MOLECULAR STRUCTURE AND TAUTOMER EQUILIBRIUM OF GASEOUS 1,2,3-TRIAZOLE STUDIED BY MICROWAVE SPECTROSCOPY, ELECTRON DIFFRACTION AND AB INITIO CALCULATIONS

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1988

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Ohio State University

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Microwave spectra of the parent and the $^{15}N_{3}$ species show the molecule to exist as a mixture of two planar tautomers: a 1**-form with C*** symmetry and a 2**-form with $C_{2v}$ symmetry. The dipole moments of the tautomers have been measured as $\mu_{1H} = 4.38 O$ and $\mu_{2H} = 0.218 O$ in the $^{15}N_{3}$ species. The relative abundance, estimated from rough intensity measurements, is $1H:2H = 1:1000$ at room temperature. Fully optimized geometries have been calculated for the two tautomeric forms of 1,2,3-triazole at the Hartree-Fock SCF level employing a basis set of double zeta quality. The calculations show the 2H-form to be the more stable, with $\Delta E_{1H - 2H} = -14.7 kJ mol^P{-1}$. Structural refinements of a planar $C_{2v}$ model of the 2H-tautomer was carried out based on the electron diffraction data in combination with the measured rotational constants (corrected to $A_{z}, B_{z}$ and $C_{z}$).

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Author Institution: Department of Organic Chemistry, Technical University of Denmark; Department of Chemistry, University of Oslo; Department of Chemistry, Oslo College of Engineering; Department of Chemistry, University of Oslo; Chemical Laboratory v, University of Copenhagen

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