Structural and Vibrational studies on (E)-1-(4- methoxybenzylidene) Semicarbazide (MBSC) using experimental and DFT methods

FT-IR, FT-Raman spectra were recorded for the MBSC compound in the solid state. The equilibrium geometries, harmonic vibrational frequencies, FT-IR and FT-Raman scattering intensities were computed using the Gaussian 03 package. Computations were made using density functional theory (DFT) with B3LYP/6-311++G (d, p) basis set level. The optimized geometrical parameters obtained from DFT calculations are in good agreement with the reported single crystal XRD data of the same molecule. Results obtained were used for a detailed interpretation of the Infrared, Raman based on the total energy distribution (TED) of the normal modes. Introduction The benzylidene derivatives are intermediates in various pharmaceuticals, agro chemicals and perfumes. Semicarbazones known to have antiviral, antibacterial and antifungal effects in the field of medicine, pest control and used as drugs to cure diseases. Experimental details Synthesis The 2.1 mL (0.025mol) ethanolic solution of anisaldehyde was added to (0.025mol) 2.8 g of Semicarbazide hydrochloride . The reaction mixture was taken in a round bottom flask and kept over a magnetic stirrer and stirred well in ice cold condition for two hours. The white precipitate obtained was filtered and dried over vacuum. The product was recrystallized from absolute alcohol. Spectroscopic studies The FT-IR spectrum of MBSC was recorded in the region 4004000cm-1 on Shimadzu spectrometer using a KBr pellet technique, which was carried out from the Instrumentation laboratory, Jamal Mohamed College, Tiruchirapalli, Tamilnadu. The FT-Raman spectrum of MBSC has been recorded using 1064nm line of Nd: YAG laser as excitation wavelength in the region 50-4000 cm-1 on Bruker RFS27 model spectrometer at the spectral resolution of 2cm-1 carried out from SAIF laboratory, IIT(M), Tamilnadu, India. The ultraviolet absorption spectrum of MBSC is examined in the range of 200-500nm using Perkin Elmer Lambda 35 spectrometer. The UV pattern is taken from a 10-5 molar solution of MBSC dissolved in methanol and the report was taken from ACIC, St.Joseph’s College, Tiruchirapalli, Tamilnadu. Molecular geomentry The molecular geometry of (E)-(1)-(4-methonybenzylidene) semicarbazide (MBSC) was studied by the B3LYP/6-311++G (d, p) level of calculation. The geometrical parameters such as bond length, bond angles and dihedral angle are plays a vital role in the formation of molecular structure and its properties. In order to understand the molecular geometry of MBSC, the title molecule was compared with the literature [1]. The bond length of C1-C2, C2-C3, C3-C4, C4-C5, C5-C6, and C1-C6 are calculated as 1.406, 1.401, 1.390, 1.401, 1.400 and 1.385Å respectively and the respective corresponding recorded values (XRD) are about 1.395, 1.396, 1.383, 1.382, 1.392 and 1.372 Å [1]. The bond length of ring carboncarbon C-C bond coincides well with literature values. The bond length of methoxy group oxygen with carbon ring lies about 1.361 Å and the recorded value appeared at 1.372 Å [a]. Similarly the bond length between oxygen and methyl group lies about 1.423AO and the XRD value appeared at 1.437 Å. The bond–length recorded for C=N and C-N were about 1.280 and 1.371 Å, its calculated bond length were lies in the ranges of 1.283 and 1.392AO respectively. The bond N-N being as fuse between C=N and C-N was calculated and recorded about 1.392 and 1.371 Å, which is coincided well with each other. Due to the electron density in C-NH3 and C=O the bond length of the same decreases when compare with σ bond group. In evident with this the C21=O22 and C21N23 bond length lies about 1.220 and 1.364 Å which were recorded about 1.241 and 1.336 Å respectively. The bond angle of methoxy group with the benzene ring (CO-C) is calculated as 118.87o and the recorded value of the same was about 117.38 o, it shows a good consent with gas phase molecule. Similarly the calculated and recorded bond angles of N19-C21O22 and O22C21N23 are shown very good agreement with each other. The optimized molecular structure of MBSC is shown in fig. 1 and the calculated bond parameters are presented in Table.


Introduction
The benzylidene derivatives are intermediates in various pharmaceuticals, agro chemicals and perfumes. Semicarbazones known to have antiviral, antibacterial and antifungal effects in the field of medicine, pest control and used as drugs to cure diseases.

