.5861 × 10⁻³⁰ esu, 0.9906 Debye, respectively obtained by B3LYP/6-311++G(d,p) level of theory. The total dipole moment of the title molecule is moderately equal and β0 value of T2CNH is 4 times greater than that of urea, hence the molecule T2CNH has considerable non-linear optical (NLO) activity and the hyperpolarizabilities of T2CNH are given in Table 3.

Parameters	B3LYP/6-311++G(d,p)
Dipole moment ( μ )                            Debye
μx	0.3145
μy	-0.7701
μz	0.5380
μ	0.9906Debye
Polarizability ( α0  )× 10-30esu
αxx	330.88
αxy	-3.11
αyy	168.52
αxz	-4.63
αyz	-0.11
αzz	97.39
α0	0.5318x10-30esu
Hyperpolarizability( β0 )× 10-30esu
βxxx	-1853.85
βxxy	229.60
βxyy	-33.45
βyyy	-129.96
βxxz	40.31
βxyz	21.11
βyyz	2.92
βxzz	54.46
βyzz	-29.90
βzzz	-38.55
β0	1.5861x10-30esu

Standard value for urea (μ=1.3732 Debye, β₀=0.3728 × 10^-30 esu): esu-electrostatic unit

Table 3: The NLO measurements of T2CNH.

NBO Analysis

This method gives information about the intra- and inter-molecular interactions among bonds. Furthermore, it provides a convenient basis for investigating the interactions in both filled and virtual orbital spaces along with charge transfer and conjugative interactions in molecular system [39]. The natural bonding orbital (NBO) analysis was performed for T2CNH using B3LYP/6- 311++G(d,p) basis set in order to elucidate the intra-molecular, hybridization and delocalization of ED within T2CNH. The strong intra-molecular hyperconjugative interaction of the σ and π electrons of C−C to the anti C−C bond of the pyridine ring leads to stabilization of some part of the pyridine ring. The NBO analysis has been carried out by B3LYP/6-311++G(d,p) basis set and the E(2) values and types of the transition are shown in Table 4.

Type	Donor NBO (i)	ED/e	Acceptor NBO (j)	ED/e	E(2) kJ/mol	E(j)-E(i) a.u.	F(i,j) a.u.
π -π*	BD (2) C2 - C3	1.795	BD*(2) C4 - C5	0.309	69.58	0.28	0.06
			BD*(2) C9 - N11	0.209	76.65	0.28	0.06
σ -σ*	BD (1) C3 - H8	1.972	BD*(1) S1 - C2	0.028	23.39	0.73	0.06
			BD*(1) C2 - C3	0.021	7.57	1.12	0.04
			BD*(1) C4 - C5	0.014	8.08	1.11	0.04
π -π*	BD (2) C4 - C5	1.846	BD*(2) C2 - C3	0.351	66.02	0.30	0.06
σ -σ*	BD (1) C4 - H7	1.976	BD*(1) S1 - C5	0.017	18.95	0.75	0.05
			BD*(1) C2 - C3	0.021	8.03	1.12	0.04
			BD*(1) C4 - C5	0.014	5.73	1.12	0.04
π -π*	BD (2) C14 - O15	1.980	BD*(2) C16 - C17	0.335	15.10	0.40	0.04
π -π*	BD (2) C16 - C17	1.633	BD*(2) C14 - O15	0.277	65.98	0.3	0.06
			BD*(2) C18 - C21	0.277	89.54	0.29	0.07
			BD*(2) N19 - C23	0.366	69.71	0.27	0.06
π -π*	BD (2) C18 - C21	1.636	BD*(2) C16 - C17	0.335	74.85	0.28	0.06
			BD*(2) N19 - C23	0.366	122.13	0.27	0.08
π -π*	BD (2) N19 - C23	1.706	BD*(2) C16 - C17	0.335	112.97	0.32	0.08
			BD*(2) C18 - C21	0.277	52.59	0.33	0.06
n -π*	LP (2) S1	1.622	BD*(2) C2 - C3	0.351	87.15	0.27	0.07
			BD*(2) C4 - C5	0.309	91.55	0.26	0.07
n -π*	LP (2) N12	1.667	BD*(2) C9 - N11	0.209	115.14	0.29	0.08
			BD*(2) C14 - O15	0.017	4.44	0.88	0.03
			BD*(2) C14 - O15	0.277	190.41	0.32	0.11
n -σ*	LP (1) O15	1.855	BD*(1) N12 - C14	0.084	118.2	0.67	0.12
			BD*(1) C14 - C16	0.069	80.37	0.66	0.10
n -σ*	LP (1) N19	1.916	BD*(1) C16 - C17	0.033	39.33	0.90	0.08

