Spectral and conformational studies on 3-pyridinealdazine by DFT approach

Accepted Manuscript Spectral and conformational studies on 3-pyridinealdazine by DFT approach R. Arulmani, R. Balachander, P. Vijaya, K.R. Sankaran PII: DOI: Reference:

S1386-1425(14)01768-5 http://dx.doi.org/10.1016/j.saa.2014.12.006 SAA 13038

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

29 March 2014 16 July 2014 1 December 2014

Please cite this article as: R. Arulmani, R. Balachander, P. Vijaya, K.R. Sankaran, Spectral and conformational studies on 3-pyridinealdazine by DFT approach, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.12.006

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Spectral and conformational studies on 3-pyridinealdazine by DFT approach R. Arulmania, R. Balachanderb, P. Vijayaa, K.R. Sankarana* a

Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamilnadu, India

b

Department of Chemistry, Achariya College of Engineering Technology, Villianur 605 110, Puducherry, India

*Corresponding author Dr. K.R. Sankaran Professor Department of Chemistry Annamalai University Annamalainagar 608 002 Tamil Nadu, India. Tel.: +91 4144 238601 Fax: +91 4144 238145 E-mail: [email protected]

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Spectral and conformational studies on 3-pyridinealdazine by DFT approach R. Arulmania, R. Balachanderb, P. Vijayaa, K.R. Sankarana* a

Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamilnadu, India

b

Department of Chemistry, Achariya College of Engineering Technology, Villianur 605 110, Puducherry, India ABSTRACT 3-Pyridinealdazine was synthesized and characterized by FT-IR, 1 H,

13

C NMR and

Mass spectroscopy. The conformations of azine was determined theoretically besides selected geometrical parameters, HOMO-LUMO energies, polarizability, hyperpolarizability, natural bond orbital (NBO), atomic charges, Mulliken charges and atom in molecule (AIM) analysis were also calculated. The optimized geometry of the symmetrical azine, HOMO-LUMO and molecular electrostatic potential (MEP) surface were also evaluated using B3LYP/6-31G(d,p) basis set. 13C NMR data were also computed using Gaussian-03 package and compared with the observed values according to density functional theory (DFT) method and analyzed. Keywords: Computational; Spectral; Conformational; 3-Pyridinealdazine 1. Introduction Hydrazines and their derivatives constitute an important classes of compounds that has found wide utility in organic synthesis [1–2]. The chemistry of carbon nitrogen double bond of hydrazone is becoming the backbone of condensation reaction in benzo-fused Nheterocycles [3] also it constitutes an important class of compounds for new drug development [4]. A number of heterocyclic compounds have been shown to possess pharmacological activities [5–7]. Azines, R1R2C=N–N=CR1R2, have achieved great significance in organic synthesis [8–12]. The ability of azines derived from 2-

3

pyridinecarboxaldehyde as polydentate ligand to form very stable complexes with different cations is well known [13]. Azines have been used extensively as ligands for the synthesis of novel organometallic compounds [14–16]. Inspite of these synthetic utility, azines have good electronic, linear and non-linear optical properties [17–20]. Several theoretical analysis have been carried out for isomeric forms of these azines [21–24]. Azines are useful for the isolation, purification and characterization of carbonyl compounds [25]. Recently we have synthesized and determined the conformations of some 4-biphenylcarboxaldehydes by theoretical methods and spectral studies [26]. Thus, the present investigation focused on the synthesized and theoretical investigation of the molecular structure, charges, NBO and analysis of 3-pyridinealdazine. HOMO-LUMO energies, dipole moment, polarizability and first hyperpolaraizability were also determined by DFT method and analyzed. 2. Experimental details 2.1. Spectral measurements The IR spectrum was recorded at room temperature on Nicolet Avatar 330 FT-IR spectrometer. The sample has been mixed with KBr and the pellet technique is adopted to record the spectra. The mass spectrum was performed using Varian Saturn 2200 GC-MS spectrometer. The 1 H (400 MHz) and

13

C NMR (100 MHz) spectra were recorded at room

temperature on Bruker 400 MHz instrument using 10 mm sample tube. Samples were prepared by dissolving about 10 mg of the sample 2.5 mL of chloroform-d containing 1% TMS for

13

C. The 1H-1 H and 1H-13C COSY spectra analysis were also performed on a

Bruker 400 NMR spectrometer.

