Spectral Characterization and Vibrational Assignments of Ethyl 4-( 3-( 2 , 3-Dihydrobenzofuran-5-Carboxamido ) Phenyl )-6-Methyl-2-Oxo-1 , 2 , 3 , 4-Tetrahydropyrimidine-5-Carboxylate by Ab Initio Density Functional Method

In the present investigation, then novel compound ethyl 4-(3-(2,3-dihydrobenzofuran5carboxamido)phenyl-1,2,3,4-tetrahydro-6-methyl-2-oxopyrimidine-5-carboxylate(DFOC) were synthesized .The synthesized compound have been characterized by using UV-visible, FT-IR, FT-Raman,1H-NMR and 13CNMR spectral studies. The harmonic vibrational frequencies, optimized molecular geometry have been carried out with the help of B3LYP density functional theory method. The stability of the molecule was analyzed by means natural bond orbital analysis and delocalized p-p* interactions. Moreover, the frontier molecular orbital analysis, molecular electrostatic potential surface and thermodynamic properties of DFOC were investigated using DFT calculations. keywords: DFOC, NBO, NLO HOMO-LUMO and DFT.


Computational details
The theoreticalcalculation of DFOC were performed quantum chemical calculations of DFOC have been performed usingGaussian 03 program package utilizing DFT/ 6-31G(d,p) the B3LYP level of theory 17-19.By using VEDA4 program, FT-IR, FT-Raman frequencies are on the basis of potential energy distribution. 20The calculated wave number were scaled down uniformly by a factor of 0.9608 for obtaining a decent agreement with experimental results.

Spectral measurements
The FT-IR spectrum of the synthesized DFOC was measured in the 4000-400 cm -1 region at the spectral resolution of 4 cm -1 using on SHIMADZU FT-IR affinity Spectrophotometer (kBr pellet technique).The UV spectrum has been recorded with SHIMADZU-1650 spectrophotometer (l max nm) in spectral grade methanol solvent.NMR spectral studies were carried out using Bruker 300 MHz spectrometer, using TMS as an internal standard and DMSO-d 6 as solvent and recorded at Indian Institute of Technology (IIT), Chennai.

Molecular geometry
The optimized geometrical parameters of DFOC using DFT/B3LYP6-31 G(d,p) level of theory.The optimized structure of DFOC as shown in fig( 1

Natural bond orbital Analysis
The NBO is an efficient method to analyze the charge transfer interaction of a molecular system 23 .In the present investigation the strong delocalization in the aromatic system gives rise the orbital overlap between the p(C-C)→ p*(C-C) interactions gives the strong intra molecular interactions resulting in the p-conjugation due to the p-electron delocalization.These interactions are observed as an increase in electron density (occupancy) in (C-C) antibonding orbitals that weakens the respective bonds 24 .In our study the strong intramolecular interaction between pC 1 -C 2 →p*C 14 -O 16 since the stabilization energy of 104.56 kJ/mol.In addition, the interaction between n (O 15 )→p*C 14

Vibrational Assignments
The molecular structure of DFOC belongs to C1 point group symmetry there would not be any relevant distribution.The title molecule consists of 56 atoms and expected to have 156 normal modes of vibrations (3N-6).The complete vibrational assignments along with the frequencies are presented in Table 3.The both recorded and simulated spectra of FT-IR and FT-Raman are shown in Fig (2) and Fig ( 3).

Ring 1
In aromatic heterocyclic compounds, the N-H stretching vibrations occur in region 3450-3250 cm -125 .The N-H stretching frequency observed at 3370cm -1 for aryl amide analogues 26 .
In the present study the νN 34 -H 36 stretching modes are observed at 3277cm -1 respectively in FT-IR.The lower in frequencies in solid phase may attribute due to hyper conjugation interaction arises with the adjacent carbonyl group.The strong band observed in the region 1715-1600 cm -127 .In the present work, the very strong band observed at 1701cm - 1 in FT-IR and also very strong band at 1700cm -1 in FT-Raman are assigned for the νC 35 =O 37 stretching vibration with 79% PED contribution.The scaled wave number, at 1690 cm -1 in B3LYP method.The C-H stretching vibrations of benzofuran appear in the region 3148-3063 cm-1 28.In our investigated molecule the aromatic C-H stretching vibrations observed at 3105 cm -1 in FT-IR and its corresponding theoretical wavenumber at 3104, 3092 and 3057 cm -   (2) means energy of hyper conjugative interaction (stabilization energy).
b Energy difference between donor(i) and acceptor(j) NBO orbitals.c F(i,j) is the fork matrix element between i and j NBO orbitals.

