Vibrational Spectra and Normal coordinate Calculations of 5, 6 Diamino 1H Pyrimidine 2, 4 Dione

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1 Forfaiting as a source of Finance for Global Trade Vibrational Spectra and Normal coordinate Calculations of 5, 6 Diamino 1 Pyrimidine 2, 4 Dione R.Gayathri Assistant Professor, Department of Physics, Cauvery College for Women, Tiruchirappalli Abstract This work deals with the vibrational spectroscopy of 5, 6 Diamino 1 Pyrimidine 2, 4 Dione by means of quantum chemical calculations. The fundamental vibrational frequencies and intensities of the vibrational bands were evaluated using density functional theory (DFT) using standard B3LYP method and G** basis set combinations. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. Keywords: 5, 6 Diamino 1 Pyrimidine 2, 4 Dione, DFT, FTIR, FT-Raman, Vibrational analysis. 1. INTRODUCTION Recent spectroscopy studies of Pyrimidine and its derivatives have been motivated by their biological and pharmaceutical importance. Pyrimidine and its derivatives belong to the heterocyclic group. The N- heterocyclic molecule such as pyrimidine, cytosine, uracil and their derivatives are of immense importance, because some of them are the basic constituents of DNA and RNA and play an important role in constitution properties of nucleic acids [1-3]. The normal coordinate analysis and total energy distribution calculations have been performed to understand the bonding properties and the rearrangement of electrons due to substitution of amino groups [4]. Therefore the present investigation has been undertaken to study the vibrational spectra of 5, 6 Diamino 1 Pyrimidine 2, 4 Dione molecule completely based on DFT studies. For a proper understanding of IR and Raman spectra, reliable assignments of all vibrational bands are essential. Computational methods based on Density Functional Theory are becoming widely used to predict relatively accurate molecular structure and vibrational spectra with moderate computational effort. The aim of this work is to check the performance of B3LYP Density Functional force field for the simulation of the IR and Raman spectra 5, 6 Diamino 1 Pyrimidine 2, 4 Dione with the use of the standard B3LYP method and G** basis set DFT calculations were carried out to obtain the optimized geomentries, Vibrational frequencies, IR intensities and Raman activities. 2. EXPERIMENTAL The sample 5, 6 Diamino 1 Pyrimidine 2, 4 Dione was purchased from the sigma Aldrich chemical company (USA) with a stated purity of greater than 98% and it was used as such without further purification. It is in solid form at room temperature. The FT- Raman spectrum of the title compound has been recorded using 1064nm line of Nd: YAG laser as excitation wavelength in the region cm -1 on a Brucker model IFS 66V spectrophotometer equipped with Cauvery Research Journal, Volume 3, Issue 1 & 2, Jul Jan

2 S. Yasodhai FRA 106 FT-Raman module accessory. The FTIR spectrum of this compound was recorded in the region cm -1 on IFS 66V spectrophotometer using KBr pellet technique. 3. COMPUTATIONAL DETAILS The calculation of the vibrational frequencies is essential and also useful for the vibrational assignments of the spectra. All the calculations were performed using Gaussian98w program package and the vibrational modes were assigned by means of visual inspection using GAUSSVIEW Program and also from the results of normal co-ordinate calculations [5]. The Cartesian representation of the theoretical force constants have been computed at optimized geometry by assuming c s point group symmetry. The normal coordinate analysis for the title compound has been performed on the basis of General valence Force Field (GVFF) by applying Wilson s FG matrix mechanism [6-8]. The initial set of force constants required to solve the secular equation were taken from the molecules of similar environment and those were subsequently refined by a least square fit technique using the software developed by Schachtschneidera with suitable modifications. To check whether the chosen set of assignments contributes maximum to the potential energy associated with normal coordinate of the molecules, the total energy distribution has been calculated using the final set of force constants. 4. RESULT AND DISCUSSION 4.1 Structural Properties The atom numbering system adopted for 5, 6 Diamino 1 Pyrimidine 2, 4 Dione in this investigation as shown in fig 1.The optimized values obtained for bond length and bond angles are reported in Table 1 [9].The global minimum energy obtained by DFT structure optimization is found to be artrees.the geometrical optimization study of the title compound reveals that the molecule belongs to c s point group.all the fundamental modes of vibrations were found to be IR and Raman active suggesting that the molecule possesses a non-centro symmetric structure. Table 1. Optimized and experimental geometrical Parameters of 5, 6 Diamino 1 Pyrimidine 2, 4 Dione obtained by B3LYP/6-311+G** density functional calculations Parameters Bond value Bond Angle Dihedral Parameters (Ǻ) (A O Parameters ) (A O ) N1-C N1-C2 -N C4-C5-N C2-N C2-N3 -C C4-C5-N N3-C N3-C4 -C N1-C6-N C4 -C C4 -C5 -C N1-C6-N C5-C C5-C6 -N N1-C2-C5-O8 0 C6-N C6-N N1-7-C2-N4 0 N N1- C N1-C2-N3-O9-180 C C2-N C2-N3-G4-O N N3-C4-O N3-C4-C5-N Cauvery Research Journal, Volume 3, Issue 1 & 2, Jul Jan