4

2.2. NLO technique In order to confirm the second order nonliner optical properties of the material, the second harmonic generation (SHG) test on the powder sample of a representative azine was performed by Kurtz and Perry powder SHG method [27]. A Q-switched Nd:YAG laser wavelength 1064 nm was used with input radiation 2.2 mJ/pulse. A small portion of the azine was powdered to a uniform particle size and then packed in a capillary of uniform bore and exposed to laser radiations. The output from the sample was monochromated to collect only the second harmonic (532 nm) and the intensity was measured using a photomultiplier tube. 2.3. Preparation of symmetrical azine 2-Pyridinealdazine was first prepared by Lenart [28]. The 2-pyridinecarboxaldehyde used in the present work was obtained from the Aldrich chemical company and used without further purification. About 0.04 mol of 2-pyridinecarboxaldehyde and 0.02 mol of hydrazine monohydrate was taken in a round bottom flask. The reaction mixture dissolved in ethanol and refluxed well for one hour. The reaction mixture was kept at room temperature for an hour. The separated solid was filtered and purified by recrystallization from ethanol. 2.4. Computational details All calculations were done at density functional theory (DFT) level on a personal computer using Gaussian-03 package using B3LYP/6-31G(d,p) basis set [29]. The polarizabilites and hyperpolarizabilities were determined from the DFT optimized structure by finite field approach using B3LYP/6-31G* basis set. The topological properties of the electronic charge density have also characterized using AIM-All software package. NBO calculations using the B3LYP/6-31G(d,p) available in Gaussian-03 and AIM calculations were done using AIM-All software package [30]. Mulliken charges were also calculated using same Gaussian-03 package.

5

3. Results and discussion 3-Pyridinealdazine was synthesized as shown in Scheme1 and characterized by IR, 1

H,

13

C, 1 H-1 H and 1 H-13 C COSY spectra. The labelling of the atoms followed in the

present study was indicated in the Scheme1. 3.1. Spectral studies of 3-pyridinealdazine 3.1.1. IR spectral studies The sharp peak around 1626 cm–1 in the IR spectrum are exhibited for νC=N mode (Fig. S1). Another sharp peak observed at 1040 cm–1 it was assigned νN–N stretching vibration. The aromatic ν C–H stretching vibration appeared at 3052 cm–1 and aliphatic νC–H stretching vibration were seen around 2922 cm–1, respectively. The mass spectrum was observed with molecular weight of molecular ion peak [M+1] = 211 (Fig. S2). The corresponding spectral assignments were listed in Table 1. 3.1.2. NMR spectral analysis The signals in the 1 H NMR spectra were assigned based on their positions, integrals and multiplicities and confirmed by the correlation observed in the 1 H-1H COSY spectrum. Two sharp singlets exhibit at 8.72 and 8.70 ppm are assigned to H(4) and H(5) azomethine proton and pyridine ring proton. A doublet centered at 8.12 ppm is corresponding to H(8) proton. The two triplets exhibit at 7.80 and 7.36 ppm could be assigned to pyridine ring proton of H(7) and H(6) it was ortho and meta with respect to nitrogen atoms. The 1H NMR spectrum of 3-pyridinealdazine is shown in Fig. S3. This assignment is further confirmed by the correlations observed in the 1H-1 H COSY spectrum is shown in Fig. 1. The assignment signals in the 13C NMR spectrum pyridine moiety is attached to linear chain linked in symmetrical azine. The high frequency signal observed at 162.1 ppm is due to C=N group. A low intense signal (ipso carbon) observed at 152.8 ppm is

