International Journal of Engineering & Science ...

IJESR/November 2013/ Vol-3/Issue-11/644-647

e-ISSN 2277-2685, p-ISSN 2320-9763

International Journal of Engineering & Science Research

ELECTRONIC SPECTRA AND SOLVENT EFFECT OF SUBSTITUTED NITRO PYRIDINE Gagan Deep*1 , Vipin Kumar2, Sushil Kumar3 1

Research Scholar, Dept. of Physics, Mewar University, Chittorgarh, Rajasthan, India. 2

Dept. of Applied Sciences, Ideal Inst. of Tech, Ghaziabad (U.P), India. 3

Dept. of Physics, SRM University, Ghaziabad (U.P), India.

ABSTRACT The N-heterocyclic molecules like pyridine, pyrimidine, cytosine, uracil etc. and their derivatives are of the considerable antifungal, biological and pharmaceutical importance. Pyridine molecules and their derivatives are the constituents of DNA and RNA and hence plays a vital role in the formation and properties of the nucleic acids. The electronic spectra of 2-chloro-6-ethoxy-3-nitro pyridine have been recorded and analyzed in different solvents. The effect of solvents transitions have also been explained and discussed

1. INTRODUCTION The N-heterocyclic molecules that have been explored for developing pharmaceutically important molecules, pyridine has shown an important role in the medicinal chemistry. Pyridine molecules and their derivatives are the constituents of DNA and RNA and plays a central role in the structure and properties of nucleic acids. Literature survey indicates that pyridine derivatives have attracted significant attention as they are endowed with wide spec rum of activities like antifungal [1,2] , antibacterial [3,4] , herbicidal [5], and antimicrobial [6] etc. In contrast to this, several workers have reported effective antifungal activity in various pyridines. Also pyridine derivatives like amino pyridines and marcapto pyridine etc. are widely used as drugs in certain diseases [7]. Jesson et al [8] have shown that the pyridine molecule has planar structure in the ground state and a quasi planner one in the excited state. Also, the alkaloids 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 numerous diseases and in animal metabolism. Pyridine and its derivatives are widely used as a solvent and as a synthetic intermediate in analytical chemistry. So, the knowledge of the molecular structure, physio-chemical properties and vibrational studies of pyridine and its derivatives are helpful for better understanding of their functions in several biological processes and analysis of the complex systems. The absorption spectra of pyridine and substituted pyridines have been predicated theoretically and practically by Medhi et al [9-13] have found the evidence of the presence of electronic transitions as n-π* π-π* and π-σ*. Thus the detailed study of the electronic transitions of substituted pyridines is of importance in order to check the presence of n-π* π-π* and π-σ* transitions [14]. In view of the above discussion, the present chapter reports the ultraviolet spectra in different solvents of the 2-chloro-6ethoxy-3-nitro pyridine is reported and discussed.

2. EXPERRIMENTAL Spec-pure grade sample of 2-chloro-6-ethoxy-3-nitro pyridine (abbreviated as 2,6,3-CENP) was obtained from M/S Aldrich Chemise, West Germany. The purity of sample was confirmed by elemental analysis and melting point determination. The ultraviolet 1900-4000 Å. on Beckman model M-35 Spectrophotometer in different polar solvents. All solvents used were of spectroscopic grade. The concentration of the solutions in all the cases was kept constant 8×10–3 gm/liter.

*Corresponding Author

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3. RESULTS AND DISCUSION The molecular structure of 2-chloro-6-ethoxy-3-nitro pyridine is given in Figure 1. The ultraviolet absorption spectra of the said molecule in different solvents are shown in Figure 2. The various bands observed in electronic spectra are given in Table 1

NO2 N

Cl

OC2H5

Fig 1: Molecular Structure of 2,6,3-CENP

4. ELECTRONIC SPECTRA Some workers [15] have suggested, in pyridine the introduction of -N = group in place of -CH in benzene, exhibits a red shift in π-π* and n-σ* transitions and blue shift in n-π* transitions. In the present study, the UV spectra of the molecule 2,6,3 CENP was recorded in different solvents viz. methanol, ethanol, and water but the band system which corresponds to 1A→1U transitions n-π* has been observed between 2950-3100 Å [16, 17]. The band system which corresponds to 1

1 A1g→ B2u transitions (π-π*) has been observed between 2300-2500 Å for the molecule 2,3-dihydroxy pyridine while

1 1 the band system which corresponds to A1g→ B1u transitions (n-σ*) has been observed between 2000-2100 Å for the molecule 2,3-dihydroxy pyridine. In view of this, the n-π* transitions around 3000 Å in 2,6,3 CENP is taken to represent out-of-plane transition, while π-π* and n-σ* transitions around 2770, 2250 Å in-plane transitions originated from A1g→B1u transitions respectively. In which the later one derives from A →B transitions [18]. 1 1

