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Vol. 05,Special Issue 02, (IC-IRSHEM-2020) February 2020, Available Online: www.ajeee.co.in/index.php/AJEEE

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SPECTRAL STUDY OF SUBSTITUTED PYRIDINE

1Vipin Kumar & ²Subhash Chandra

1,2Department of Physics, SKD University, Hanumangarh (INDIA)

Abstract:- The N-heterocyclic molecules like pyridine, pyrimidine, cytosine, uracil etc.

and their derivatives are of the considerable antifungal, antibacterial, biological and pharmaceutical importance. Recent spectroscopic studies on these compounds have been motivated because the vibrational spectra of these free base molecules are very useful for understanding biological processes and in the analysis of relatively complex system.

Also pyridine derivatives like amino pyridines and marcapto pyridine etc. are widely used as drugs in certain diseases. Pyridine and its derivatives are extensively used as a solvent and as a synthetic intermediate in analytical chemistry. In view of this discussion, laser Raman (100-4000 cm^–1) and infrared (400-4000 cm^–1) of 2-chloro-6-ethoxy-3-nitro pyridine have been recorded and analyzed. The band obtained are discussed assuming the molecule under Cs point group symmetry.

1. INTRODUCTION

TheN-heterocyclic moleculeslikepyridine, pyrimidine, cytosine, uracil etc. and their derivatives are of the considerable antifungal, antibacterial, biological and pharmaceutical importance. Recent spectroscopic studies on these compounds have been motivated because thevibrational spectra of these free base molecules are very useful for understanding biological processes and in the analysis of relatively complex system. Along the macromolecular double helix chain, the vibrational modes of each base interactwith other bases through hydrogen bonding and these interactions affects the ring vibrations.

Pyridine molecules and their derivatives are the constituents of DNA and RNA and hence plays a central role in the structure and properties of the nucleic acids.

Also pyridine derivatives like amino pyridines and marcaptopyridine etc. are widely used as drugs in certain diseases [1]. Also, thealkaloids of pyridine group such as nicotine, cocaine, atropine, coniine etc. represents the simplest natural heterocyclic compounds having most useful chemical application as a drugs in several diseases and in animal metabolism. Pyridine and its derivatives are extensively used as a solvent and as a synthetic intermediatein analytical chemistry. So, the knowledge of the molecular structure, physio- chemical properties and vibrational studies of pyridine and its derivatives arehelpful for better understanding of their functions in several biological processes and analysis of the complex systems.

Jesson et al [2] have shown that the pyridine molecule has planar structure in the ground state and a quasi planner one in the excited state. Corsin et al [3], were the first who investigated the IR Raman IR Raman spectra of pyridine partially. Mc Cullough et al [4]

also studies the IR and Raman spectra of pyridine along with the calculation of statistical thermodynamic functions. Some workers [5-6] were the first who investigated the IR and Raman spectra of pyridine completely. Kaya et al [7] have studied the Raman spectra and electronic absorption spectra of pyridine and its non-luminescent behaviour. Furthermore, the IR and laser Raman spectra of pyridine and its derivatives have also been studied by several investigators [8-12].

The spectra of such molecules with substituents such as C2H5 of becomes more complicated due to change in the mechanical coupling [13-14]but becomes interesting as the group give rise to two types of interesting as the group give rise to two types of internal rotation (i) a rotation of the C2H5 group about Caryl -O axis (ii) the rotation of C2H5 group about C-C elthyl axis considerable efforts have been made towards the understanding of the vibrational spectra of the compound having C2H5 group, in terms of satirichindrance and conjugation [15-16].

1.2 Experrimental

The laser Raman spectra of 2-chloro-6-ethoxy-3-nitro pyridine (hereafter abbreviated as 2,6,3-CENP) molecule was recorded on Spex Raman lab Spectrophotometer using 52MW Argon Krypton laser beam of wavelength 488 nm. The infrared spectra of said compound

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was recorded on perkinElmer Spectrophotometer model-52 in the region 400-4000 cm–1 using KBr pellets technique.