6

corresponding to carbon C(2). The high intense signal at 149.9 ppm is due to ortho with respect to nitrogen atom N(4). The remaining signals at 136.6, 125.1 and 122.5 ppm are due to meta and para proton of pyridine ring at C(8), C(7) and C(6) carbons, respectively. The 13 C NMR spectrum of 3-pyridinealdazine is shown in Fig. S4. This assignment was further confirmed by 1 H-13 C COSY spectrum as shown in Fig. 2. The 1 H and 13C NMR chemical shifts values were listed in Table 2. 3.2. Conformational analysis There are two possible conformations for the title compound as shown in Fig. 3. The two pyridine moiety E configuration in conformation A and Z configuration in conformation B. In order to confirm the favoured conformation computational calculations were performed according to DFT method using B3LYP/6-31G(d,p) basis set available in Gaussian-03 package and the relative energies determined are found to be –1791288.469 (A) and –1791306.3489 kJ mol–1 (B). Thus, the theoretical study predicts the favoured conformation as B (Z configuration) only. In conformation B the two pyridine moieties are opposite to each other, whereas in confirmation A the two pyridine moieties are on the same side. The possibility existing in conformation A is ruled out. Because, severe steric crowding exists between the two pyridine moieties. Among the two conformers, conformer B was found to be the stable conformer. 3.3. Geometrical parameters From the optimized structure of geometrical parameters were derived by DFT method as shown in Fig. 4. The observed torsional angles were C2–N1–N1′–C2′ (0.045°), C8–C3–C2–N1 (0.024°) and N4′–C3′–C8′–C7′ (–0.005°) in azine indicate that the pyridine ring moiety is slightly distorted from the plane containing –C=N–N=C–. It may be expected to be NLO active. Remaining torsional angles were found to be –179.990 and 179.998°, respectively. These values were listed in Table S1.

7

3.4. NBO analysis NBO analysis at B3LYP/6-31G(d,p) level was carried out for the azine and important second order perturbative estimates of donor-acceptor interactions are displayed. The occupancies and the energies of the orbitals involved in primary delocalization are also reported in Table 3. The interactions between filled and empty NBO’s can be described as a hyperconjugative electron transfer process from the donor (filled) to the acceptor (vacant) orbital and the energy lowering due to this interaction is expressed as E2. The delocalization energies corresponding to the transfer of π-electrons from C7–C8 to C3–N4, C3–N4 to C5–C6, C5–C6 to C7–C8, C7′–C8′ to N4′–C3′, C6′–C5′ to C7′–C8′ and N4′–C3′ to C6′–C5′ bonds are found to be acceptable above 20 kcal mol–1. The lone pair of electrons available on nitrogen’s N1, N1′, N4 and N4′ are delocalized on the antibonding orbitals of C2′–H2′, C2–H2, C8–C3 and C3′–C8′ bonds. This indicates that there may be the presence of two H-bonds between N1⋅⋅⋅H2 and N1′⋅⋅⋅H2′ with low E2 values. 3.5. AIM analysis The AIM theory is a useful tool in the interpretation of the charge density in a wide variety of chemical concepts. The electron density of molecular system defines atom and bonds. We have calculated at DFT level the charge density ρ(r) Laplacian of ρ(r) [∇2ρ(r)] and ellipticity (ε) at the position of the bond critical point (BCP) and charge density of the ring critical point (RCP) in azine results are gathered in Table 4. Atom in molecules electron density topological analysis revealed the existence of 27 BCP with a (3, –1) topology between the atoms connected by covalent bond. The negative values obtained for the Laplacian are clearly indication that the corresponding bonds are covalent bonds. RCP of pyridine moiety are slightly having high electron density in the azine. The AIM analysis revealed that there is no intramolecular hydrogen found in the molecule.