5. SOLVENT EFFECT The electronic spectra of a molecule when recorded in a solvent generally shifts the band in comparison to those obtained in the vapour phase. This is called the solvent shif effect and is due to the weak physical interaction between solute and solvent atoms. The interactions may be generally classified into specific solvents effect include ionisation charge transfer, aggregation phenomenon and hydrogen bonding of molecules. Non specific is due to the dispersive induction electrostatic forces that may occur between solute and the surrounding solvents molecules. Solvent polarity effect the electronic transition and this depends on whether the solute becomes more or less polar after excitation polar solvent (polar solvents are those solvents which can form hydrogen bonding [19] tend to interact electro-statistically with various chromospheres. This changes the charge distributions in the molecule and results in increases delocalisation [20] for for π-π* transitions, both the ground and excited states are stabilized and the absorption moves towards longer wavelength. For n-π* transition, the ground state is more stabilized than the excited state and consequently absorption to the shorter wavelength. Dyer [21] has also reported a red shift for π-π* transitions and a blue shift for n-π* transitions with the increasing polarity of the solvents. During the present investigation, the n-π* transitions around 3000 Å is blue shifted in 2,6,3 CENP with increasing polarity of the solvents (ethanol→methanol→water) which is identical to the trend reported for these transition in the literature value [15]. This shift is due to momentary polarization of the solvents by the transitions dipole of the solute. The polarity of the solute also plays an important role in the electronic transitions. In the present study, the molecule 2,6,3, CENP is non-polar, the shift of absorption spectra of slightly polar solute are predominantly due to the dipoledipole interactions between the solute and solvent in the ground and excited state respectively and the orientation in the excited state. The orientation will result in a blue shift if the solute dipole increases and a red shift if the solute decreases

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on excitation. These shifts are related to vapour phase spectrum [17]. With a polar solute in a non-polar solvent, dipole induces dipole interaction takes place and there will no orientation strain. Therefore, a blue shift may appear while going from vapour state to non polar solvent.

Fig 2: Ultravoilet Absorption Spectra Of 2,6, 3-CENP In (1) Ethanol (2) Methanol, (3) Water As the solute is non polar therefore no orientation strain will occur and there may be slight packing strain due to the interaction among themselves to from a cage around the solute molecule resulting a blue shift. The 3000-3200 Å system of the compound clearly shows a blue shift in n-π* transitions. It was observed by some workers [20,22] that short wavelength 2100 Å is highly solvent dependent and is affected by hydrogen bonding. Hydrogen bonding will lower the energy of ground state more than that of excited state which consequently increase the excitation energy in a blue shift. Copyright © 2013 Published by IJESR. All rights reserved

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High dielectric constant leads to a higher transition energy and an emergence of a short wavelength band would be expected. During the present study in the said molecule, the shortest wavelength system 2250 Å has been observed in 2,6,3-CENP. Further more, the greater the polarity of the solvent, the greater the attraction between solute and solvent molecules. Thus, the system would be more stable [23]. Also with increasing dielectric constant of the solvent the ionizing potentiality of the solute molecule is increased. The higher the polarity of the solvent, the greater will be the degree of salvation [23,24]. Table 1: Analysis of Electronic Spectra of 2,6,3-CENP (All values are in Å) SOLVENT

DC*

RI**

n-π π*I

Ethanol 24.3 1.3773 Methanol 30.0 1.3362 Water 80.0 1.3380 *DC= Dielectric Constant **R.I.= Refractive Index

n-π π*II 3000 3000 3180

π-π π* I 2770

π-π π* II -

n-σ σ* 2250 2260 –

REFERENCES [1] Singh T, Sharma S, Srivastava VK, Kumar A. Arch. Pharm. Chem. Life Sci 2006; 2239: 24-31. [2] Popat KH, Kachhadia VV, Nimavant KS, Joshi HS. J. Indian. Chem. Soc. 2004; 157-159. [3] Hoetin, Hans (Squibb, ER., and Sons Inc., Fr. Demande 2, 430, 946, 08 FE 1980, US appl. 923, 418, 10 jul 1978 Chem Abstr. 1980; 93: 980. [4] Singh T, Srivasta VK, Sexana KK, Kumar SL, Kumar A. Arch. Pharm. Chem. Life Sci 2006; 339: 446-672. [5] Khaus W, Heim WD, Andre T. chem.. Abster 1994; 121: 1105. [6] Bhatt AH, Parkh HH, Parikh KA, Parikh AR. Indian J chem. Soc 2001; 40: 21-27. [7] Mohan S, Illangovan. Proc. Nat. Acad. Sci., India. 1995; 65(A). [8] Jesson JP, Kroto HW, Ramsay DA. J. Chem. Phys., (USA), 1972; 56: 6257. [9] Medhi KC. Indian J. Pure & Appl. Phys. 1977; 51(A): 399. [10] Medhi KC. Indian J. Pure & Appl. Phys 1981; 55(B): 479. [11] Medhi KC. Bull. Chem. Soc. japan 1983; 56: 3456. [12] Medhi KC. Spectrochim. Acta 1987; 42(A): 1231. [13] Medhi KC. Indian J. Phys. 1982; 38(A): 717. [14] Green JHS, Harrison DJ. Spectrochim. Acta 1973; 32(A): 1279. [15] Ram K, Pandey BR, Tripathi RS. J. Chem., Phys. 1977; 74: 1150. [16] Murrell JN. The theory of the electronic spectra of organic molecules, Chapman and Hall, London, 1971. [17] Suzukim H Electronic Absorption Spectra and Geometry of Organic Molecules, Academic Press, New York, 1967. [18] Hug W, Tinocco E. J. Amer 1973; 95: 2803. [19] Okofar EC. Spectrochim. Acta 1980; 36(A): 207. [20] Shashidhar MA, Ayachit NH, Shanbhag PV, Suryanarayana Rao K. Indian J. Pure & Appl. Phys. 1984; 22: 489. [21] Dyer JR. Application of Absorption Spectroscopy of Organic Compounds, Printice Hall Inc., Englewood Chiffs, USA, 1965. [22] Takahashi M, Kumura K.. J. Chem. Phys. 1992; 97: 2920. [23] Finar IL. Organic Chemistry, English language Book Soc., U.K, 1973. [24] Yadav BS. Acta Ciencia indica 1991; 2: 133.

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