Ring
Aromatic C-H stretching vibrations are expected to observed in the region 3115-3074 cm -1 29 .In our molecule the aromatic C-H stretching vibrations observed at 3067 cm -1 in FT-Raman spectrum.The C=C stretching vibrations of phenyl rings are assigned region of 1625-1430 cm -1 .In the phenyl ring, the six carbon atoms undergo coupled vibrations called skeletal vibration 30,31 .For our present work, the ring C=C stretching vibrations are calculated in theoretical wave number at 1597,1582 cm -1 , respectively.The strong bands observed at 1592 cm "1 in FT-Raman spectrum.In our present study, the bands computed at 1101, 1088 cm-1 are assigned to trigonal bending and breathing mode of the phenyl ring and these bands shows good agreement with experimental FT-IR bands at 1093 cm-1 , and FT-Raman bands at 1086 cm -1 .

Ring 3
In the present study, N-H stretching modes are observed at 3270, 3210cm -1 for dihydropyrimidine 32 .The νN 5 -H 8 ,νN 7 -H 6 stretching modes are observed at 3369 and 3277cm -1 respectively in FT-IR.The lower in frequencies in solid

Nonlinear optical property
Nonlinear optical material has vast applications in the field of telecommunication, optical interconnections and optical memory for emerging technology in the area of signal processing 40,41 .In the present study, NLO property of the title molecule has been theoretically predicted and the results are present in the Table 4. From the results, the total dipole moment of the title molecule (2.5589 Debye) is mainly attributed to an overall imbalance in charge.The first hyperpolarizabilty are calculated about 2.936 x10 -30 esu.The b 0 value of the title compound is six times greater than that of standard urea.Urea is one of the prototypical molecules used in the study of the NLO properties of molecular systems.Hence the investigated molecule a good nonlinear optical material.

Frontier molecular orbital analysis
The frontier molecular orbital analysis (FMOs) were mainly used to predict chemical reactivity, stability and biological implications of a molecular system 42 .predicting the most reactive position in p-electron systems and also explained several types of reactions in conjugated system 43 .As can be seen from the figure 4 HOMO is located on dihydrobenzofuran and partially over pyrimidine ring.By contrast, LUMO is located over dihydropyrimidine with carboxylate side chain of DFOC molecule.Hence, electron delocalization mainly takes place in carboxamide moiety and is also evident from enormous stabilization energy of -CONH from NBO analysis.The small energy gap of ΔE = 4.5765eV is corresponding to the chemical reactivity of the molecule.The globule reactivity descriptors and ΔE values of DFOC is shown in table 5.

NMR-analysis
The NMR spectroscopy is currently used for structural analysis and functional group determination of biological macromolecules.The experimental and simulate NMR chemical shifts are presented in Table 6.The observed 1 H and 13 C NMR spectra of the title molecule are given in Fig. 6 In the 1H-NMR chemical shift of title molecule, a singlet at 10.04 ppm confirmed the presence of carboxamido moiety.Moreover, two singlets observed at 9.16 and 7.94 ppm are corresponding signals of two N 5 -H 77 and N 7 -H 9 protons of the dihydropyrimidinone ring.The multiples at 6.86 to7.85 ppm for seven aromatic protons indicate the presence of benzene and benzofuran ring, which correlates to the calculated chemical shift at 6.94-9.29 ppm respectively.In addition, the singlet peak appeared at 2.24 ppm mark the methyl hydrogen in the dihydropyrimidinone ring, and another methyl proton observed at 1.16 -1.46 ppm as triplet represents the ester group.As can be seen from Table 6, the theoretical chemical shift values are closer agreement with experimental results.

Molecular electrostatic potential
MEP is useful discriptors for determining the reactive sites and hydrogen bonding interactions of the molecule. 46,47Accordingto the calculated results the maximum positive region is localized on the N-H bonds (N 5 -H8, N 7 -H 6 , N 34 -H 35 ), indicating a possible site for nucleophilic attack.The MEP map shows in fIg. 5 that the negative potential sites are on electronegative carbonyl oxygen atoms (O 9 , O 16 and O 37 ) and the positive potential sites are around the hydrogen atoms.These sites give information about the region from where the compound can have intermolecular interactions.This predicted the most reactive site for both electrophilic and nucleophilic attack.