8

3.6. HOMO-LUMO energies HOMO-LUMO energies, electronic dipole moment, polarizabilities and hyperpolarizabilities were also derived and the values are listed in Table 5. The HOMO-LUMO plots are given in Fig. 5. The HOMO orbital is mainly derived from pz orbitals of carbon and nitrogen atoms except those of C7 and C7′ do not participate in HOMO orbital. The formation of LUMO orbital does not involve the participation of pz orbitals of carbons C5 and C2′ alone. The HOMO-LUMO energy gap of azine was calculated at the B3LYP/6-31G(d,p) level reveals that the energy gap reflect the chemical activity of the molecule. HOMO energy = –6.336 eV, LUMO energy = –2.189 eV. The band gap between HOMO and LUMO orbital energy is found to be 4.147 eV. 3.7. NLO analysis NLO can be well explained by the polarizability analysis of the azine using DFT method [B3LYP/6-31G(d,p)]. The dipole moment (µ), the polarizability (α0) and first hyperpolarizability (βtot) are related directly to the nonlinear optical efficiency of structures. The calculated value of αi,j, βijk are converted into electrostatic units from atomic units (α: 1 a.u = 0.1482 × 10 –24 esu; β : 1 a.u = 8.6393 × 10–33 esu) [31]. The total static dipole moment ‘µ’ is defined as

µ = (µ x2 + µ y2 + µ z2 )

1/2

… (1)

The mean polarizability < α> has been evaluated using the formula

<α >=

1 (α xx + α yy + α zz ) 3

… (2)

The first hyperpolarizability βtot is given by

[

β tot = (β xxx + β xyy + β xzz ) + (β yyy + β yzz + β yxx ) + (β zzz + β zxx + β zyy ) 2

2

]

2 1/2

… (3)

9

The µ value of 3-pyridinealdazine is found to be 0.0759 Debye. In the azine are found to be polar molecules having non-zero dipole moment components. It has a β total value 1495.57 esu. The band gap of azine is found to be 4.147 eV which is greater than the band gap of the NLO active molecules. Hence a least NLO activity is explained for 3-pyridinealdazine. This is evidenced by second harmonic generation (SHG) test. The experimental studies revealed that the 3-pyridinealdazine molecule is NLO inactive in nature. 3.8. MEP surfaces

Three dimensional distribution of MEP is highly useful in predicting the reactive behaviour of the molecule. The MEP surface is on overlaying of the electrostatic potential on to the isoelectron density surface. This is a valuable tool for describing overall molecule charge distribution as well as anticipating sites of electrophilic addition. In the azine region of negative charges (red colour) is seen around the electronegative nitrogens N1 and N1′ are susceptible for electrophilic attack. Blue colour represents strongly positive region and the predominant green region in the MEP surfaces corresponds to a potential halfway between the two extremes red and blue region in azine. The MEP surface picture of the azine are given in Fig. 6. 3.9. Molecular properties 3.9.1. Experimental and theoretical 1H and 13C NMR spectral analysis

The 1H and 13C NMR chemical shifts were also determined theoretically calculations of the symmetrical azine was made in CDCl3 [SCRF = (solvent = chloroform)] by using B3LYP/6-31G(d,p) basis set. The 1 H and 13C chemical shifts relative to reference TMS are determined from shielding tensors using the scaling factor 31.8821 and 182.4656, respectively. The experimental 13C chemical shifts are closer to the theoretical values and correlations between experimental and theoretical

13

C values are indicated in Fig. S5.

Theoretically determined 1 H chemical shifts are generally higher when compared to experimental values. The 1 H and 13 C chemical shifts values are listed in Table S2.

10

3.9.2. Charges

Charges calculated from NBO calculations (B3LYP/6-31G(d,p)) as basis set (Table S3). From Table S3 it is inferred that all hydrogens and sp2 carbons attached to electronegative atoms such as nitrogen (C2′, C2 and C5) alone attain positive charge. However for sp3 hybridized carbons attached to hydrogen atoms attain the negative charges in this NBO method. 4. Conclusions

In this work 3-pyridinealdazine was synthesized and characterized by FT-IR, 1 H, 13C NMR and mass spectral studies. The Gaussian-03 B3LYP/6-31G(d,p) calculations on the azine are used to evaluate the conformational analysis of the two possible conformers, to identify Z configuration in conformation B, the stable conformation, to determine the dipole moment, polarizability, hyperpolarizability, bond lengths, bond angles and torsional angles, MEP surface, HOMO-LUMO energies, natural and Mulliken charges were theoretically derived. The NLO behaviour analysis of 3-pyridinealdazine has been studied experimentally by SHG test. It reveals that the molecule was NLO inactive in nature. In this study, AIM analysis reveals that there is no intramolecular hydrogen bonding in the azine. The theoretical 1H and 13C NMR chemical shift values calculated for 3-pyridinealdazine were also in good agreement with the experimental values. Supplementary data

