FTIR, FT-Raman and DFT Calculations of 5-nitro-1,3-Benzodioxole

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1 Est. 984 ORIENTAL JOURNAL OF CHEMISTRY An International Open Free Access, Peer Reviewed Research Journal ISSN: X CODEN: OJCHEG 202, Vol. 28, No. (2): Pg FTIR, FT-Raman and DFT Calculations of 5-nitro-,3-Benzodioxole C.YOHANNAN PANICKER *, HEMA TRESA VARGHESE 2 and Y. SHEENA MARY 2 Department of Physics, TKM College of Arts and Science, Kollam, Kerala (India). 2 Department of Physics, Fatima Mata National College, Kollam, Kerala (India). *Corresponding author cyphyp@rediffmail.com (Received: February 20, 202; Accepted: March 30, 202) ABSTRACT FTIR and FT-Raman spectrum of 5,-benzo-,3-benzodioxole were recorded and analyzed. The vibrational wavenumbers were examined theoretically using the Gaussian03 set of quantum chemistry codes. The experimental frequencies are in agreement with the calculated (B3LYP) scaled values. The predicted infrared intensities and Raman activities are reported. Key words: FTIR, FT-Raman, DFT, benzodioxole. INTRODUCTION Thebenzodioxole ((methylenedioxy) benzene) group is present in a number of endothelin receptor antagonists. Endothelins are 2-amino acid bicyclic peptides originally isolated from the supernatant of cultured porcine endothelial cells. There have been many studies about the molecular conformations of indan-like benzene fused ring molecules 2-4. These molecules have received considerable attention due to their interesting conformational properties. Laane et al. reported the infrared, Raman, electronic UV absorption, and laser induced fluorescence excitation spectra of two oxygen containing indan-like molecule, phthalan 5-7 and,3-benzodioxole 8,9.,3-benzodioxole has been studied extensively by several spectrographic and theoretical methods owing to its propensity for large amplitude motion 0-2. It is believed that the molecule has a nonplanar structure in its electronic ground state. While the aromatic ring is planar, the five member ring is puckered, with the oxygen atoms and the group on opposite side of the aromatic plane. In the present work, the vibrational spectroscopic analysis of 5-nitro-,3-benzodioxole is reported, experimentally and theoretically. EXPERIMENTAL The FT-IR spectrum was recorded on a DR/Jasco FT-IR 6300 spectrometer in KBr pellets, number of scans 6, resolution 2 cm -. The FT- Raman spectrum was obtained on a BRUKER RFS 00/S, Germany. For excitation of the spectrum the

2 038 PANICKER et al., Orient. J. Chem., Vol. 28(2), (202) emission of a Nd:YAG laser was used, excitation wavelength 064 nm, maximal power 50 mw. One thousand scans were accumulated with a total registration time of about 30 min. The spectral resolution after apodization was 2 cm -. COMPUTATIONAL DETAILS Calculations of the title compound were carried out with Gaussian03 software program 3 using the B3LYP/6-3G* basis sets to predict the molecular structure and vibrational wavenumbers. The DFT hybrid B3LYP functional tends also to overestimate the fundamental modes; therefore scaling factors have to be used for obtaining a considerably better agreement with experimental data. Therefore, a scaling factor of was uniformly applied to the DFT calculated wavenumbers 4. The assignment of the calculated wavenumbers is aided by the animation option of MOLEKEL program, which gives a visual presentation of the vibrational modes 5,6. RESULTS AND DISCUSSION The observed IR, Raman and calculated (scaled) wavenumbers and the assignments are given in Table. In nitro compounds, υ as are located in the region 580 ± 80 cm -. The nitro benzene derivatives 7 shows υ as in the region 535 ± 30cm - and the 3-nitropyridine at 530 ± 20cm -. In the present case, υ as are obtained at 596 theoretically and at 609 cm - in IR spectrum. In nitro compounds, υ s are located in the region 400 ± 40 cm -. For the title compound, υ s is observed at 427 cm - (DFT), 437 cm - (IR) and 430 cm - (Raman). In the aromatic nitro compounds, bands are usually seen at 855 ± 40cm - ( scissors deformation δ ), 760 ± 30cm - ( out of plane wag ω ), 580 ± 30cm - ( inplane rock σ ) and 70 ± 20cm - (τ ). In the present case, the observed values for δ are 97 (DFT), 920 (IR) cm - ; ω is 803 cm - (DFT), ; σ are 666 (DFT) and τ is at 2cm - (DFT). Panicker et al. 8 reported the deformation bands at 800, 724, 534 cm - (theoretically) and 809, 727, 77, 524 cm - (experimentally). Sundaraganesan et al. 9 reported the deformation bands at 839, 744 and 398cm - experimentally and 82, 76,703 and 327 cm - theoretically. For methylene groups 20, the vibrations are observed in the region , , and cm -. The vibrations of the group (the asymmetric stretch υ as, symmetric stretch υ s, the scissoring vibration and wagging vibration) appear in the regions , , and cm -, respectively 7, 2. The stretching bands of the groups are observed at 2925 cm - in the IR spectrum and at 2992, 2942 cm - theoretically for the title compound. According to literature scissoring mode of the group give rise to characteristic band near 485 cm - in IR and Raman spectra. This mode is observed at 489 cm - in the IR spectrum and at 474 cm - theoretically. The wagging mode