UV analysis
In order to understand the electronic transitions of DFOC molecule were performed by TD-DFT method.From fig. 7 the absorption maximum of investigated molecule observed at 282 nm and this band is due to the p→p* transition of themolecule.The intensity of the band is very high.The absorption maxima (284 nm) of DFOC is calculated, by TD-DFT/6-31G(d,p) level of theory.The predicted results involving the vertical excitation energies, oscillatorstrength (f) and wavelength are carried out and are listed in Table 7.

CONCLUSION
This works reports the synthesis and computational analysis of nonlinear molecule ethyl 4-(3-(2,3-dihydrobenzofuran-5-carboxamido) p h e n y l ) -1 , 2 , 3 , 4 -t e t r a h y d r o -6 -m e t h y l -2oxopyrimidine-5-carboxylate.The structure was determined and characterized by UV-visible, FT-IR, FT-Raman and NMR spectral studies.The NBO results reveals the strong hyperconjugative interactions occurs in the molecule leads to the highest stabilization energy of of the molecular system.The investigated DFOC have small energy gap 4.5765eV is responsible for the nonlinear optical activity.The first hyperpolarizabilty calculated as 2.936 x10 -30 esu, which is eight times greater than that of reference urea.The effect is even more important for nonlinear molecule with strong intramolecular charge transfer from electron donor group to electron acceptor group (D-П-A) interacting through a conjugated П system.The UV-visible absorption analysis, mainly takes place П -П * transition of the title molecule.The charge sites are identified by the molecular electrostatic potential mapped surface.

1 respectively.
In furan νC 45 -O 47 stretching modes are calculated at 1239 cm-1 higher frequency.Because the bond angle of C-O-C have more angle strain.The bond angle in furan (C 45 -O 47 -C 48 ) 107.60 and in esterC 14 -O 15 -C 17 to give115.56

Fig. 2 & 3 :
Fig. 2 & 3: The recorded and calculated FT-IR spectra of DFOC phase may attribute due to resonance delocalization of dihydropyrimidine ring.The C-N stretching absorption in the region 1382-1266 cm -1 33.The C-N stretching vibration coupled with scissoring of N-H is moderately active in the region 1275±55 cm - 134 .For the pyrimidine ring, the four νC-N stretching vibrations are identified with the help of PED analysis.The C-N stretching wavenumbers are calculated at 1335 and 1216 cm-1.In pyrimidine molecule C=C stretching observed at 1645cm-1 and 1650-1710 cm-1.In our present investigation the νC1=C2 stretching vibration occurs at 1544 cm-1 in FT-IR and 1546 cm-1 in FT-Raman spectrum.The magnitude of C=C stretching frequency is lower than the expected value is due to presence of carboxylate substituent in the neighbouring atom.The p electron conjugated with the carboxylate group.Generally the carbonyl groups are appeared in the region 1700-1660

Fig. 7 :
Fig. 7 : The experimental and simulated UV-spectra of DFOC molecule ).The geometrical geometrical parameters such as bond length, bond angle and dihedral angle are listed in table 1 and compared with available crystal data of analogous molecule 21 .The bond length of C 4 -O 9 , C 14 -O 16 , and C 35 -O 37 are calculated as 1.2219, 1.2249 and 1.2271Å respectively from the B3LYP method.All the above C=O bond lengths are more or less equal one to other because they are conjugated with a phenyl group and mesomeric effect of ethoxy group in ester moiety.The C 4 , C 14 , and C 35 atoms are having SP 2 hybridization.The bond length for C 14 -O 15 , O 15 -C 17 , C 45 -O 47 and C 48 -O 47 are calculated about 1.3582, 1.4454, 1.3604 and 1.4535 Å.In which the bond length of C 14 -O 15 is very lower value O 15 atoms having inductive effect dominate mesomeric effect 22 .

Table 2 : Second order perturbation theory analysis of NbO basis for DFOC
a E

Table 4 : The Non-Linear Optical properties of DFOC
Scheme1: The reaction scheme for synthesis of DFOC