Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Density functional theory study on characterization of 3-chloro-1,2-benzisothiazole
Graphical abstract
The FT-IR and FT-Raman spectra of 3-chloro-1,2-benzisothiazole (CBT) have been recorded and analyzed. The optimized geometry, harmonic vibrational frequencies, infrared and Raman intensities were obtained by means of DFT gradient calculations, using 6-311++G(d,p) basis set. Mulliken population analysis, calculation of thermodynamic properties, HOMO and LUMO energies have been carried out. Stability of the molecule has been analyzed using natural bond orbital analysis (NBO) and natural localized molecular orbital (NLMO) analysis.
Highlights
► The FT-IR and FT-Raman spectra of 3-chloro-1,2-benzisothiazole have been recorded. ► Optimized geometry, vibrational frequencies, IR and Raman intensities are obtained. ► The HOMO and LUMO energies have been calculated. ► Mulliken population analysis shows charge distribution on the molecule. ► Stability of the molecule has been analyzed using NBO and NLMO analysis.
Introduction
Thiazole and their derivatives are some of the most important heterocyclic compounds. The thiazole ring is notable as a component of the Vitamin Thiamine (B1). Many authors have studied these compounds and their properties, such as anti-tubercular [1], [2], [3], [4] and anti-microbial [5], [6], [7], [8] activities. Thiazoles have been known to exhibit biological activities such as bacteriostatic, fungistatic, anti-thrombotic, anti-inflammatory, anesthetic, antihypertensive and sedative. Thiazoles are parent material for numerous of chemical compounds including sulfur drugs, biocides, fungicides and dyes. Thiazole dyes contain the color radicals of CN and SC which decide colors to a compound, and are useful in dying cottons. Mossini et al. [9] have studied the reaction of the title compound 3-chloro-1,2-benzisothiazole (CBT) with diethyl malonate and Carrington et al. [10] have studied the chemical reaction of the title compound with carbanions.
Harmonic force fields of polyatomic molecules play a vital role in the interpretation of vibrational spectra and in the prediction of other vibrational properties. The understanding of their structure, molecular properties as well as the nature of reaction mechanism they undergo have great importance and have been the subject of many experimental and theoretical studies.
The advent of fast computers along with sophisticated computational methods performs the task of solving various structural and chemical problems simple. Ab initio DFT computations have become an efficient tool in the prediction of molecular structure, harmonic force fields, vibrational wavenumbers, IR intensities and Raman activities of biological compounds [11], [12]. These methods predict relatively accurate molecular structure and vibrational spectra with moderate computational effort. Density functional theory (DFT) approaches, using hybrid functional have evolved into a powerful and very reliable tool, being routinely used for the determination of various molecular properties. B3LYP functional had been previously shown to provide an excellent compromise between accuracy and computational efficiency of vibrational spectra for large and medium size molecules [13], [14], [15], [16]. It is well known that vibrational frequencies obtained by quantum chemical calculations are typically larger than their experimental counterparts, and thus, empirical scaling factors are generally used to obtain better experimental frequencies [17]. These scaling factors depend both on the method and basis sets used in calculations and they are determined from the mean deviation between the calculated and experimental frequencies [18], [19].
Literature survey reveals that to the best of our knowledge, no ab initio DFT frequency calculations of the title compound CBT have been reported so far. Therefore, the present investigation has been undertaken to study the molecular structure, geometrical parameters, vibrational wavenumbers, modes of vibrations and various thermodynamic properties, and the Natural Bond Orbital (NBO)/Natural Localized Molecular Orbital (NLMO) analysis which explains the most important orbital interactions in order to classify general structural features. The Mulliken population analysis and the HOMO–LUMO energies have also been calculated.
Section snippets
Experimental details
The fine polycrystalline sample of 3-chloro-1,2-benzisothiazole was purchased from Alfa Aesar Chemical company, UK with a stated purity of 98% and it was used as such without further purification. The room temperature Fourier transform infrared spectra of the title compound was measured in the region 4000–400 cm−1 at a resolution of ±1 cm−1 using a JASCO FT/IR-6300 spectrometer. KBr pellets were used in the spectral measurements. Boxcar apodization was used for 250 averaged interferograms
Computational details
The molecular geometry optimizations, calculations of energy, vibrational frequencies, IR intensities and Raman activities were carried out for 3-chlroro-1,2-benzisothiazole (CBT) with the GAUSSIAN 09 software package [20] using DFT/B3LYP functional [21], [22] combined with the standard 6-311++G(d,p) basis set. Initial geometry generated from the standard geometrical parameters was minimized without any constraint on the potential energy surface at Hartree-Fock level adopting the standard
Molecular geometry and structural properties
The first task for the computational work is to determine the optimized geometry of the studied molecule. The molecular structure and numbering of the atoms of CBT are shown in Fig. 1. The global minimum energy obtained by DFT/B3LYP with 6-311++G(d,p) basis set for CBT is calculated as −1182.41957051 Hartrees. The optimized geometrical parameters of CBT obtained by DFT/B3LYP with 6-311++G(d,p) basis set are presented in Table 1 by comparing with the experimental XRD bond lengths and angles [31].
HOMO–LUMO analysis
In principle, there are several ways to calculate the excitation energies. The simplest one involves the difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of a neutral system, which is a key parameter in determining molecular properties [47]. Moreover, the Eigen values of HOMO (π donor) and LUMO (π acceptor) and their energy gap reflect the chemical activity of the molecules. Recently, the energy gap between HOMO and LUMO has
NBO/NLMO analysis
NBO (Natural Bond Orbital) analysis provides an efficient method for studying intra and inter molecular bonding and interaction among bonds, and also provides a convenient basis for investigation charge transfer or conjugative interactions in molecular system [50]. Another useful aspect of NBO method is that it gives information about interactions in both filled and virtual orbital spaces that could enhance the analysis of intra and intermolecular interactions. The second order Fock matrix was
Conclusion
The structural characteristics and fundamental modes of the compound 3-chloro-1,2-benzisothiazole have been investigated by FTIR and FT-Raman spectroscopic techniques. The molecular structural parameters, thermodynamic properties, vibrational frequencies and electronic excitations of the optimized geometry of 3-chloro-1,2-benzisothiazole have been obtained from DFT-B3LYP method using 6-311++G(d,p) basis set. The vibrational frequencies of the fundamental modes of the compound have been
Acknowledgements
The authors are thankful to Sree Chitra Tirunal Institute for Medical Sciences and Technology Thiruvananthapuram, India for providing spectral facilities. The authors are also thankful to Manonmaniam Sundaranar University, Tirunelveli, India.
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