2. RESULTS AND DISCUSION

The molecular structure of 2-chloro-6-ethoxy-3-nitro pyridine is given in Figure1. The infrared spectra of 2,6,3-CENP in KBr pellets is given in Figure 2. The laser Raman spectra of 2,6,3-CENP is given in Figure 3.

The fundamental vibrational frequencies of said molecule along with the assignments are given Table 1. The Cs point group symmetry has been assumed for the said molecule.

Figure 1 MOLECULAR STRUCTURE OF 2,6,3-CENP

Figure 2INFRARED SPECTRA OF 2,6,3-CENP IN KBr PELLETS

Figure 3 THE LASER RAMAN SPECTRA OF 2,6,3-CENP

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3 3. VIBRATIONAL SPECTRA

3.1 RING VIBRATIONS 3.1.1 C-H VIBRATION

The C-H stretching vibrations in pyridine and their derivatives lie in the range of 3000-3100 cm^–1 [17-18]. As the said molecule is a trisubstituted pyridine therefore two (C-H) stretching vibrations are expected in the said region. In the present investigation, the IR bands observed at 3057 cm–1 (in KBr) with Raman counterpart at 3060 cm–1 and Raman band at 3103 cm–1 have been assignment with the literature value [19]. The (C-H) in-plane and out- of-plane bending modes lie in the range of 1000-1250 cm–1 and 700-900 cm–1 respectively [18]. Some workers [20] assigned these modes at 1140, 1215 cm–1 and 890, 950 cm–1 in 2,6,-dichloro-4-nitro aniline. In view of these assignments the Raman band at 1158 cm–1 and IRband at 1189 cm–1 (KBr) with counterpart Raman value at 1182 cm–1 have been assigned to C-H in-plane bending modes while the Raman band observed at 871 cm–1 and IR band at 917 cm–1 (in KBr) with the counterpart Raman band at 921 cm–1 have been assigned to (C-H) out-of-plane bending modes respectively in 2,6,3-CENP.

3.1.2 C-C VIBRATIONS

In pyridine and their derivatives, the ring breathing mode has been assigned in the region 690–844 cm–1 [17, 18, 21]. In the present study, this band is identified at 756 cm–1 in Raman spectrum. The ring stretching, in-plane and out-of-plane bending modes are assigned in their respective regions [17-21] as given Table 1.

3.1.3 C-N VIBRATIONS

Bellamy [17] has suggested the ring stretching vibrations lie in the region 1600-1400 cm–1.

Some Workers [5] assigned (C-N) stretching vibrations at 1310 cm–1 in substituted pyridine while Hussain et al [12] assigned this mode at 1366 cm–1 in case of 2-chloro pyridine In view of these assignments the band observed at 1407 cm–1 in Raman spectrum has been assigned to (C-N) stretching mode [22].

3.1.4 C-X VIBRATIONS

Some workers [23] have assigned (C-NO2) streching vibrations mode at 1263 cm–1 in infrared spectrum in 2-chloro-3-nitro pyridine. In view of this assignment, the (C-NO2) streching mode has been assigned at 1267 cm–1 in Raman spectrum which is in accordance with literature value [17]. Goel et al [24] have assigned (C-Cl) stretching mode at 1065 and1055 cm–1 in 3-amino-2-chloro pyridine and in 5-chloro-2, 4-dimethoxy aniline.

In view of these assignments, the band observed at 1098 cm–1 in Raman spectrum has been taken to represents (C-Cl) streching mode in 2,6,3-CENP, Goel et [22] have assigend (C-Cl) (C-Cl) in-plane and out-of-plane bending vibrations in 2-amino-4-chloro-6- methyl pyrimidine at 332 cm–1 and 134 cm–1 respectively. In view of this assignment, the Raman band observed at 333 cm–1 and 192 cm–1 has been assigned to (C-Cl) in-plane and out-of-plane bending mode respectively in the present molecule.

Some workers [17,18] has assigned (Caryl–O) stretching vibration mode between 1260 and 1244 cm–1 in various monohalogenated anisoles. Goel et al [24] have assigned this mode at 1282 and 1236 cm–1 in pyridine and at 1244 and 1202 cm–1 in pyrimidine. In view of these assignments, this mode has been identified at 1249 cm–1 in Raman spectrum in the present molecule. This also find support from the literature [18]. Yadav et al [23] have

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assigned (C-OC2H5) in-plane bending mode at 535 and 519 cm–1 in 2-hydorxy-3-methoxy benzaldehyde semicarbazone.

