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Thermally Induced Sigmatropic Isomerization of Pseudosaccharyl Allylic Ether
Gómez-Zavaglia, A.; Kaczor, A.; Almeida, R.; Cristiano, M. L. S.; Eusébio, M. E. S.; Maria, T. M. R.; Mobili, P.; Fausto, R.The thermally induced sigmatropic isomerization of the pseudosaccharyl allylic ether [3-(allyloxy)-1,2-benzisothiazole 1,1-dioxide; ABID] has been investigated by a multidisciplinary approach using temperature dependent infrared spectroscopy, differential scanning calorimetry, and polarized light thermomicroscopy, complemented by theoretical methods. Migration of the allylic system from O to N occurs in the mel...
Matrix-isolation FTIR, theoretical structural analysis and reactivity of amino-...
Almeida, R.; Gómez-Zavaglia, A.; Kaczor, A.; Ismael, A.; Cristiano, M.L.S.; Fausto, R.In this work, two novel amino-substituted derivatives of saccharin, N-(1,1-dioxo-1,2-benzisothiazol-3-yl)-N-methyl amine (MBAD) and N-(1,1-dioxo-1,2-benzisothiazol-3-yl)-N,N-dimethyl amine (DMBAD), were synthesized and characterized, and their molecular structure and vibrational properties were investigated by matrix-isolation FTIR spectroscopy and theoretical calculations undertaken using different levels of a...
First observation of Chapman rearrangement of a pseudosaccharyl ether in the so...
Almeida, R.; Gómez-Zavaglia, A.; Kaczor, A.; Cristiano, M.L.S.; Eusébio, M.E.S.; Maria, T.M.R.; Fausto, R.3-(Methoxy)-1,2-benzisothiazole 1,1-dioxide, a pseudosaccharyl ether, was long ago known to undergo a thermal Chapman-like [1,3′]-isomerization to the corresponding N-methyl pseudosaccharin at temperatures above its melting point (ca. 184 °C) [Hettler H., Tetrahedron Lett.1968, 15, 1793]. In the present study, it is shown that this rearrangement can also take place in the solid state, at temperatures as low as ...
First observation of Chapman rearrangement of a pseudosaccharyl ether in the so...
Almeida, R.; Gómez-Zavaglia, Andrea; Kaczor, A.; Cristiano, M. L. S.; Eusébio, M. E. S.; Maria, T. M. R.; Fausto, R.3-(Methoxy)-1,2-benzisothiazole 1,1-dioxide, a pseudosaccharyl ether, was long ago known to undergo a thermal Chapman-like [1,3']-isomerization to the corresponding N-methyl pseudosaccharin at temperatures above its melting point (ca. 184 °C) [Hettler H., Tetrahedron Lett. 1968, 15, 1793]. In the present study, it is shown that this rearrangement can also take place in the solid state, at temperatures as low as...
The Chapman-type rearrangement in pseudosaccharins: The case of 3-(methoxy)-1,2...
Kaczor, A.; Proniewicz, L.M.; Almeida, R.; Gómez-Zavaglia, A.; Cristiano, M.L.S.; Beja, A.M. Matos; Silva, M. Ramos; Fausto, R.The thermal Chapman-type rearrangement of the pseudosaccharin 3-(methoxy)-1,2-benzisothiazole 1,1-dioxide (MBID) into 2-methyl-1,2-benzisothiazol-3(2H)-one 1,1-dioxide (MBIOD) was investigated on the basis of computational models and knowledge of the structure of the reactant and product in the isolated and solid phases. X-ray diffraction was used to obtain the structure of the substrate in the crystalline phas...
Matrix-Isolated Monomeric Tryptophan: Electrostatic Interactions as Nontrivial...
Kaczor, A.; Reva, I. D.; Proniewicz, L. M.; Fausto, R.An extensive analysis of the conformational space of tryptophan (Trp) was performed at the B3LYP/6-311++G(d,p) level and verified by comparison with the infrared spectra of the compound isolated in low-temperature argon and xenon matrixes. Different types of conformers have been unequivocally identified in the matrixes. Type I exhibits the trans arrangement of the carboxylic group and is stabilized by an O−H···...
Importance of Entropy in the Conformational Equilibrium of Phenylalanine: A Ma...
Kaczor, A.; Reva, I. D.; Proniewicz, L. M.; Fausto, R.The conformational behavior and infrared spectrum of l-phenylalanine were studied by matrix-isolation infrared spectroscopy and DFT [B3LYP/6-311++G(d,p)] calculations. The fourteen most stable structures were predicted to differ in energy by less than 10 kJ mol-1, eight of them with abundances higher than 5% at the temperature of evaporation of the compound (423 K). Experimental results suggest that six conform...
Conformational Behavior of Dimethyl 5-Methyl-1H,3H-pyrrolo[1,2-c][1,3]thiazole-...
Kaczor, A.; Melo, T. M. V. D. Pinho e; Soares, M. I. L.; Fausto, R.The structure of dimethyl 5-methyl-1H,3H-pyrrolo[1,2-c][1,3]thiazole-6,7-dicarboxylate 2,2-dioxide (PTD) was investigated in low-temperature noble gas matrixes (Ar, Kr, Xe), amorphous solid, and the crystalline state by infrared spectroscopy and computational methods. The geometry of PTD conformers is defined by the orientation of two methyl ester groups, which may adopt pseudo-trans or pseudo-cis positions in ...
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