Experimental details Synthesis
The 2.1 mL (0.025mol) ethanolic solution of anisaldehyde was added to (0.025mol) 2.8 g of Semicarbazide hydrochloride . The reaction mixture was taken in a round bottom flask and kept over a magnetic stirrer and stirred well in ice cold condition for two hours. The white precipitate obtained was filtered and dried over vacuum. The product was recrystallized from absolute alcohol.

Spectroscopic studies
The FT-IR spectrum of MBSC was recorded in the region 400-4000cm -1 on Shimadzu spectrometer using a KBr pellet technique, which was carried out from the Instrumentation laboratory, Jamal Mohamed College, Tiruchirapalli, Tamilnadu. The FT-Raman spectrum of MBSC has been recorded using 1064nm line of Nd: YAG laser as excitation wavelength in the region 50-4000 cm -1 on Bruker RFS27 model spectrometer at the spectral resolution of 2cm -1 carried out from SAIF laboratory, IIT(M), Tamilnadu, India. The ultraviolet absorption spectrum of MBSC is examined in the range of 200-500nm using Perkin Elmer Lambda 35 spectrometer. The UV pattern is taken from a 10 -5 molar solution of MBSC dissolved in methanol and the report was taken from ACIC, St.Joseph's College, Tiruchirapalli, Tamilnadu.

Molecular geomentry
The molecular geometry of (E)-(1)-(4-methonybenzylidene) semicarbazide (MBSC) was studied by the B3LYP/6-311++G (d, p) level of calculation. The geometrical parameters such as bond length, bond angles and dihedral angle are plays a vital role in the formation of molecular structure and its properties. In order to understand the molecular geometry of MBSC, the title molecule was compared with the literature [1]. The bond length of C1-C 2 , C 2 -C 3 , C 3 -C 4 , C 4 -C 5 , C 5 -C 6 , and C 1 -C 6 are calculated as 1. 406 [a]. Similarly the bond length between oxygen and methyl group lies about 1.423A O and the XRD value appeared at 1.437 Å . The bond-length recorded for C=N and C-N were about 1.280 and 1.371 Å, its calculated bond length were lies in the ranges of 1.283 and 1.392A O respectively. The bond N-N being as fuse between C=N and C-N was calculated and recorded about 1.392 and 1.371 Å, which is coincided well with each other. Due to the electron density in C-NH 3 and C=O the bond length of the same decreases when compare with σ bond group. In evident with this the C 21 =O 22 and C 21 -N 23 bond length lies about 1.220 and 1.364 Å which were recorded about 1.241 and 1.336 Å respectively.
The bond angle of methoxy group with the benzene ring (C-O-C) is calculated as 118.87 o and the recorded value of the same was about 117.38 o , it shows a good consent with gas phase molecule.
Similarly the calculated and recorded bond angles of N 19 -C 21 -O 22 and O 22 -C 21 -N 23 are shown very good agreement with each other. The optimized molecular structure of MBSC is shown in fig. 1 and the calculated bond parameters are presented in Table. .

Vibrational analysis
The recorded FT-IR, FT-Raman and calculated wavenumbers along with their relative intensities and probable assignments with TED of the title molecule are given in Table 2. The calculated spectra are found to be close to the experimental values with reasonable accuracy. Comparison of the frequencies calculated at B3LYP with experimental values reveals the overestimation of the calculated vibrational modes due to neglect of anharmonicity in real system. Inclusion of electron correlation in density functional theory (DFT) to a certain extent makes the frequency values smaller in comparison with the 6-311++G (d, p) data.
The in-plane bending vibrations are at higher wave numbers than the out-of-plane vibrations. Shimanouchi [5], assigned the wavenumber data for these vibrations for five different benzene derivatives as a result of normal coordinate analysis. In the present study, the theoretical calculation by B3LYP method predicts the in-plane bending vibration at 983 cm -1 (mode no. 36). The C-C out-of-plane vibration assigned at 635 cm -1 (mode no.47) and 403 cm -1 (mode no.56) in B3LYP method and the corresponding experimental value shows at 628 (w), 405 cm -1 (w) / FT-Raman respectively. The shows the good agreement with literature [5].