In view of this assignment the IR band at 522 cm–1 (in KBr with counterpart Raman band at 519 cm–1 has been identified to this mode. This also in accordance with the literature [17]. Some workers [18] have assigned (C-O2H5) out-of-plane bending vibrations mode at 241 and 282 cm^-1 in 3,4,5-trimethoxy toluene and at 282 cm^-1 in 2,3-dimethoxy toluene. Thereforein the present molecule, the Raman band at 300 cm^-1 has been identified as (C-OC2H5) out-of-plane bending vibration mode.

3.2 GROUP VIBRATIONS 3.2.1 -NO2 group

This group observed strongly at 1530-1500 cm–1 called asymmetric nitro group some what more weakly at 1370-1330 cm–1 called symmetric nitro group [23,24]. In addition, nitro compounds usually have strong aromatic ringabsorption at 760-705 cm–1. The usual o-m-p bands at 900-700 cm–1 are upset in nitro aromatics and not reliable, probably due to interaction with the out-of-plane NO2 bending frequency. Some workers [23] have assigned asymmetric nitro group at 1535 cm–1 and symmetric nitro group at 1360 cm–1 in IR spectrum of trisubstituted pyridine. In view of this assignment, the IR band 1527 cm–1 with the counterpart Raman band at 1531cm–1 has been assigned as asymmetric nitro group while the IR band assigned to symmetric nitro group respectively. This also find support from the literature [17,18].

Gupta et al [25] have assigned rocking, wagging and scissoring modes of nitro group at 550, 720 and 870 cm^-1 respectively in case of 2, 6-di-iodo-4-nitro phenol. In view of this assignment, the Raman band observed at 554 cm–1 has been assigned as NO2rocking mode, The IR band at 743 cm–1 (KBr) with counterpart Raman band at 739 cm–1 has been assigned to NO2 wagging mode while IR band at 848 cm–1 (KBr) in correlation with Raman band at 850 cm^-1 has been assigned to NO2 scissoring mode. These assignments also find support from the literature [17,18].

Since the nitro compounds shows strong absorption band between 760-705 cm–1, hence the IR band 715 cm–1 withcounterpart Raman band at 702 cm–1 shows the NO2 bending mode. Also the above assignments are in very good agreement with the corresponding assignmentsin the literature value[17,18].

3.2.2 -OC2H5 group:

The compound 2,6,3-CENP has only on ethoxy group at position 6, therefore there will be only one O-C2H5 stretching mode. Goel et al [24] and Gupta et al [25] identified this mode at 1027 cm–1 in 3-and 4-ethoxy benzonitriles and at 1020, 1025 and 1070 cm–1in 3- hydroxy-4-ethoxy, 4-hydroxy -3-ethoxy and 2-hydroxy -3-ethoxy benzaldehyde respectively.

In the present investigation, the IR band observed at 1057 cm–1 (KBr) with counterpart Raman band at 1064 cm–1 has been identified to this mode in the molecule 2,6,3-CENP.

Each C2H5 or OC2H5 group give rise to three C-H valance oscillation (2800-3000 cm–1) and three (C-H) deformation as suggested by Bellamy [17].

Some workers [19] have assigned (C-H) asymmetric stretching mode at 2998 and 2952 cm–1 2, 4-dimethoxy pyrimidine. In view of these assignments the IR band at 2968 cm–1 (KBr) with counterpart Raman band at 2979 cm–1 and 2992 cm–1 (KBr) with Raman

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band at 2996 cm–1 have been assigned toC-H) asymmetric vibration modes. The (C-H) symmetric vibration mode hasbeen assigned at IR band 2896 cm–1 (KBr) in correlation of Raman band at 2893 cm–1 in the present molecule. This also find support from the literatureat 2998 and 2952 cm–1 2, 4-dimethoxy pyrimidine. In view of these assignments the IR band at 2968 cm–1 (KBr) with counterpart Raman band at 2972 cm–1 and 2985 cm–

1 (KBr) with Raman band at 2989 cm–1 have been assigned to (C-H) asymmetric vibration modes. The (C-H) symmetric vibration mode hasbeen assigned at IR band 2889 cm–1 (KBr) in correlation of Raman bandat 2886 cm–1 in the present molecule. This also find support from the literature [23-25].

