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

Published inJournal of physical organic chemistry, vol. 22, no. 4, p. 282-288
Publication date2009
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.

Citation (ISO format)
CHAPUIS, Christian et al. Revisited conformational analysis of perhydro-3a,6a,9a-triazaphenalene based on Raman analysis. In: Journal of physical organic chemistry, 2009, vol. 22, n° 4, p. 282–288. doi: 10.1002/poc.1465
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ISSN of the journal0894-3230
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