3 PANICKER et al., Orient. J. Chem., Vol. 28(2), (202) 039 Table :Calculated (scaled) wavenumbers, IR, Raman bands and assignments B3LYP/6- IR Raman IR Raman Assignments 3G* intensity activity υ(cm - ) υ(cm - ) υ(cm - ) υch υch υch υ as υ s υph υ as υph υph δ υ s υph ω υph υcn υcoc υcoc δch δch τ υcoc υcoc,δch γch δ σ γch γch ω υph γch γph δph(x) σ γph(x) δph(x) γph(x) δph(x) δcx(x) δcx(x) γcx(x) γcx(x) δcx(x) γcx(x) tph t υ-stretching; δ-in-plane deformation; γ-out-of-plane deformation; ω-wagging; σ-rocking; t-torsion; as-asymmetric; s-symmetric; Ph-phenyl ring; X-substituent sensitive.

4 040 PANICKER et al., Orient. J. Chem., Vol. 28(2), (202) is observed at 378 cm - in the Raman spectrum and at 372 cm - theoretically. The twisting and rocking vibrations of the group appear in the region 7 of and cm -, respectively. These modes are also assigned. For the title compound the twisting vibration is observed at 5 cm - in the IR spectrum and at 00 cm - theoretically. The rocking deformation is assigned at 907 cm - theoretically. The asymmetric and symmetric C-O-C stretching vibrations are expected to appear at and cm In the present case the DFT calculations give these modes at 224, 60, 046 and 027 cm -. The bands at 7, 066, 036 (IR) and 05, 028 cm - (Raman) are assigned as C-O-C symmetric stretching modes. The C-O-C stretching modes are reported at 250, 073 cm - for 2-mercaptobenzoxazole 23, 263, 055 cm - for 5-methyl-2-(p-fluorophenyl)benzoxazole 24. The existence of one or more aromatic rings in a structure is normally readily determined from the C H and C=C C related vibrations. The C H stretching occurs above 3000 cm - and is typically exhibited as a multiplicity of weak to moderate bands, compared with the aliphatic C H stretch 25. In the present case, the DFT calculations give the υch modes at 345, 334 and 30 cm -. The band observed at 39 cm - in the IR spectrum is assigned as υch mode of the benzene ring. The benzene ring possesses six ring stretching vibrations, of which the four with the highest wavenumbers (occurring near 600, 580, 490 and 440 cm - ) are good group vibrations 7. In the absence of ring conjugation, the band near 580 cm - is usually weaker than that at 600 cm -. The fifth ring stretching vibration which is active near 335 ± 35 cm - a region which overlaps strongly with that of the CH in-plane deformation and the intensity is in general, low or medium high 7. The sixth ring stretching vibration or ring breathing mode appears as a weak band near 000 cm - in mono,,3-di and,3,5-trisubstituted benzenes. In the other wise substituted benzene, however, this vibration is substituent sensitive and difficult to distinguish from the ring in-plane deformation. For tri-substituted phenyl ring the υph modes 7 are seen in the region cm - and these modes are observed at 632, 55, 56, 38, 345 cm - in the IR spectrum, 620, 333 cm - in the Raman spectrum and at 69, 563, 55, 395, 336 cm - (DFT) theoretically. In asymmetric tri-substituted benzenes, when all the three substituents are light, the wavenumber interval of the breathing mode 26 is between 500 and 600 cm -. When all the three substituents are heavy, the wavenumber appears above 00 cm -. In the case of mixed substituents, the wavenumber is expected 26 to appear between 600 and 750 cm -. For the title compound the phenyl ring breathing mode is assigned at 796 cm - theoretically. Mary et al. 27 reported the ring breathing mode of tri-substituted benzene ring at 733 cm - in the IR spectrum and at 738 cm - theoretically. The in-plane bending δch modes 7 of the phenyl ring are expected above 000 cm -. For the tri-substituted benzene ring these modes are observed at 20, 036 cm - in IR, 28, 028 cm - in Raman and at 44, 03, 027 cm - theoretically. The CH out-of-plane deformations 7 are observed between 000 and 700 cm -. Generally the CH out-of-plane deformations with the highest wavenumbers have a weaker intensity than those absorbing at lower wavenumbers. These γch modes are observed at 872, 80, 79 (IR), 809, 725 (Raman), 864, 806, 72 cm - (DFT). The in-plane and out-of-plane substituent modes of the phenyl ring are also identified and assigned (Table ). CONCLUSION The FTIR and FT-Raman spectra of 5- nitro-,3-benzodioxole were recorded and analyzed. The harmonic vibrational wavaenumbers were calculated theoretically using Gaussian03 set of quantum chemistry codes. The calculated wavenumbers (B3LYP) agree well with the observed wavenumbers. The small differences between experimental and calculated vibrational modes are observed. It must be due to the fact that hydrogen bond vibrations present in the crystal lead to strong perturbation of the infrared wavenumbers and intensities of many other modes. Also we state that the experimental results belong to solid phase and theoretical calculations belong to gaseous phase.

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