Some workers assigned [17,26,27], the two C-H asymmetric deformation due to-OO- C2H5group appear in the range 1400-1480 cm–1 while the symmetric deformation lies in the region 1350-1370 cm–1. Goel et al [24] has identified (C-H) asymmetric deformation mode at 1462, 1440 and 1423 cm–1 in 2, 3-dimethoxy toluene while the symmetric deformation at 1375 cm–1 in the same molecule. In accordance with these assignment the IR band at 1430 and 1487 cm–1 with the counterpart Raman band at 1431 and 1490 cm–1 respectively have been assigned to (C-H) asymmetric deformation mode, whereas theRaman band at 1363 cm–1 has been assigned to (C-H) symmetric mode of vibration.

This also find support from the literature value [18, 26,27]. Since the molecule has one ethoxy group, so due to ethoxy group, two C2H5 rocking modes are expected in the present molecule. These modes have been identified at IR band 1019cm–1KBr) with Raman band at 1005 cm–1 and at 1033 cm–1 in Raman spectrum. It is also in correlation with some otherworkers [25,26].

Bellamy [17] have assigned C2H5 torsion at cm^-1 in Raman spectra in benzaldehyde while Oven et al [16] assigned this mode in the region 97-112 cm^-1 for various monohalogenoanisoles. Therefore, in correlation with these assignment the Raman band observed at 100 cm^-1 has been identified for this mode of vibration.

TABLE 1 ASSIGNMENT OF VIBRATIONAL FREQUENCIES IN (cm^-1) OF 2,6,3-CENP

RAMAN IR ASSIGNMENT

107 S — LatticeVibration, C2H5 Torsion 178 VW — NO2 Torsion

192 VW — Γ (C-Cl )

220 W — C2H5Torsion 307 W — γ ( C2H5)

333 W — β (C-Cl)

380 W — γ (C-O-C)

456 MS 464 W γ Ring

470 W — γ Ring

527 MS 531 W γ ( C2H5)

554 W — NO2 Rocking

582 W — β Ring

614 W — β Ring

658 W 651 W β Ring

676 S 683 MS Trigonal Bending 702 MS 715 MS NO2 Bending 739 VW 743 MS C2 Wagging

756 VW — Ring Breathing

788 MS 783 MS Trional Bending 850 S 848 S NO2 Scissoring

871 VW — γ( C–H )

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6 921 S 917 MS γ( C–H )

1005 VW 1019 S γ C2H5 Rocking 1033 W — γC2H5 Rocking 1064 MS 1057 S v (C2H5 ) 1098 VW — v ( C–Cl )

1158 S — β ( C–H )

1182 S 1189 W β (C–H ) 1200 MS 1205 W — 1249 S — v ( C2H5 ) 1267 W — v ( C–NO2 ) 1307 S 1303 S v Ring

1315 BS — —

1332 S 1335 S v Ring

1340 BS — —

1359 W 1369 S v sym NO2

1363 BS — (C–H) asym. def.

1407 VW — v ( C–N )

1431 S 1430 MS (C–H ) asym.def.

1490 VW 1487 S (C–H ) asym.def.

1531 W 1527 S v asym NO2

1591 S 1576 S v Ring 1606 S 1605 S v Ring 2893 VW 2896 W v sym (C2H5 ) 2979 W 2968 W v asym (C2H5) 2996 VW 2992 W v sym (C2H5 ) 3060 W 3057 W v ( C–H )

3103 MS — v ( C–H )

Where:  - stretching , S– strong,vw- Very weak γ- out-of-plane bending

- in-plane bending, BS - Broad strong α- out-of-plane bending, W - Weak

sym.– Symmetric asym.- Asymmetric Def.- Deformation

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