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Title

Revisited conformational analysis of perhydro-3a,6a,9a-triazaphenalene based on Raman analysis

Authors
Chapuis, Christian
Fieber, Wolfgang
Brauchli, Robert
de Saint Laumer, Jean-Yves
Published in Journal of Physical Organic Chemistry. 2009, vol. 22, no. 4, p. 282-288
Abstract We have demonstrated experimentally by Raman analysis that 1a exists as a mixture of ttt/cct conformers at 22°C in liquid or CCl4 solution, thus contrasting with the initial IR, NMR and X-ray analyses, which were strongly in favour of (ttt)-1a. The global stereoelectronic stabilization is ca. 4.0-4.2 kcal/mol for both parallel N lone pairs (lp) in (cct)-1a, based on a ΔH of 0.75 kcal/mol (±10%), as measured by Raman spectroscopy from 22 to 90°C, as well as the roughly estimated MM2 MeNHEt and MeNHCH2NH2 gauche interactions. DFT calculations using B3LYP/6-31G* yield a standard ΔH value of 1.04 kcal/mol, in good agreement with the experiment, and predict a ttt/cct ratio of ca. 77:23 at 25°C. Broadening of the 13C-NMR signals was observed in either CCl4 or CS2 or even CDCl3 solutions between -20 and -40°C.
Stable URL http://archive-ouverte.unige.ch/unige:15001
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Other version: http://doi.wiley.com/10.1002/poc.1465
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Deposited on : 2011-04-18

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