View of MOLECULAR STRUCTURE AND VIBRATIONAL CHARACTERIZATION OF 2,6-DICHLORO-4 NITROANILINEUSING BY SPECTROSCOPIC AND COMPUTATIONAL TECHNIQUES

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Vol. 02, Issue 11,November 2017 Available Online: www.ajeee.co.in/index.php/AJEEE

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MOLECULAR STRUCTURE AND VIBRATIONAL CHARACTERIZATION OF 2,6- DICHLORO-4 NITROANILINEUSING BY SPECTROSCOPIC AND COMPUTATIONAL

TECHNIQUES Vishrut Chaudhary

Assistant Professor, Department of Chemistry, D. N. College, Meerut U P

Abstract - The vibrational spectra of 2,6-dichloro-4-nitroaniline were recorded in the regions 4000– 400 cm

^-1

and 3500–100 cm

^-1

, respectively. Also calculated the same vibrational spectra by theortical calculation by DFT methods. Utilizing the observed data, a complete vibrational assignment and analysis of the fundamental modes of the compounds was carried out. In this kind of systems, the position of the substituent group in the benzene ring as well as its electron donor– acceptor capabilities play a very important role on the molecular and electronic properties. The DFT calculations for the title compound were carried out by Gaussian 09 software package using B3LYP/6-311++G(d,p) basis sets . The influence of chlorine, amino and nitro group on the geometry of benzene and its normal modes of vibrations has also been discussed.

Keywords: 2,6-dichloro-4-nitroaniline, IR Spectra,Raman spectra, DFT, Gaussian 09 software.

1 INTRODUCTION

Aromatic amines are very important in biology and chemical industry.

Particularly aniline and its derivatives are used in the production of dyes, pesticides and antioxidants. Some of the para- substituted derivatives of aniline are local anaesthetics, and in these molecules amino group plays an important role in the interaction with corresponding receptor. The spectra of these molecules change to a large extent with polar and non-polar solvents. Secondly, the various substituents modify the vibrational frequencies, although the aromatic character is retained in all substituted aniline.The prototypical molecule, aniline, which is the simplest aromatic amine [1], and its derivatives were widely used to study the electronic structure [2-4], vibrational spectroscopic [5-11], and NLO properties [12-17] The enhanced interaction between the aromatic ring and the amino group induces variations in the molecular geometry of the aniline. The structural and the vibrational parameters of aniline can be modified by introduce ng substituent groups to its molecular structure[18].The normal modes of vibrations have significant role in molecular materials with large NLO activities. In some cases, the vibrational NLO property of materials is dominated over their electronic NLO responses [19].

The characteristic features of the vibrational spectra of halogen derivatives of anilines, particularly chlorine substituted anilines have been reported.

1.1 Experimental and Computational The infrared spectra of the compound 2,6- dichloro-4nitroaniline (further referred as 2,6DCl4NA) was recorded on Perkin- Elmer M-683 spectrophotometer in the region 400-4000 cm

^-1

using KBr pellets and nujolmull solvent. The laser Raman spectrum in the region 40-4300 cm

^-1

was recorded on “Spex Rama Lab”

spectrophotometer using 52 mg argon- krypton laser beam of wavelength 488 nm. Whereas All the calculations were carried out for the title compound with Gaussian 09W program package [20]using the Becke-3Lee-Yang-Parr (B3LYP) functional supplemented with the 6- 311++G (d,p) standard basis set further referred as DFT calculations. All the parameters were allowed to relax and all the calculations converged to an optimized geometry which corresponds to a true energy minimum, as revealed by the absence of imaginary values in the wave number calculations.

2 RESULTS AND DISCUSSION

Molecular Structure: The molecular

structure of the mentioned compound

2,4,6DNCAis shown in Figure 1. The

optimized bond lengths, bond angles and

dihedral angles of the compound is

calculated by B3LYP method using 6-

311++G (d,p) basis sets are listed in Table

1 is accordance with atom numbering

scheme as shown in Fig. 1. Since the

exact crystal structure of the compound

2,6DCl4NA is not available till now, the

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2 optimized structure can only be compared

with other similar system for which the crystal structures have been solved.