Table 4: The second order perturbation theory analysis of Fock Matrix in NBO basis for T2CNH.

The larger E(2) value shows the intensive interaction between electron donors and electron acceptors. The strong intramolecular hyper conjugative interactions of the σ and π electrons of the C=C, C=N to the anti C=C, C=N bond of the ring as well as C=O group leads to stabilization of some part of the ring system in T₂CNH. In the present study, the π-character of the bond plays an important role on comparing with σ bond character. The hyper conjugative interactions π(C₂-C₃)→π*(C₉-N₁₁), π(C₄- C₅)→π*(C₂-C₃), π(C₁₆-C₁₇)→π*(C₁₈-C₂₁), π(C₁₈-C₂₁)→π*(N₁₉-C₂₃), π(N₁₉-C₂₃)→π*(C₁₆-C₁₇) and π(C₁₄-O₁₅)→π*(C₁₆-C₁₇) transfer stabilization energy: 76.65, 66.02, 89.54, 122.13, 112.97 and 15.10 KJ/mol to the molecular system. The lone pair of sulphar, nitrogen and oxygen atoms play great role in T₂CNH molecule. The S₁, N₁₂ & O15 atoms transfer maximum energy 91.55, 190.41 and 118.20 KJ/mol to (C₄-C₅), (C₁₄-O₁₅) & (N₁₂-C₁₄) bonds, respectively. The maximum hyperconjucative E(2) energy of heteroatoms during the inter-molecular interaction leads the molecule towards medicinal and biological applications [28]. The bond σ(C₃-H₈) transfer more energy (23.39 KJ/mol) to σ*(S₁-C₂) bond on comparing with energy transfer (18.95 KJ/mol) from σ(C₄-H₇) to σ*(S₁-C₅). Hence the ν(S₁-C₂) mode observe at higher frequency 791 cm^-1 (mode no: 43) than the ν(S₁-C₅) mode (718 cm^-1/mode no: 44).

HOMO-LUMO Analysis

The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) analysis is very important parameters for quantum chemistry. The energy values of HOMO (π-donor) and LUMO (π-acceptor) and its energy gap which reflects the chemical activity of the molecule. The HOMO and LUMO energy was calculated by B3LYP/6-311++G(d,p) level of theory. The frontier molecular orbitals (FMOs) of T2CNH are listed in Table 5. The atomic compositions of FMOs are shown in Figure 4. The HOMO is located over the thiophene and hydrozone moieties. The LUMO is located over pyridine ring. The LUMO transition implies that an ED transfer to pyridine ring via hydrazone linkage. The HOMO and LUMO energies are predicted as -6.248 eV and -2.223 eV, respectively. The calculated HOMOLUMO energy gap is 4.025 eV, which explains the eventual charge transfer taking place within the present molecule. The physicochemical properties are also listed in Table 6.

Figure 4: The frontier molecular orbitals for T₂CNH.

Occupancy	Orbital energies (a.u)	Orbital energies (eV)	Kinetic energies (a.u)
O56	-0.292	-7.947	1.641
O57	-0.284	-7.740	1.641
O58	-0.271	-7.390	1.582
O59	-0.269	-7.342	2.186
O60	-0.229	-6.248	1.567
V61	-0.081	-2.223	1.590
V62	-0.055	-1.503	1.586
V63	-0.055	-1.503	1.424
V64	-0.019	-0.519	0.488
V65	-0.009	-0.255	0.535

Table 5: The frontier molecular orbital of T₂CNH.

