IR Spectrum and Structure of N-methyl-1,2-benzisothiazol-3-amine 1,1-dioxide: A Combined Matrix Isolation Spectroscopy and Quantum Chemical Calculations Investigation

R. ALMEIDA, A. GÓMEZ-ZAVAGLIA, A. KACZOR, M.L. CRISTIANO, R. FAUSTO.

Luso, Portugal

Congreso; 8º Encontro Nacional da Sociedade Portuguesa de Química.; 2007

Sociedade Portuguesa de Quimica

Saccharin (1,2-benzisothiazol-3(2H)-one-1,1-dioxide) is a commonly known substance as it is the oldest artificial sweetener. Apart from the wide commercial applications of saccharin itself, its derivatives have been attracting an increased attention as they show herbicidal, antimicrobial and antifungal activity or potential in enzymatic inhibition [1]. In this work, the saccharin amino-substituted derivative N-methyl-1,2-benzisothiazol-3-amine 1,1-dioxide (MeBAD) has been studied by matrix isolation FTIR spectroscopy and quantum chemical calculations. Since the computational description of saccharins is difficult because of the presence of the hypervalent S=O bonds in their structures, a series of computational methods (HF, B3LYP, MP2) with basis sets of different sizes have been applied to predict the geometry and vibrational frequencies of the studied compound. According to these calculations, two conformers exist on the potential energy surface of the molecule, differing in the relative orientation of the methyl group in relation to the saccharin moiety: A (N=C-N-C: 0 º) and B (N=C-N-C : 180 º) (see Figure). At the DFT(B3LYP)/6-311++G(d,p) level of theory, conformer B is predicted to be ca. 22 kJ mol-1 less stable than conformer A. Only the latter was experimentally observed, in agreement with the large energy difference between the two conformers predicted theoretically.  Acknowledgement We acknowledge the “Cyfronet” Computer Center, Krakow (Grant KBN/SGI/ORIGIN_2000/UJ/ 044/1999) for computing time and the Portuguese Science Foundation (Grant #SFRH/BPD/ 17081/2004 and projects POCI/QUI/2004: 59019 and 58937). AGZ is member of the Research Career Conicet, Argentina. References [1] P.J. Wepplo, R.A. Rampulla, G.D. Heffernan, M.V. Cosette, C.M. Langevine, V. Kameswaran, R.E. Diehl, M.A. Guaciaro, EP1274708 (2003).