Selected geometrical parameters, experimental and theoretical

1

H and

13

C

chemical shifts, Mulliken and Natural charges (Tables S1–S3); IR, mass, 1 H and 13

C NMR spectra and correlation between the experimental and theoretical

13

C chemical

shifts (Figs. S1–S5) for 3-pyridinealdazine are provided. Acknowledgement

The authors thank the Department of Chemistry, Annamalai University for recording all the spectra.

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R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C. Gonzalez, M. Head-Gordon, E.S. Replogle, J.A. Pople, Gaussian 98, Revision A.9, Gaussian, Inc., Pittsburgh, PA, 1998. [30] T.A. Keith, AIM-All (Version 11.04.03), (aim.tkgriskmill.com), 2011. [31] N. Sundaraganesan, E. Kavitha, S. Sebastian, J.P. Cornard, M. Martel, Spectrochim. Acta A 74 (2009) 788–797.

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Captions for scheme and figures Scheme 1. Synthetic route of 3-pyridinealdazine. Fig. 1. 1H-1H COSY spectrum of 3-pyridinealdazine. Fig. 2. 1H-13C COSY spectrum of 3-pyridinealdazine. Fig. 3. Two possible conformations for 3-pyridinealdazine. Fig. 4. Optimized geometry of the most favourable conformation for 3-pyridinealdazine. Fig. 5. HOMO-LUMO pictures of the stable conformer for 3-pyridinealdazine. Fig. 6. Molecular electrostatic potential (MEP) diagram for 3-pyridinealdazine.

15

Table 1 IR and mass spectral data of 3-pyridinealdazine. Assignments

Observed values (cm–1)

Mass analysis (m/z)

νC=N

1626

νN–N

1483

[M+1] = 211 (molecular ion peak)

Aliphatic C–H stretching Aromatic C–H out of plane bending vibration

1040 2922

16

Table 2 1 H and 13C NMR chemical shifts (ppm) of 3-pyridinealdazine. 1

13

H Chemical shift

C Chemical shift

H(4) and H(4′)

8.72

C(2) and C(2′)

162.1

H(5) and H(5′)

8.70

C(3) and C(3′)

152.8

H(8) and H(8′)

8.12

C(5) and C(5′)

149.9

H(7) and H(7′)

7.80

C(8) and C(8′)

136.6

H(6) and H(6′)

7.36

C(7) and C(7′)

122.5

C(6) and C(6′)

125.1

17

Table 3 NBO analysis for 3-pyridinealdazine. Donor

Acceptor

E2 (kcal mol–1)