3 Forfaiting as a source of Finance for Global Trade C4-O C4-C5-N C4-C5-C6-N C5-N C5-N C5-C6-N1-O7 180 N C5-N N C5-C6-N C6-N C6-N N C2-N N C6-N Vibrational frequencies and normal coordinate analysis The optimized structural parameters were used to compute the vibrational frequencies of 5, 6 Diamino 1 Pyrimidine 2, 4 Dione at the DFT, B3LYP/6-311+G** level of calculations.the 42 normal modes of the title compound is distributed amongst the symmetry species as Γ3N-6 = 29a (inplane) +13 a (out-of-plane) in agreement with c s symmetry.all the vibrations were active both in Raman scattering and infrared absorption or either one according to mutual exclusion principle. The a vibrations are totally symmetric and gives rise to polarized Raman lines where as a vibrations are anti symmetric and gives rise to depolarized Raman lines. Normal co-ordinate analyzes were carried for the title compound to provide complete assignments of fundamental frequencies. For this purpose, the full set of 42 standard internal co-ordinates of 5, 6 Diamino 1 Pyrimidine 2, 4 Dione was given in table 2 and 3. A complete assignment of the fundamental was proposed based on the frequency values, infrared and Raman intensities are also calculated. Table 2 Definition of internal coordinates of 5, 6 Diamino 1 Pyrimidine 2, 4 Dione No Symbol Type Definition Stretching Pi ri Ri Qi C-N C-C C-O N- C2-N1,C2-N3,C4-N3,C5-N11,C6-N14,C6-N1 C4-C5,C5-C6 C2-O8,C4-O10 N1-7,N3-9,N11-12,N11-13,N14-15,N14-16 Bending Ti βi αi σi δi Vi Ki υi Ring C-N- N- C-C-N N-C-O N-C-N C-C-O -N- N1-C2-N3,C2-N3-C4,N3-C4-C5,C4-C5-C6,C5-C6- N1,C6-N1-C2 C2-N3-9,C4-N3-9.C6-N1-7,C2-N1-7 C5-N11-12,C5-N11-13,C6-N14-15,C6-N14-16 C4-C5-N11,C6-C5-N11,C5-C6-N14 N1-C2-O8,N3-C2-O8,N3-C4-O10 N1-C6-N14 C4-C5-O10 12-N11-13,15-N14-16 Cauvery Research Journal, Volume 3, Issue 1 & 2, Jul Jan