Figure 1: Optimized Geometry of.2, 6 DCl4NA

Table 1 Calculated Optimized Geometrical Parameters of 2,6DCl4NA: bond length (Å), bond angle(

^o

), dihedral angles(

^o

)

S.

No Atoms of

molecule Bond (Å)

length Angle between

atoms (^o) Bond angle

(^o) Dihedral angle between

atoms (^o) Dihedral angle (^o)

1. R(1,2) 1.4168 A(2,1,6) 116.0458 D(6,1,2,3) 0.3657

2. R(1,6) 1.4102 A(2,1,9) 121.8215 D(6,1,2,12) -179.5206

3. R(1,9) 1.3636 A(6,1,9) 122.1125 D(9,1,2,3) -178.0346

4. R(2,3) 1.3789 A(1,2,3) 122.7086 D(9,1,2,12) 2.0791

5. R(2,12) 1.7596 A(1,2,12) 118.1734 D(2,1,6,5) -0.3705

6. R(3,4) 1.3958 A(3,2,12) 119.1179 D(2,1,6,13) 179.533

7. R(3,7) 1.0808 A(2,3,4) 118.8417 D(9,1,6,5) 178.0247

8. R(4,5) 1.3906 A(2,3,7) 120.6716 D(9,1,6,13) -2.0718

9. R(4,14) 1.437 A(4,3,7) 120.4866 D(2,1,9,10) -168.5562

10. R(5,6) 1.3845 A(3,4,5) 120.8371 D(2,1,9,11) -13.2151

11. R(5,8) 1.082 A(3,4,14) 124.2379 D(6,1,9,10) 13.1406

12. R(6,13) 1.7584 A(5,4,14) 94.1826 D(6,1,9,11) 168.4817

13. R(9,10) 1.0066 A(4,5,6) 114.9249 D(1,2,3,4) -0.1229

14. R(9,11) 1.0066 A(4,5,8) 141.0334 D(1,2,3,7) 179.9659

15. R(14,15) 1.4376 A(6,5,8) 119.2798 D(12,2,3,4) 179.7624

16. R(14,16) 1.4377 A(1,6,5) 119.9271 D(12,2,3,7) -0.1448

17. A(1,6,13) 120.793 D(2,3,4,5) -0.1363

18. A(5,6,13) 122.2858 D(2,3,4,14) 179.9924

19. A(1,9,10) 118.5222 D(7,3,4,5) 179.775

20. A(1,9,11) 119.192 D(7,3,4,14) -0.0962

21. A(10,9,11) 117.7113 D(3,4,5,6) 0.1307

22. A(4,14,15) 111.2103 D(3,4,5,8) -179.7872

23. A(4,14,16) 117.8026 D(14,4,5,6) -179.9867

24. A(15,14,16) 60.9521 D(14,4,5,8) 0.0954

25. D(3,4,14,15) 32.8086

26. D(3,4,14,16) -0.0693

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27. D(5,4,14,15) -147.0695

28. D(5,4,14,16) -179.9177

29. D(4,5,6,1) 0.1352

30. D(4,5,6,13) -179.7677

31. D(8,5,6,1) -179.9477

32. D(8,5,6,13) 0.1494

Vibrational spectra; A detailed study of vibrational spectra has been carried out of the reported compound2,6DCl4NA and the vibrational frequencies have been calculated using DFT-B3LYP level with 6-311++G(d,p), there is a good agreement between the observed frequencies and those calculated by the DFT comparative chart is shown in Table 2 in which experimental values of IR (KBr and nuzol), and laser Raman are displayed and simultaneously compared with the calculated values.

Table 2

S.No. Experimental

Calculated Assignments

Raman IR

1 3685.5 3705 3740.5 α (N-H)

2 3370 3597.5 β (N-H)

3 3035 3085 γ (C-H)

4 3040 γ (C-H)

5 1615 1650 NH2 scissoring

6 1568 1609.5 γ (C-C)

7 1545 γ (C-C)

8 1535 α (NO2)

9 1510 1500.5 γ (C-C)

10 1440 1485 1450 γ (C-C)

11 1350 1350 1350.5 β (NO2)

12 1330 1332 γ (C-C)

13 1310 γ (C-C)

14 1290 1270 1250.5 γ (C-NH2)

15 1215 µ (C-H)

