Amino-Imino Tautomerization upon in Vacuo Sublimation of 2-Methyltetrazole-Saccharinate as Probed by Matrix Isolation Infrared Spectroscopy

Ismael, Amin; Gómez-Zavaglia, A.; Borba, A.; Cristiano, Maria Lurdes Santos; Fausto, R.

http://hdl.handle.net/10400.1/4225

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Authors

Ismael, Amin

Gómez-Zavaglia, A.

Borba, A.

Cristiano, Maria Lurdes Santos

Fausto, R.

Abstract(s)

The amino−imino tautomerization of the nitrogen-linked conjugate 2-methyltetrazole-saccharinate (2MTS) was observed upon sublimation of the compound in vacuo. As shown previously by X-ray diffraction [Ismael, A.; Paixão, J. A.; Fausto, R.; Cristiano, M. L. S. J. Mol. Struct., 2011, 1023, 128−142], in the crystalline phase the compound exists in an amino-bridged tautomeric form. Infrared spectroscopic investigation of a cryogenic matrix prepared after sublimation of a crystalline sample of 2MTS and deposition of the sublimate together with argon (in ∼1:1000 molar ratio) onto an IR-transparent cold (15 K) substrate, revealed that the form of 2MTS present in the matrix corresponds to the theoretically predicted most stable imino-bridged tautomer. In this tautomer, the labile hydrogen atom is connected to the saccharine nitrogen, and the two heterocyclic fragments are linked by an imino moiety in which the double-bond is established with the carbon atom belonging to the saccharyl fragment. The observed isomeric form of this tautomer is characterized by a zusammen (Z) arrangement of the two rings around the CN bond of the bridging group and an intramolecular NH···N hydrogen bond. The experimental IR spectrum of the matrix-isolated 2MTS has been fully assigned based on the calculated spectra for the two most stable conformers of this tautomer. A mechanism for the conversion of the tautomeric form existing in the crystal into that present in the gas phase is proposed. As a basis for the interpretation of the experimental results, a detailed theoretical [at the DFT(B3LYP) level of approximation with the 6-31+ +G(d,p) and 6-311++G(3df,3pd)] study of the potential energy surface of the compound was performed.

URI

http://hdl.handle.net/10400.1/4225

Citation

Ismael, Amin; Gómez-Zavaglia, Andrea; Borba, Ana; Cristiano, Maria de Lurdes Santos; Fausto, Rui. Amino-Imino tautomerization upon in vacuo sublimation of 2-methyltetrazole-saccharinate as probed by matrix isolation infrared spectroscopy, The Journal of Physical Chemistry A, 117, 15, 3190 -3197, 2013.