4 Out-of-plane Torsion Πi Ψi ωi ti ti N- C-O C-N τring τn2 S. Yasodhai 7-N1-C2-C6,9-N3-C2-C4 O10-C4-N3-C5,O8-C2-N3-N1 N11-C5-C4-O6,N14-C6-C5-N1 N1-C2-N3-C4,C2-N3-C4-C5,N3-C4-C5-C6,C4-C5- C6-N1,C5-C6-N1-C2,C6-N1-C2-N3 C5-N ,C6-N Table 3. Definitions of local symmetry coordinates of 5, 6 Diamino 1 Pyrimidine 2, 4 Dione No Symbol Definition CN CC CO N Rtrig Rsym Rassy bcn rock bn twist b CCN b NCO b NCN b CCO b N sciss ω N ω CO ω CN t Rtrig t Rsym τ Rasy N 2 wag P1,P2,P3,P4,P5,P6 r7,r8 R9,R10 Q11,Q12,Q13,Q14,Q15,Q16 T17-T18+T19-T20+T21-T22/ 6 -T17-T18+2T19-T20-T21-2T22/ 12 T17-T18+ T20-T21/2 Β23-β24/ 2,β25-β26/ 2 α27-α28/ 2,α29-α30/ 2 σ31,σ32,σ33 δ34,δ35,δ36 V37 K38 υ 39-υ40/ 2 π41,π42 Ψ43,Ψ44 ω 45,ω46 τ47-τ48+τ49-τ50+τ51-τ52/ 6 τ47-τ49+τ50-τ52/2 -τ47+2τ48-τ49-τ50+2τ51-τ52/ 12 τ 53-τ54/ Vibrational Spectra In the present study, the vibrational spectra of the title compound have been interpreted on the basis of B3LYP/6-311+G** methods and basis set combinations. A normal mode analysis was performed for the title compound according to total energy distribution. The observed FTIR and FT-Raman bands along with their intensities and their proposed assignments are presented in Table 4.The observed FTIR & FT-Raman spectra of the compound are shown in fig 2, 3 respectively Cauvery Research Journal, Volume 3, Issue 1 & 2, Jul Jan

5 Forfaiting as a source of Finance for Global Trade Table 4. Detailed assignments of fundamental vibrations of 5, 6 Diamino 1 Pyrimidine 2, 4 Dione by normal mode analysis based on SQM force field calculations Observed frequencies in Assignment Species cm -1 FTIR Raman Calculated frequencies using B3LYP/ G** in cm -1 IR Intensities Raman activity A N 2 ass A N 2 ass A N 2 ss A N 2 ss A N A N A CO,CN A N 2 sciss A CO,CN A N 2 sciss A CN A CN A CC,bN A CC,Rtrigd A CN.bCN A CN,Rasyd A CN,CC A CN,CC A bn, Rtrigd A bcn A bcn, Rasyd A bn A N 2 rock,b CN A N 2 rock,b CN A N,R asymd A R symd,bcn A ωn, trasy A N 2 wag, trsym A ωn,t R asy A R symd, Rtrigd A ωcn,t Rasymd A bco A trsym, ωn A N 2 wag, trtrigd A bco A ωcn, trsym A trtrigd, ωn Cauvery Research Journal, Volume 3, Issue 1 & 2, Jul Jan

6 S. Yasodhai A trasym, ωn A ωco, bcn A ωco, bcn A N 2 twist A N 2 twist O N N N N O Fig. 1. Molecular structure of 5,6-Diamino 1 pyrimidine 2,4-Dione Fig. 2. FTIR spectrum of 5,6-Diamino 1 pyrimidine 2,4-Dione Cauvery Research Journal, Volume 3, Issue 1 & 2, Jul Jan