Parameters	Values
HOMO	-6.248 eV
LUMO	-2.223 eV
Energy gap	4.025 eV
Ionization potential (IP)	6.248 eV
Electron affinity (EA)	2.223 eV
Electrophilicity Index (ω)	2.562
Chemical Potential (µ)	7.359
Electro negativity (χ)	-7.359
Hardness (η)	-4.025

Table 6: The Physico-Chemical properties of T₂CNH.

UV-Vis Spectral Analysis

The UV-Visible absorption spectrum of T2CNH was recorded in the range of 250-350 nm is shown in Figure 5. All the structures allow strong π-π* (or) σ-σ* transition in the UV-Vis region with high extinction coefficients. On the basis of fully optimized ground state structure at TD-DFT/B3LYP/6-311++G(d,p) calculation has been used to determine the low-lying excited states of T2CNH. The calculated results involving the vertical excitation energies, oscillator strength (f) and wavelength are carried out and compared with measured experimental wavelength. Typically, according to Franck-Condon principle, the maximum absorption peaks (λmax) in a UV-Vis spectrum corresponds to vertical excitation. It is evident from the Table 7 that the calculated absorption maxima values have been found to be 332, 301 and 286 nm which correlates well with the experimental values 340 and 290 nm. The more intense band at 340 nm has maximum oscillator strength (f=0.6909), corresponds to Homo-Lumo transition and is mostly characterized as n-π* type. This type of transition is attributed to the presence of large no of free lone pairs of electrons available on sulphar (S₁), Nitrogen (N₁₁, N₁₂) and oxygen (O₁₅) atoms. The experimental and theoretical UVVis absorption spectrum is shown in Figure 5. The density of states spectrum of T2CNH is shown in Figure 6. It was used to calculate group contributions to the molecular orbitals (HOMO and LUMO). DOS plot shows population analysis per orbital and demonstrates a simple view of the character of the molecular orbitals (MOs) in a certain energy range.

Figure 5: The Theoretical and Experimental UV-Visible spectra of T₂CNH.

Figure 6: The DOS spectrum of T₂CNH.

Calculated at B3LYP/ 6-311++G(d,p)	Oscillator strength	Calculated Band gap (ev/nm)	Experimental Band gap (nm)	Type
Excited State   1	Singlet-A (f=0.6909)	3.7311 eV/332.30 nm	340	π-π*
60 -> 61	0.6388	-4.0254
60 -> 62	0.1325	-4.7451
Excited State   2	Singlet-A (f=0.0043)	4.1118 eV/301.54 nm
59 -> 61	0.6467	-5.1187
59 -> 62	0.1819	-5.8384
Excited State   3	Singlet-A (f=0.0126)	4.3234 eV/286.77 nm	290	π-π*
60 -> 62	0.4175	-4.7451
60 -> 63	0.5580	-4.8692

Table 7: The electronic transition of T₂CNH.

MEP Analysis

The molecular electrostatic potential (MEP) is widely used as a reactivity map displaying most probable regions for the electrophilic attack of charged part on organic molecule. MEP plot provides a simple way in predicting the interaction of different geometries. In order to predict the reactive sites for electrophilic and nucleophilic attacks of the T₂CNH, MEP was calculated with DFT/B3LYP/6-311++G(d,p) level of theory. The negative (red color) and positive (blue color) regions of MEP are related to electrophilic and nucleophilic reactivity respectively is shown in Figure 7. The negative region is located over the carbonyl group and the positive region is located over Hydrogen atom in the hydrazone linkage.

Figure 7: Molecular electrostatic potential map of T₂CNH.

Mulliken Charges Analysis

The Mulliken atomic charge calculation has an important role in the application of quantum chemical calculation to molecular system, because the atomic charges should affect dipole moment, polarizability, electronic structure and more a lot of properties of molecular systems. The total atomic charges of T2CNH are calculated by Mulliken population analysis with B3LYP/6-311++G (d,p) basis set and its values are listed in Table 8. The Mulliken atomic charge plot for T2CNH is shown in Figure 8. The C₉/C₃ atoms have the highest negative/positive charges, respectively among the other atoms in T2CNH due to the resonance.

