Molecular Structure and Vibrational Analysis Of 2-(4-Methoxyphenyl)-2, 3-Dihydro-1H-Perimidine Using Density Functional Theory

The compound 2-(4-methoxyphenyl)-2, 3-dihydro-1H-perimidine (MPDP) was synthesized. The molecular structure and its functional groups were characterized with the help of Fourier Transform Infrared: FTIR/ Fourier Transform FT-Raman spectra in the regions of 400-4000/50-4000cm, respectively. The geometrical parameters, harmonic vibrational wavenumbers, Infrared (IR) & Raman scattering intensities, Nuclear Magnetic Resonance (NMR) chemical shift and Ultraviolet-Visible (UV-Vis) spectra were computed using B3LYP/6-311++G(d,p) level of theory. The complete vibrational analysis were made on the basis of Potential energy distribution (PED) calculation with the help of VEDA4 programme. The Highest occupied molecular orbital (HOMO) – Lowest unoccupied molecular orbital (LUMO) energy gap and intra-molecular charge transfer (ICT) were studied using NBO analysis. The first order hyperpolarizability (β0) and other related properties (β, α0, Δα) of MPDP were computed. The molecular electrostatic potential (MEP), Mulliken atomic charges were calculated using the same level of theory. In addition, the various thermodynamic parameters were also calculated. Corresponding author : H. Saleem, Department of Physics, Annamalai University, Annamalainagar 608 002, Tamil Nadu, India. E-mail: saleem_h2001@yahoo.com

Higher π acidity and the presence of more than one hetero atom in pyrimidine play an important role in its co -ordination chemistry, compared to that of pyridine bases, and serve as better models in biological systems [7][8][9]. Because of perimidine group of organic molecules are reported at scarce. Usually the heterocyclic compounds are used to drug designing in the organic system and the great importance due to possible promising in medical applications [10][11][12][13][14][15][16]. Such compounds undergo oxidative aromatization and hydrolysis of the dihydropyrimidine ring. Preparative methods have been developed to facilitate the selective oxidative aromatization or hydrolytic elimination of the dihydropyrimidine fragment of the compounds [17]. This kind of compound have been attractive for physicochemical applications of non-linear optical [18], electrical property [19], chelating agents in metal-ligand chemistry as fluorescent liquid crystals [20]. Dihydropyrimidinones, the product of the Biginelli reaction, are also widely used in the pharmaceutical industry as calcium channel blockers and alpha-1 antagonists [21].
Moreover, some bioactive alkaloids such as batzelladine B, containing the dihydropyrimidine unit, which has been isolated from marine sources, show anti-HIV activity [22].

FT-IR, FT-Raman, NMR and UV-Vis spectra details
The FT-IR spectrum in the spectral range 4000-

Computational methods
The entire calculations were performed at DFT levels on a Pentium IV/3.02 GHz personal computer using Gaussian 03W [25] program package, invoking gradient geometry optimization [25,26]. In this study, the density functional three parameter hybrid model DFT/B3LYP/6-311++G (d,p) basis set was used to calculated various properties of the title molecule. The vibrational modes were assigned on the basis of TED analysis with the help of VEDA4 program [27] and by combining results of Gauss View program [28] with symmetry considerations. It should be noted that the Gaussian 03W package is unable to calculate the Raman activity. The Raman activities were transformed into Raman intensities using Raint program [29] by the expression: Where I i is the Raman intensity, Ai is the Raman scattering activities, m i is the wavenumber of the normal modes and m 0 denotes the wavenumber of the excitation laser [30].

Molecular docking study:
Molecular docking experiment was carried out to study the exact binding location of ligand on protein.    and C3-C8-N18-C21 is -29.26. This dihedral angle indicated that N17-C21-N18 ring portion projected in the upward direction to attain the twisted boat configuration. This twisted boat configuration is attained due to the steric effect of methoxy group substituted at C 21 atom.

C-H vibrations:
The bands vibrating at 2935, 2851cm -1 in FTIR spectrum were ascribed to C-H stretching vibrations of perimidine ring in TDP by M. Alum et al., [23]. The scaled harmonic frequencies in the range 3059-3032cm -1 (mode nos:6-9, 11, 12) are attributed to ν C-H modes of perimidine ring MPDP. It should be mentioned here that these ν C-H modes are pure and having >98% of PED value.
Literature survey [37,40] revealed that the C-O-CH 3 angle bending mode have been assigned in the region of 300-670cm -1 for anisole and its derivatives.

C-N Vibrations:
Generally the ν C=N /ν C-N vibrations were observed in the regions of 1600-1670 cm -1 /1266-1382cm -1 [34,41]. According to the work by Z.Li and W. Deng These assignments are having >26% of PED and also find support from literature [36].

C-C Vibrations:
Freely According to PED results the β CCC and Γ CCC vibrations are mixed with β CH mode.

Nonlinear optical effects (NLO)
The NLO materials have recently attracted much interest because they involve new scientific phenomena and also they offer potential applications in emerging optoelectronic technologies, telecommunications, information storage, optical switching and signal processing [45]. The output from GAUSSIAN 03W provides 10 components of the 3x3x3 matrix as βxxx; βxxy; βxyy; βyyy; βxxz; βxyz; βyyz; βxzz; βyzz; βzzz; respectively. The total static dipole moment (µ), polarizability (α 0 ), and the first hyperpolarizability (β 0 ) can be calculated by using the following equations, The dipole moment, polarizability and the first hyperpolarizability were calculated using B3LYP/6-311++G(d,p) basis set. As can be seen from Table 4 esu, respectively. The first order hyper polarizability (β 0 ) value is 18 times greater than that of urea and hence the molecule has good NLO property.

NBO analysis:
The non-covalent bonding and anti-bonding interaction can be quantitatively described in terms of the NBO analysis, which is expressed by means of the second-order perturbation interaction energy (E (2) Table 5. The intramolecular hyperconjugative interactions energes are formed by the orbital overlap between π(C-C) and π*(C-C) bond orbitals, which results intra molecular charge transfer (ICT) causing stabilization of the system.

Homo-Lumo analysis
The frontier molecular orbitals play an important role in the optical and electric properties, as well as in quantum chemistry. The frontier molecular orbital gap also helps to characterize the chemical reactivity and the kinetic stability of the molecule. A molecule with a small frontier orbital gap is generally associated with high chemical reactivity and low kinetic stability and is also termed as soft molecule [51].  Table 6. The density of state (DOS) of the present molecule has been plotted and shown in Fig.6. DOS denoted the number of available molecular orbitals at different energy.

Mulliken charges
The

MEP analysis
In the present study, 3D plots of molecular electrostatic potential (MEP) has been drawn in Fig. 9.
The MEP is a plot of electrostatic potential mapped onto the constant ED surface. The different values of the electrostatic potential at the surface are represented by different colors. Potential increases in the order red < orange < yellow < green < blue. The color code of the MEP map is in the range between -9.517e-2 (deepest red) and 9.517e-2 (deepest blue) and the, blue colour represents the strongest attraction and red represents the strongest repulsion. The MEP map shows, the Chemical Potential (µ) 3.043 Electronegativity (χ) -3.043eV Hardness (η) -3.043

Thermodynamic properties
The thermodynamic functions such as entropy (S), heat capacity at constant pressure (Cp) total and enthalpy (E) for different range (100-1000 K) of temperatures are determined and these results are presented in the Table. 9. The thermodynamic functions are increasing with temperature ranging from 100 to 1000 K due to the fact that the molecular vibrational intensities increase with temperature [53]. The correlation graph between thermodynamic functions and its different temperatures are graphically represented in