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

We have demonstrated experimentally by Raman analysis that 1a exists as a mixture of ttt/cct conformers at 22 °C in liquid or CCl 4 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 MeNHCH 2 NH 2 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 13 C‐NMR signals was observed in either CCl 4 or CS 2 or even CDCl 3 solutions between −20 and −40 °C. Copyright © 2008 John Wiley & Sons, Ltd.