Atoms	Charges	Atoms	Charges	Atoms	Charges
S1	-0.6516	H10	0.1263	N19	-0.0124
C2	0.2759	N11	0.1794	H20	0.1758
C3	1.9917	N12	-0.0550	C21	-0.0964
C4	-1.2036	H13	0.2477	H22	0.2280
C5	0.4451	C14	-0.7857	C23	-0.3517
H6	0.2687	O15	-0.2925	H24	0.1897
H7	0.1582	C16	0.9920	H25	0.1903
H8	0.2452	C17	-0.5899
C9	-1.7721	C18	0.0967

Table 8: The Mulliken atomic charges of T₂CNH.

Figure 8: The Mulliken atomic charges of T₂CNH.

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Thermodynamical Properties

Several thermodynamic parameters have been calculated using DFT/B3LYP/ 6-311++G(d,p) basis set are listed in Table 9. The thermodynamic parameters viz, entropy (S⁰_m), enthalpy (ΔH⁰_m) and heat capacity at constant pressure (C⁰ _p,m) for T2CNH was calculated from the theoretical harmonic wavenumbers obtained from B3LYP/6-311++G(d,p) basis set in the range 100-1000 k and listed in Table 10. It is evident from the Table 10 that the thermodynamic parameters increase with rise of temperature due to the fact that the molecular vibrational intensities increase with temperature. The correlation equations between these thermodynamic parameters and temperature were fitted by parabolic formula and the regression coefficient is also given in the parabolic equation. The correlation relation between the thermodynamic parameters and temperature are as follows:

Parameters	B3LYP/6-311++G(d,p)
Total Energies	-1062.41677
Zero-point Energy	114.99338 (Kcal/Mol)
Rotational constants (GHZ)	1.78813
	0.15572
	0.14465
Entropy
Total	122.336
Translational	42.214
Rotational	33.345
Vibrational	46.777

Table 9: The calculated total energy (a.u), zero point vibrational energies (kcal/mol), rotational constants (GHz) and entropy (cal/mol K^-1) for T₂CNH.

T (K)	S (Jmol-1K-1)	Cp (Jmol-1K-1)	ddH (kJmol-1)
100	349.07	100	6.95
200	436.15	159.71	19.86
298.15	511.96	224.53	38.7
300	513.36	225.74	39.12
400	586.95	287.34	64.85
500	656.77	338.54	96.24
600	722.24	379.34	132.21
700	783.25	411.8	171.83
800	840.01	438.01	214.36
900	892.88	459.52	259.27
1000	942.25	477.43	306.15

Table 10: Thermodynamic properties of T₂CNH at different temperatures.

C⁰_p,m= 4.44266+0.01876T+1.6571 × 10^-5 T² (R²=0.99929)

S⁰ _m= 1.35549+0.00572T+5.0560 × 10^-5 T² (R²=0.99997)

ΔH⁰_m= 3.15466+0.01332T+1.1767 × 10^-5 T² (R²=0.99944)

The correlation graphs between various thermodynamic functions and temperature are graphically presented in Figure 9.

Figure 9: The thermodynamic properties of T₂CNH at different temperatures.

Conclusion

The complete vibrational analysis has been performed to using quantum chemical calculation at DFT method for the first time to the title molecule T₂CNH. The calculated bond parameters are good agreement with the related single crystal X-ray diffraction (XRD) data. In T₂CNH, the thiophene and hydrazone moieties are co-planar, which shows a good conjuction between p-orbitals of all atoms of thiophene and hydrazone moieties. The vibrational data of T2CNH are well supported by the harmonic and related literature values. The β0 value of T2CNH molecule is found to be 1.5861 × 10^-30 esu, which is four time greater thatn that of urea. The NBO result reflects the charge transfer with in the molecule and the maximum energy takes place during π-π* transition. The Homo-Lumo band gap was calculated about 4.025 eV, which leads the T₂CNH molecule to become less stable and more reactive. The recorded UV-Vis spectral values are agree well with calculated values. MEP surface predict the reactive sites for electrophilic and nucleophilic attack. In addition, Mulliken atomic charges, zero point energy and thermodynamic properties are also calculated.