BD(2)N1–C2

BD*(2)N1′–C2′

12.84

BD(2)N1–C2

BD*(2)C3–N4

10.46

BD(2)N1′–C2′

BD*(2)N1–C2

12.84

BD(2)N1′–C2′

BD*(2)N4′–C3′

10.46

BD(2)C7–C8

BD*(2)C3–N4

26.49

BD(2)C7–C8

BD*(2)C5–C6

18.33

BD(2)C3–N4

BD*(2)N1–C2

13.27

BD(2)C3–N4

BD*(2)C7–C8

13.31

BD(2)C3–N4

BD*(2)C5–C6

26.39

BD(2)C5–C6

BD*(2)C7–C8

20.33

BD(2)C5–C6

BD*(2)C3–N4

17.58

BD(2)C7′–C8′

BD*(2)C6′–C5′

18.33

BD(2)C7′–C8′

BD*(2)N4′–C3′

26.49

BD(2)C6′–C5′

BD*(2)C7′–C8′

20.33

BD(2)C6′–C5′

BD*(2)N4′–C3′

17.58

BD(2)N4′–C3′

BD*(2)N1′–C2′

13.27

BD(2)N4′–C3′

BD*(2)C7′–C8′

13.30

BD(2)N4′–C3′

BD*C6′–C5′

26.39

LP(1)N1

BD*(1)C2–H2

9.43

LP(1)N1′

BD*(1)C2′–H2′

9.43

LP(1)N4

BD*(1)C8–C3

10.32

LP(1)N4

BD*(1)C5–C6

9.66

LP(1)N4′

BD*(1)C3′–C8′

10.33

18

Table 4 AIM analysis of 3-pyridinealdazine. Bond

ρ

∇2ρ

ε

N1–N1′

0.3033

–0.4023

0.0067

C2′–N1′

0.3599

–0.9499

0.0482

C3′–C2′

0.2624

–0.5789

0.0467

N1–C2

0.3599

–0.9498

0.0482

C2–C3

0.2624

–0.5789

0.0467

C7–C6

0.2939

–0.7061

0.1188

C8–C3

0.2911

–0.6820

0.1314

H8–C8

0.2674

–0.8334

0.0013

H7–C7

0.2651

–0.8057

0.0094

C8–C7

0.2976

–0.7258

0.1197

C3–N4

0.3185

–0.9651

0.0572

N4–C5

0.3223

–0.9588

0.0276

C6–C5

0.2952

–0.7052

0.1361

C6–H6

0.2642

–0.7966

0.0017

C6′–C7′

0.2939

–0.7061

0.1188

C5′–C6′

0.2953

–0.7052

0.1361

C5′–N4′

0.3223

–0.9588

0.0276

H5′–C5′

0.2671

–0.8188

0.0113

N4′–C3′

0.3185

–0.9652

0.0572

H6′–C6′

0.2642

–0.7966

0.0017

C8′–H8′

0.2674

–0.8334

0.0013

C7′–H7′

0.2651

–0.8057

0.0094

C7′–C8′

0.2976

–0.7258

0.1197

H2′–C2′

0.2664

–0.8337

0.0005

C2′–H2′

0.2664

–0.8337

0.0005

Ring critical point Bond

ρ

C7–C8–C3–N4–C5–C6

0.0219

C7′–C8′–C3′–N4′–C5′–C6′

0.0219

19

Table 5 HOMO-LUMO energy (eV), dipole moment µ (D), polarizability (ρ) and hyperpolarizability of 3-pyridinealdazine. HOMO

LUMO

–6.336 Polarizability

–2.189

αxx αxy αyy αxz αyz αzz αtot (esu) × 10–24

52.867 1.241 21.318 5.682 –0.0898 7.6319 24.27

α = 1 a.u = 0.1482*10–24 esu. β = 1 a.u = 8.6393*10–33 esu.

Dipole moment ∆E µx 4.147 0.0215 Hyperpolarizability 5.698 βxxx –6.036 βxxy 21.925 βxyy 31.893 βyyy –5.236 βxxz –4.000 βxyz –5.426 βyyz 2.405 βxzz 12.024 βyzz –14.921 βzzz βtot (esu) × 10–33 1495.5790

µy

µz

µtotal

0.3657

0.1327

0.0759

20

Scheme 1

21

Fig. 1

22

Fig. 2

23

Fig. 3

24

Fig. 4

25

Fig. 5

26

Fig. 6

27

Research Highlights


3-Pyridinealdazine was synthesized and characterized by IR, 1 H, 13C NMR and mass spectroscopy.




Computational technique were carried out by B3LYP/6-31G(d,p) basis set.




Optimized geometry, HOMO-LUMO, MEP, polarizability, NBO and AIM analysis were discussed.




The AIM analysis revealed that there is no intramolecular hydrogen bonding found in the molecule.




1

H and 13C NMR chemical shifts have been compared with experimental values.

28

Graphical Abstract

Spectral and conformational studies on 3-pyridinealdazine by DFT approach R. Arulmania, R. Balachanderb, P. Vijayaa, K.R. Sankarana* a b

Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamilnadu, India

Department of Chemistry, Achariya College of Engineering Technology, Villianur 605 110, Puducherry, India