7 Forfaiting as a source of Finance for Global Trade Fig. 3. FT-Raman spectrum of 5,6-Diamino 1 pyrimidine 2,4-Dione C-C vibrations In Pyrimidine, the distance between two carbon atoms changes the ring angles because of its substituents groups. The highest C-C stretching vibration of benzene is around 1600 cm -1 [10]. In substituted benzene, the vibrations should appear near 1600 cm -1 giving rise to a fairly strong bands IR and Raman spectra. In present investigation the IR and Raman bands observed at 1482cm -1 and 1432 cm -1 respectively. C=O vibrations The characteristic infrared absorption frequency of C=O are normally, strong in intensity and found in the region 1800 cm cm -1 [11-12].In the present investigation the IR and Raman bands observed at 1654 cm -1,1679 cm -1 and 1737 cm -1. N- Vibrations N- stretching vibrations of aromatic compounds occur in the region cm -1 accordingly [13], the bands observed at cm -1 are assigned to N- stretching modes of vibrations. C-N Vibrations The identification of the C-N stretching frequency in the side chains is a rather difficult task since there are problems in identifying these frequencies from other vibrations[14]. Referring the previous reference the band at 1468 cm -1, has been designed to C-N stretching mode. Amino group vibrations The rocking, twisting, wagging appear at 1245, 1034, 627 and 438 cm -1 respectively in FTIR spectrum. The amino group assignments made in this study are in good agreement with the literature values[15-16]. The remaining assignments are given in Table 4 and these assignments Cauvery Research Journal, Volume 3, Issue 1 & 2, Jul Jan

8 are supported by the normal coordinate calculations. Ring vibrations In the present study, the bands described at 1101 cm -1, 1091 cm -1, 803 cm -1,799 cm -1 have been designed to ring in-plane and out-of-plane bending modes, respectively[17-18]. For most of the remaining ring vibrations, the overall agreement is satisfactory small changes in frequencies observed for these modes are due to the changes in force constants/reduced mass ratio resulting mainly due to the extent of mixing between ring and substituent group. CONCLUSION The vibrational properties of 5, 6 Diamino 1 Pyrimidine 2, 4 Dione have been investigated by FTIR and FT-Raman spectroscopes and calculations were performed on the basis of DFT B3LYP method at G** basis set level. The energy of the title compound has been calculated using the above mentioned basis sets. On the basis of the comparison between calculated and observed results, assignments of fundamental vibrational modes were examined using scaling procedure and believed to be unambiguous. The simulated and observed IR and Raman spectra agree well with the better frequency fit and intensities. REFERENCES [1] Rastogi V.K.Mittal P Sharma YC & Sharma SN, Spectroscopy of biological molecules, (Eds) RE ester & RB Girling, (Royal society of Chemistry, London) P.403. [2] Bandekar J & Zundae G, Spectrochimica Acta, 39A (1983) 343. S. Yasodhai [3] Acheson R M, An introduction to Chemistry of heterocyclic compounds, Third edition, (John Wiley & sons, New York), [4] C.N.Banwell, Fundamentals of Molecular Spectroscopy, Tata McGraw ill (1972). [5] J.M.Schachtschneider, Vibrational analysis of poly atomic molecules. Vol. V and V1, FORTRN IV programmes, Technical report Shell Development company, Emery Ville, California (1964). [6] K.V.Raman, Group Theory and its Application to Chemisry, Tata McGrawill, New Delhi (1990). [7] Paul O.P.Ts O, Basic principles in nuclei acid Chemistry Vol.1 (Academic press, London), [8] Martin G T, Biological antagonism, (Blakiston, New York), 1961 [9] Sutton LE, The interatomic bond distances and bond angles in molecules and ions (Chemical society, London), [10] Schachtschneider J, Technical report (Shell development company, Emery Ville,CA, VSA), [11] Susi & Ard J S, Spectrochimica Acta, 27A (1971) [12] Bellamy C J, The infrared spectra of complex molecules, (John wiley, New york),1959. [13] Pinchas S, Samuel D & Weiss Broday M, J Chem Soc, (1961) [14] Mohan S et al., Spectrochimica Acta, 47A (1991) [15] Krishnakumar V et al., Indian J pure & Appl phy, 36 (1998) 171. [16] Mohan S, Sundara Ganesan N R Mink J, Spectrochemical Acta, Vol.474 (1991)1111. [17] Krishnakumar V & Balachandran V, Indian J pore Appl. Phys. 39 (2001) 623. [18] Chithambarathanu T, Umayorubhagan V & Krishnakumar V, Asian J Chem, 13 (2001) Cauvery Research Journal, Volume 3, Issue 1 & 2, Jul Jan