16 1140 1151 µ (C-H)

17 1065 1050 1083.5 NH2 twisting

18 1000 (C-C-C) bending

trigonal

19 950 935 ε (C-H)

20 890 ε(C-H)

21 855 NO2 scissoring

22 820 830.5 (C-C) ring

breathing

23 785 789.5 α (NH2)

24 750 750 750.5 γ (C-Cl)

25 725 725 NO2 wagging

26 715 711.5 γ (C-Cl)

27 605 591.5 µ (C-C)

28 570 590 NH2 wagging

29 540 540 539.5 NO2 rocking

30 365 360 355.5 µ (C-NH2)

31 235 229 α (CNH2)

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32 120 129.5 ε (C-Cl)

33 70 lattice vibration

34 50 59 lattice vibration

Where α = assymetric stretching, β = symmetric stretching, γ = stretching, µ = in-plane bending and ε is out of plane bending.

NH2. Group Vibrations; The aniline molecule is a non-planar molecule with NH

2

group inclined at 30° to the plane of benzene ring.The stretching, scissoring and the rocking modes of the aminogroup are expected in the regions 3700–3300 cm_1, 1700–1600 cm_1, and 1150–900 cm_1, respectively [21]In our present study the bands at 3685 cm

^-1

for Raman and the IR bands at 3705.5cm

^-1

and 3370 cm

^-1

represents stretching which very well correlate with the calculated values 3740.5 cm

^-1

and 3597.5 cm

^-1

, In case of scissoring the bands at IR 1615 cm

^-1

corresponding to calculated value 1650 cm

^-1

represents NH

2

scissoring similarly the IR band at 1140 cm

^-1

corresponding to calculated value of 1151 cm

^-1

shows the rocking mode.

NO

2

Group Vibrations ;This group absorb strongly at 1530-1500 cm

^-1

which is known as asymmetric nitro group and weakly at 1370-1330 cm

^-1

known as symmetric nitro group. [22-24] In this light the IR band at 1510 cm

^-

1

corresponding to the calculated value 1500.5 cm

^-1

and the Raman and IR bands at 1350 cm

^-1

corresponding to the calculated value 1350.5 cm

^-1

represents the above mentioned modes. In addition to these the nitro group usually have strong aromatic ring absorption at 760- 705 cm

^-1

which is visible at 725 cm

^-1

and its calculated counterpart at 750.5 cm

^-1

. 3 BENZENE RING VIBRATIONS

C-C vibrations: The 1,3,5-tri substituted benzene derivatives show the peaks due to the in-plane C-C stretching vibrations in the wave number region 1630–1550 cm

^-1

[21] the IR band at 1568 cm

^-1

corresponding to calculated value of 1600 cm

^-1

represents this mode. The vibrational pair of CC stretching in 1,3,5- trisubstituted benzene is found to be in the region 1480–1400 cm_1 [21]. The strong peaks observed in the Raman at

1440 cm

^-1

and IR 1485 cm

^-1

and the calculated value 1450 cm

^-1

exhibits this mode. The wavenumber of the CC stretching vibration (Kekulemode) of 1,3,5 tri-substituted benzene is expected in the region 1300–1200 cm

^-1

[21] which is shown in Raman band at 1290 cm

^-1

and IR band at 1270 cm

^-1

corresponding to the calculated value of 1250.5 cm

^-1

C-H vibrations; The heteroaromatic system shows the C-H stretching absorption bands in the region 3100–

3000 cm

^-1

[25]. The bond stretching modes of the unperturbed C-H bonds of 2,4,6DNCA are identified from the sharp peaks at 3035 cm

^-1

and 3085 cm

^-1

in the Raman and IR spectrum respectively C-Cl vibrations the C-Cl stretching vibrations usually give strong peaks in the spectral region 710–505 cm

^-1

in our study the IR band at 715 cm

^-1

corresponding to the calculated value of 711.5 cm

^-1

shows this mode.

Figure 2: Calculated IR Spectrum of 2, 6-Dichloro-4-Nitroaniline using by

Gaussain 09W program package,

B3LYP.

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2 Figure 3 Calculated Raman Spectrum of

2, 6-Dichloro-4-Nitroaniline using by Gaussian 09W program package,

B3LYP.

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