The Fourier Transform (FT) infrared and FT-Raman spectra of benzothiazole (BT) have been recorded and analyzed. The equilibrium geometry, bonding features, and harmonic vibrational frequencies have been investigated by ab initio and density functional theory (DFT) methods. The assignments of the vibrational spectra have been carried out. The computed optimized geometric bond lengths and bond angles show good agreement with experimental data of the title compound. The calculated HOMO and LUMO energies indicate that charge transfer occurs within the molecule. Stability of the molecule due to conjugative interactions arising from charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that the electron density (ED) in the and antibonding orbital and second-order delocalization energies confirm the occurrence of intramolecular charge transfer (ICT). The calculated results were applied to simulate infrared and Raman spectra BT which show good agreement with recorded spectra. 1. Introduction Benzothiazole (BT) molecule contains a thiazole ring fused with benzene ring. Thiazole ring is a five-member ring consists of one nitrogen and one sulfur atom in the ring. Benzothiazole is thus a bicyclic aromatic ring system. A number of BT derivatives have been studied as central muscle relaxants and found to interfere with glutamate neurotransmission in biochemical, electrophysiological, and behavioral experiments [1]. Substituted benzothiazoles have been studied and found to have various chemical reactivity and biological activity. Benzothiazole ring is found to possess pharmacological activities such as antiviral [2], antibacterial [3], anti-microbial [4], and fungicidal activities [5]. They are also useful as antiallergic [6], antidiabeticantitumor [7], antitumor [8], anti-inflammatory [9], anthelmintic [10], and anti-HIV agents. Phenyl substituted benzothiazoles show antitumor activity [11–13] while condensed pyrimido benzothiazoles and benzothiazoloquinazolines show antiviral activity. Substituted 6-nitro- and 6-amino-benzothiazoles show antimicrobial activity. Molecular spectroscopic methods, in particular, experimental IR and Raman spectroscopy, have been successfully employed for structural investigation of complex molecular compounds. These techniques are especially effective when used in combination with direct methods of structural analysis in hydrogen bond investigations. The aim of the present work is theoretical and experimental spectroscopic investigation of BT molecular structure to gain insight into the
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