References

1. The Encyclopœdia Britannica (1882), Nature 25: 313-315.
2. Molvi KI, Vasu KK, Yerande SG, Sudarsanam V, Haque N (2007) Syntheses of new tetrasubstituted thiophenes as novel anti-inflammatory agents. Euro J Medi Chem 42: 1049-1058.
3. Rai NS, Kalluraya B, Lingappa B, Shenoy S, Puranic VG (2008) Convenient access to 1,3,4-trisubstituted pyrazoles carrying 5-nitrothiophene moiety via 1,3-dipolar cycloaddition of sydnones with acetylenic ketones and their antimicrobial evaluation. Euro J Medi Chem 43: 1751-1720.
4. Ashalatha BV, Narayana B, Raj KKV, Kumari NS (2008) Synthesis of some new bioactive 3-amino-2-mercapto-5,6,7,8-tetrahydro[1]benzothieno[2,3-d]pyrimidin-4(3H)-one derivatives. Euro J Medi Chem 42: 719-728.
5. Polivka Z, Holubek J, Svatek E, Metys J, Protiva M (1984) Potential hypnotics and anxiolytics: Synthesis of 2-bromo-4-(2-chlorophenyl)-9-[4-(2-methoxyethyl)piperazino]-6H-thieno[3,2,4-triazolo[4,3-a]-1,4-diazepine and of some related compounds. Collect Czech Chem Commun 49: 621-623.
6. Noguchi H, Kitazumi K, Mori M, Shiba T (2004) Electroencephalographic Properties of Zaleplon, a Non-Benzodiazepine Sedative/Hypnotic, in Rats. J Pharm Sci 94: 246-251.
7. Kim S, Yoon JY (2004) Hydrazones in science and synthesis. Sci Synth 27: 671-722.
8. Brehme R, Enders D, Fernandez R, Lassaletta JM, Aldehyde N (2007) N-Dialkylhydrazones as Neutral Acyl Anion Equivalents: Umpolung of the Imine Reactivity. Eur J Org Chem 34: 5629-5660.
9. Belskaya NP, Dehaen W, Bakulev VA (2010) Synthesis and properties of hydrazones bearing amide, thioamide and amidine functions. Archive Org Chem 275-332.
10. Bhole RP, Bhusari KP (2009) Synthesis, antimycobacterial activity and 3-d qsar studies of some new derivatives of p-hydroxybenzohydrazide. QSAR Comb Sci 28: 1405-1417.
11. Loncle C, Brunel JM, Vidal N, Dherbomez M, Letourneux Y (2004) Synthesis and antifungal activity of cholesterol-hydrazone derivatives. Eur J MedChem 39: 1067-1071.
12. KK Bedia, Elcin O, Seda U, Fatma K, Nathaly S (2006) Synthesis and characterization of novel hydrazide–hydrazones and the study of their structure–antituberculosis activity. Eur J Med Chem 41: 1253-1261.
13. Subashchandrabose S, Meganathan C, Erdogdu Y, Saleem H, Jayakumar C (2013) Vibrational and conformational analysis on N1-N2-bis(pyridine-4-yl)methylene)benzene-1, 2-diamine. J Mol Struct 1042: 37-44.
14. Subramaninan N, Sundaraganesan N, Jayabharathi JA (2010) Molecular structure, spectroscopic (FT-IR, FT-Raman, NMR, UV) studies and first order molecular hyperpolarizabilities of 1,2-bis (3-methoxy-4-hydroxy benzlidene) hydrazine by density functional method. Spectrochim Acta A Mol Biomol Spectrosc 76: 259-269.
15. Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA, et al. (2004)Theoretical and Computational Aspects of Magnetic Organic Molecules. Gaussian Inc, Wallingford, CT.
16. Schlegel HB(1982) Optimization of equilibrium geometries and transition structures. J Comput Chem 3: 214-218.
17. Jamróz MH (2006)Vibrational modes of 2,6-, 2,7-, and 2,3-diisopropylnaphthalene, A DFT study.J Mol Struct 787: 172-183.
18. Michalska D(2003) Raint Program, Wroclaw University of Technology, Poland.
19. Michalska D, Wysokinski R(2005)The prediction of Raman spectra of platinum(II) anticancer drugs by density functional theory.Chem Phys Lett 403: 211-217.