C-H Vibrations
Substituted benzenes have large number of sensitive bands, i.e., bands whose position is significantly affected by the mass and electronic properties, mesomeric or inductive of the substituent. According to the literature [6,7], in infrared spectra, most mononuclear and polynuclear aromatic compounds have three or four peaks in the region 2900-3100 cm -1 , these are due to the stretching vibrations of the ring CH bands.
The aromatic C-H stretching vibrations are expected to appear in the range of 3100-3000 cm -1 with some weak bands. The vibrational bands in this region can not affect due to the substituent's [8,9]

C=O, C-O Vibrations
The characteristic infrared absorption frequency of C=O are normally strong in intensity and recorded in the region 1800-1690 cm -1 [11]. The position of C=O stretching is more effective to analyze the various factors in ring aromatic compounds. The C=O bond formed by π-π bond between C and O intermolecular hydrogen bonding, reduces the frequencies of the C=O stretching absorption to a great degree than intermolecular H bonding because of the different electronegatives of C and O the bonding are not equally distributed between the two atoms. The lone pair of electrons on oxygen also determines the nature of the carbonyl groups. In evidence with this, carbonyl peak appeared at 1689 cm -1 as a strong band in FT-IR and DFT result assigned at 1706 cm -1 (mode no.12) with 69% of TED contribution.

C=N, C-N vibrations
The identification of C=N and C-N vibrations are very difficult task since the mixing of several bands are possible in this region [11]. The C=N stretching appears in the region 1600-1670 cm -1 [13], assigned at 1633 cm -1 (FT-IR) and 1625 cm -1 (FT-Raman) to aforementioned band. The C=N (aromatic) stretching mode appeared in the region 1490-1570 cm -1 [14].
In the present study, C=N bond stretching vibration is observed at 1647 cm -1 (as medium strong) in FT-IR spectrum and 1610 cm -1 (as very strong), 1311 (w) in the FT-Raman counterpart. The calculated C=N group frequency lies at 1606 cm -1 (mode no: 13) and 1320 (mode no: 24) using B3LYP/6-311++ G (d, p) basis set, coincide well with the experimental data.
The in-plane bending vibration of δ C=N observed as a mixed vibration of δ H17C16N18 at 1311 cm -1 (w) in FT-Raman whereas the corresponding calculated frequency at 1320 cm -1 (mode no.24) with 25% of TED contribution.
The out-of-plane bending Ґ C=N also contributes a mixed vibration of Ґ N19 N18 C16 H17 (mode no: 39) is recorded as 925 as a calculated frequency with 30% of TED contribution.

C-N vibrations
Silverstein [11], assigned C-N stretching absorption in the region 1382-1266 cm -1 for aromatic amines. For the title compound MBSC, it is interesting to note that both the stretching vibration (ν C-N ) and the in-plane bending vibration (δ C-N ) occur in the same mode (mode no: 19), and the calculated frequency by B3LYP/6-311++G (d,p) is lies at 1438 cm -1 .
The out-of-plane bending lies in the mode numbers: 40, 45 and the respective calculated frequencies lies at 903, 722cm -1 .

NH 2 vibrations
The NH 2 group gives rise to six internal modes of vibrations such as the asymmetric stretching (ν asy ), symmetric stretching (ν sy ), scissoring (δ s ), rocking (δ as) , the symmetric non-planner deformation (wagging) and the anti-symmetric non-planar deformation (torsion). The amino group (NH 2 ) stretching vibration usually appear in the range of 3500-3300cm -1 (Dereli). The NH 2 group in PMSC molecule appears at 3413 cm -1 using FT-IR spectrum, whereas the same group was recorded for MBSC at 3454 cm -1 as a strong band by FT-IR spectrum. The computed frequencies for NH 2 group are about 3592 and 3460 cm -1 (mode no.1and2). The band at 3283 cm -1 was assigned to N-H stretching of hydrozone group, which is negatively deviated for the computed value of 3387 cm -1 at mode number 3.
The scissoring vibration of NH 2 group is appeared at 1510 cm -1 as strong and weak band using FT-IR and FT-Raman spectra respectively. The calculated wavenumber for this mode is about 1530 cm -1 (mode no.16).

Methyl group vibration
The methyl group produces nine vibrations, in which five inplane and four out-of-plane vibrations. When the CH 3 group is directly attached to an oxygen atom, the C-H stretching and bending bands can shift the position due to electronic effects [15]. For aryl methoxy group, the methyl stretching bands occur in the region 3000-2815cm -1 . The methyl group in MBSC molecule shows the symmetric stretching vibration at 2999cm -1 as a medium band in FT-IR and 3003 cm -1 as weak band in FT-Raman spectrum. The asymmetric band for -OCH 3 in MBSC was recorded at 2929 cm -1 (FT-IR/medium). Their corresponding computed values are about 3015 and 2948 cm -1 (mode no: 8 and 9) for symmetric and asymmetric vibration respectively. The TED for methyl group is about 92% symmetric and 100% asymmetric [ν C12H14 (50) , ν C12H15 (50) ].