20. Fleming GD, Koch R, Vallete MMC (2006) Theoretical study of the syn and anti thiophene-2-aldehyde conformers using density functional theory and normal coordinate analysis. Spectrochim Acta AMol Biomol Spectrosc65: 935-945.
21. Balachandran V, Janaki A, Nataraj A (2014) Theoretical investigations on molecular structure, vibrational spectra, HOMO, LUMO, NBO analysis and hyperpolarizability calculations of thiophene-2-carbohydrazide. Spectrochim Acta A Mol Biomol Spectrosc118: 321-330.
22. Unal A, Eren B (2013) FT-IR, dispersive Raman, NMR, DFT and antimicrobial activity studies on 2-(Thiophen-2-yl)-1H-benzo[d]imidazole. Spectrochim Acta AMol Biomol Spectrosc 114: 129-136.
23. Brathen O, Kveseth K, Nielsen CJ, Hagen K (1986) Molecular structure and conformational equilibrium of gaseous thiophene-2-aldehyde as studied by electron diffraction and microwave, infrared, Raman and matrix isolation spectroscopy. J Mol Struct 145: 45-68.
24. Geiger DK, Geiger HC, Williams L, Noll BC (2012) 2-(Thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1 H –benzimidazole. Acta Cryst E: Structure Reports Online 68: o420.
25. Rauhut G, Pulay P (1995) Transferable Scaling Factors for Density Functional Derived Vibrational Force Fields. J Phys Chem 99: 3093-3100.
26. Bellamy LJ (1980) The infrared spectra of complex molecules, vol 2 champman and Hall, London.
27. Babu NR, Subashchandrabose S, Padusha MSA, Saleem H, Manivannan V, et al.  (2014) Synthesis and structural characterization of (E)-N′-((Pyridin-2-yl) methylene) benzohydrazide by X-ray diffraction, FT-IR, FT-Raman and DFT methods. J Mol Struct 1072: 84-93.
28. Varsanyi G (1974) Assignments of vibrational spectra of 700 Benzene Derivatives, Wiley, New York.
29. Sathyanarayanan DN (2000) Vibrational spectroscopy theory and Applications, 446-447.
30. Varsanyi G (1973) Assignments for Vibrational Spectra of Seven Hundred Benzene derivatives, 1/2 Academic Kiaclo.
31. Jag M (2001) Organic Spectroscopy Principles and Application, (2nd edn), Narosa Publishing house, New Delhi.
32. Lorenc J (2012) Dimeric structure and hydrogen bonds in 2-N-ethylamino-5-metyl-4-nitro-pyridine studied by XRD, IR and Raman methods and DFT calculations. Vib Spectrosc 61: 112-123.
33. Krishnakumar V, Dheivamalar S, Xavier RJ, Balachandran V (2006) Analysis of vibrational spectra of 4-amino-2, 6-dichloropyridine and 2-chloro-3, 5-dinitropyridine based on density functional theory calculations. Spectrochim Acta A Mol Biomol Spectrosc65: 147-154.
34. Sundaraganesan N, Saleem H, Mohan S (2003) Vibrational spectra, assignments and normal coordinate analysis of 2-amino-5-bromopyridine.Spectrochim Acta A Mol Biomol Spectrosc59: 1113-1118.
35. Silverstein M, Basseller CG, Morill C (1981) Spectrometric identification of organic compound, Wiley; Network.
36. Badawi HM (2009) Structural stability, C–N internal rotations and vibrational spectral analysis of non-planar phenylurea and phenylthiourea. Spectrochim Acta A Mol Biomol Spectrosc72: 523-527.
37. James C, Ravikumar C, Sundius T, Krishnakumar V, Kesavamoorthy R, et al. (2008) FT-Raman and FTIR spectra, normal coordinate analysis and ab initio computations of (2-methylphenoxy) acetic acid dimer.Vib Spectrosc 47: 10-20.
38. Weinhold F, Landis CR (2005) Valency and bonding: a natural bond orbital donor-acceptor perspective. Cambridge University Press.
39. Ott JB, Boerio-Goates J (2000) Calculations from Statistical Thermodynamics.